Catalytic Olefin Polymerization: Proceedings of the International Symposium on Recent Developments in Olefin Polymerization Catalysts, Tokyo, Octobe

Studies in Surface Science and Catalysis 56

CATALYTIC OLEFIN POLYMERIZATION

Proceedings of the International Symposium on Recent Developments in Olefin Polymerization Catalysts, Tokyo, October 23- 25, 1989

This Page Intentionally Left Blank

Studies in Surface Science and Catalysis Advisory Editors : B. Delmon and J. T. Yates

Vol. 56

CATALYTIC OLEFIN PO LY M ERIZATION PROCEEDINGS OF THE INTERNATIONAL SYMPOSIUM ON RECENT DEVELOPMENTS IN OLEFIN POLYMERIZATION CATALYSTS, TOKYO, OCTOBER 23-25,1989

Edited by

Tominaga Keii

Kazuo Soga

Professor Emeritus, Tokyo Institute of Technology

Professor, Tokyo Institute of Technology

ELSEVIER 1990

KODANSHA

Tokyo Amsterdam-Oxford- New York-Tokyo

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List of Contributors Numbers in parentheses indicate the chapter (5 ) in which the authors’ contributions appear.

Albornoz, A. (29) Polymer Laboratory, Chemistry Center, IVIC, Apartado 21827, Caracas 1020A, Venezuela Almquist, V. (6) Statoil, 3960 Stathelle, Norway Antberg, M. (35) Hoechst AG, 6230 Frankfurt a. Main 80, F.R.G. Arzoumanidis, G.G. (12) Amoco Chemical Company, P. 0. Box 3011, Naperville, Illinois 60566, U.S.A. Barazzoni, L. (28) EniChem Anic S.p.a., Polyolefins Division, Catalysts Research, S.Donato Milanese, Milano, Italy Bark, A. (31) Institut fiir Anorganische und Angewandte Chemie, Universitat Hamburg, Martin-Luther-King Platz 6, 2 Hamburg 13, F.R.G. Bernard, A. (30) Solvay et Cie S.A., Laboratoire Central, Rue de Ransbeek 310, B-1120 Bruxelles, Belgique Bobichon, C. (3) (8) CNRS, Laboratoire des Materiaux Organiques, BP 24, 69390 Vernaison, France

B-, C. (9) Groupe de Recherches de Lacq, BP34 LACQ, 64170 Artix, France Bu, N. (4) Department of Chemical Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G6

Chang, H.S. (21) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, P.O. Box 131 Cheongryang, Seoul, Korea Cheng, H.N. (32) Research Center, Hercules Incorporated, Wilmington, Delaware 19894, U.S.A. Chida, K. (15) Tonen Sekiyukagaku K.K., Tonen Corporate Research & Development Laboratory, Inuna-gun, Saitama 354, Japan

vj List of Contributors

Chien, J.C.W. (38) Department of Polymer Science and Engineering, Department of Chemistry, University of Massachusetts, Amherst, MA 01003, U.S.A. Choi, H.K: (26) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul, Korea Chu, K.J. (21) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, P. 0. Box 131, Cheongryang, Seoul, Korea Chung, M.C. (26) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, P.O.Box 131, Cheongryang, Seoul, Korea Curtis, S. (32) Fina Oil and Chemical Company, P.O. Box 1200, Deer Park, Texas 77536, U.S.A. Dake, I. (31) Institut fur Anorganische und Angewandte Chemie, Universitat Hamburg, Martin-Luther-King Platz 6, 2 Hamburg 13, F. R. G Dolle, V. (35) Hoechst AG, 6230 Frankfurt a. Main 80, F. R. G. Duranel, L. (8) Atochem G.R.L., BP 34 LACQ, 64170 Artix, France Elder, M.J. (32) Fina Oil and Chemical Company, P.O. Box 1200, Deer Park, Texas 77536, U.S.A. Endo, K. (18) Department of Applied Chemistry, Faculty of Engineering, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka 558, Japan Ewen, J.A. (32) Fina Oil and Chemical Company, P.O. Box 1200, Deer Park, Texas 77536, U.S.A. Fenzl, W. (19) Max-Planck-Institut & Kohlenforschung, Kaiser-Wilhelm-Platz-1, D-4330 Mulheim a.d. Ruhr-1, F. R. G. Ferrero, C. (28) EniChem Anic S.p.a., Polyolefins Division, Catalysts Research, S.Donato Milanese, Milano, Italy Fiasse, P. (30) Solvay et Cie S.A., Laboratoire Central, Rue de Ransbeek 310, B-1120 Bruxelles, Belgique Fink, G.(19) Max-Planck-Institut fur Kohlenforschung, Kaiser-Wilhelm-Platz-1, D-4330 Miilheim a.d.

Follestad, A. (6) Statoil, 3960, Stathelle, Norway

Ruhr-1, F.R.G.

Listof Gmhibum vii

Fuentes, A. (29) Polymer Laboratory, Chemistry Center, IVIC, Apartado 21827, Caracas 1020A, Venezuela Fujita, T. (17) Yokkaichi Research Center, Mitsubishi Petrochemical Co., Ltd., 1 Toho-cho, Yokkaichi, Mie 510, Japan Furuhashi, H. (14) (15) Tonen Sekiyukagaku K.K., Tonen Corporate Research & Development Laboratory, Inuna-gun, Saitama 354, Japan Grubbs, R.H. (24) Arnold and Mabel Bechman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena CA 91125, U S A . Guyot, A. (3) (8) CNRS, Laboratoire des Materiaux Organiques, BP 24, 69390 Vernaison, France Harkonen, M. (7) Helsinki University of Technology, Department of Chemical Engineering, Kemistintie 1, SF-02150 Espoo, Finland Hattori, I. (25) Elastomers Laboratory, Technical Center, Japan Synthetic Rubber Co., Ltd., 100 Kawajiri-cho, Yokkaichi, Mie 510, Japan Helleborg, S. (6) Statoil, 3960 Stathelle, Norway Herfert, N. (19) Max-Planck-Institut fur Kohlenforschung, Kaiser-Wilhelm-Platz-1, D-4330 Miilheim a.d. Ruhr-1, F.R.G. Ihm, S.K. (21) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, P. 0. Box 131, Cheongryang, Seoul, Korea Iiskola, E. (11) Polyolefins R & D, Neste Chemicals, SF-06850 Kulloo, Finland Imai, M. (14) Tonen Sekiyukagaku K.K., Tonen Corporate Research & Development Laboratory, Iruma-gun, Saitama 354, Japan Invernizzi, R. (28) EniChem Anic S.p.a., Polyolefins Division, Catalysts Research, S.Donato Milanese, Milano, Italy Ishii, K. (22) Toho Titanium Co. Ltd., 3-3-5 Chigasaki, Chigasaki-shi, Kanagawa 253, Japan Jaber, I.A. (2) (19) Max-Planck-Institut fur Kohlenforschung, Kaiser-Wilhelm-Platz-1, D-4330 Mdheim a.d. Ruhr-1, F. R. G. (present address) Jejelowo, M.O. (4) Department of Chemical Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G6

vii List of Contributors

Job, J.F. (9) CNRS, Laboratoire des Materiaux Organiques, BP 34, 69390 Vernaison, France Jones, R.L. (32) Fina Oil and Chemical Company, P.D. Box 1200, Deer Park, Texas 77536, U.S.A. Kakugo, M. (13) (27) (36) Chiba Research Laboratory, Sumitomo Chemical Co. Ltd., 2-1 Kitasode, Sodegaura-cho, Kimi- tsu-gun, Chiba 299-02 Japan Kaminsky, W. (31) Institut fur Anorganische und Angewandte Chemie, Universitat Hamburg, Martin-Luther-King Platz 6, 2 Hamburg 13, F.R.G. Kang, K.S. (21) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul, Korea Karayannis, N.M. (12) Amoco Chemical Company, P.O.Box 3011, Naperville, Illinois 60566, U.S.A. Kashiwa, N. (33) (34) Iwakuni Polymer Research Laboratories, Mitsui Petrochemical Industries, Ltd., Waki -cho, Kuga-gun, Yamaguchi 740, Japan Kataoka, T. (5) Toho Titanium Co. Ltd., 3-3-5253, Chigasaki, Chigasaki-shi, Kanagawa 253, Japan Keii, T. (1) (5) Tokyo Institute of Technology, Preparation Committee of JAIST, Monbusho 7F1, Kasumigaseki 3-2-2, Chiyoda-ku, Tokyo 100, Japan Kim, I. (26) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, P.O.Box 131, Cheongryang, Seoul, Korea Kim, J.H. (26) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, P.O.Box 131, Cheongryang, Seoul, Korea Kioka, M. (33) (34) Iwakuni Polymer Research Laboratories, Mitsui Petrochemical Industries, Ltd., Waki-cho, Kuga-gun, Yamaguchi 740, Japan Klein, R. (35) Hoechst AG,6230 Frankfurt a. Main 80, F.R.G. Lacombe, J.L. (3) DPPG, Atochem, Mont, BP 3 Argagnon, 64300 Orthez, France Lin, s. (20) Institute of Polymer Science, Zhongshan University, Guangzhou, China Liscano, J. (29) Polymer Laboratory, Chemistry Center, IVIC, Apartado 21827, Caracas 1020A, Venezuela

List of Gmtribntm ix

Loontjens, A.J. (2) DSM, Research and Patents, Geleen, Holland Lynch, D.T. (4) Department of Chemical Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G6 Makino, K. (25) Elastomers Laboratory, Technical Center, Japan Synthetic Rubber Co., Ltd., 100 Kawajiri-cho, Yokkaichi, Mie 510, Japan Mallin, D.T. (38) Department of Polymer Science and Engineering, Department of Chemistry, University of Massachusetts, Amherst, MA 01003, U.S.A. Malquori, S. (28) EniChem Anic S.p.a., Polyolefins Division, Catalysts Research, S.Donato Milanese, Milano, Italy Masi, F. (28) EniChem Anic S.p.a., Polyolefins Division, Catalysts Research, S.Donato Milanese, Milano, Italy Menconi, F. (28) EniChem Anic S.p.a., Polyolefins Division, Catalysts Research, S.Donato Milanese, Milano, Italy Mise, T. (37) The Institute of Physical and Chemical Research, Hirosawa, Wako-shi, Saitama 351-01, Japan Miya, S. (37) Chisso Petrochemical Corporation, 5- 1 Goikaigan, Ichihara-shi, Chiba 290, Japan Miyatake, T. (13) (36) Chiba Research Laboratory, Sumitomo Chemical Co. Ltd., 2-1 Kitasode, Sodegaura-cho, Kmi- tsu-gun, Chiba 299-02, Japan Mizunuma, K. (13) (36) Chiba Research Laboratory, Sumitomo Chemical Co. Ltd., 2-1 Kitasode, Sodegaura-cho, Kimi- tsu-gun, Chiba 299-02, Japan Moalli, A. (28) EniChem Anic S.p.a., Polyolefins Division, Catalysts Research, S.Donato Milanese, Milano, Italy Miiller, T. (19) Max-Planck-Institut fur Kohlenforschung, Kaiser-Wilhelm-Platz-1, D-4330 Mulheim a.d. Ruhr-1, F.R.G. Munoz-Escalona, A. (29) Polymer Laboratory, Chemistry Center, IVIC, Apartado 21827, Caracas 1020A, Venezuela Murata, M. (14) Tonen Sekiyukagaku K.K., Tonen Corporate Research & Development Laboratory, Iruma-gun, Saitama 354, Japan Nakano, A. (14) (15) Tonen Sekiyukagaku K.K., Tonen Corporate Research & Development Laboratory, Iruma-gun, Saitama 354, Japan

x List of Contributors

Noristi, L. (16) Himont Centro Ricerche Giulio Natta, Piazzale Donegani 12, 44100 Ferrara, Italy Okano, T. (15) Tonen Sekiyukagaku K.K., Tonen Corporate Research & Development Laboratory, Iruma-gun, Saitama 354, Japan Otsu, T. (18) Department of Applied Chemistry, Faculty of Engineering, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka 558, Japan Pakkanen, T.A. (11) Department of Chemistry, University of Joensuu, SF-80101 Joensuu, Finland Pakkanen, T.T. (11) Department of Chemistry, University of Joensuu, SF- 80101 Joensuu, Finland Park, J.R. (10) Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 227, Japan Rausch, M.D. (38) Department of Polymer Science and Engineering, Department of Chemistry, University of Massachusetts, Amherst, MA 01003, U.S.A. Rieger, B. (38) ZKP/Polyolefin, BASF AG 6700, Ludwigshafen, F.R.G. (present address) Rohrmann, J. (35) Hoechst AG, 6230 Frankfurt a. Main 80, F.R.G. Sacchi, M.C. (16) Istituto di Chimica delle Macromolecole del CNR, Via E. Bassini 15/A-20133 Milano, Italy Sadatoshi, H. (27) Chiba Research Laboratory, Sumitomo Chemical Co. Ltd., 5-1 Anesakikaigan, Ichihara-shi, Chiba 299-01, Japan Sakai, J. (27) Chiba Research Laboratory, Sumitomo Chemical Co. Ltd., 5- 1 Anesakikaigan, Ichihara-shi, Chiba 299-01, Japan Sakakibara, M. (25) Elastomers Laboratory, Technical Center, Japan Synthetic Rubber Co., Ltd., 100 Kawajiri-cho, Yokkaichi, Mie 510, Japan Seppala, J.V. (7) Helsinki University of Technology, Department of Chemical Engineering, Kemistintie 1, SF-02150 ESPOO, Finland Shan, C. (16) Istituto di Chimica delle Macromolecole del CNR, Via E. Bassini 15/A-20133 Milano, Italy Shiono, T. (23) Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 227, Japan

Soga, K. (10) (23) Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 227, Japan Sormunen, P. (11) Polyolefins R & D, Neste Chemicals, SF-06850 Kulloo, Finland Spaleck, W. (35) Hoechst AG, 6230 Frankfurt a. Main 80, F.R.G.

Spitz, R. (3) (8) (9) CNRS, Laboratoire des Materiaux Organiques, BP 24, 69390 Vernaison, France Sugano, T. (17) Yokkaichi Research Center, Mitsubishi Petrochemical Co. Ltd., 1 Toho-cho, Yokkaichi, Mie 510, Japan Sugimoto, R. (38) Osaka Reseach Laboratory, Mitsui Toatsu Chemicals Inc., 6- 1-chome Takasago, Takaishi, Osaka 592, Japan (present address) Sun, L. (20) Institute of Polymer Science, Zhongshan University, Guangzhou, China Tait, P.J.T. (2) Chemistry Department, University of Manchester, Institute of Science and Technology, P.O. Box 88, Manchester, M60 lQD, England Terano, M. (5) (22) Toho Titanium Co. Ltd., 3-3-5 Chigasaki, Chigasaki-shi, Kanagawa 253, Japan Toyota, A. (34) Iwakuni Polymer Research Laboratories, Mitsui Petrochemical Industries, Ltd., Waki-cho, Kuga-gun, Yamaguchi 740, Japan Tritto, I. (16) (24) Istituto di Chimica delle Mecromolecole del CNR, Via E. Bassini 15/A-20133 Milano, Italy

Tsutsui, T. (33) (34) Iwakuni Polyqer Research Laboratories, Mitsui Petrochemical Industries, Ltd., Waki-cho, Kuga-gun, Yamaguchi 740, Japan Tsutsumi, F. (25) Elastomers Laboratory, Technical Center, Japan Synthetic Rubber Co. Ltd., 100 Kawajiri-cho, Yokkaichi, Mie 510, Japan Ueda, T. (33) Iwakuni Polymer Research Laboratories, Mitsui Petrochemical Industries, Ltd., Waki-cho, Kuga-gun, Yamaguchi 740, Japan Ueki, S. (15) Tonen Sekiyukagaku K.K., Tonen Corporate Research & Development Laboratory, Iruma-gun, Saitama 354, Japan Vaananen, T. (7) Neste Chemicals, P.O.Box 310, SF-06101 Porvoo, Finland

x i List of Contributors

Viihasarja, E. (11) Department of Chemistry, University of Joensuu, SF-80101, Joensuu, Finland Wanke, S.E. (4) Department of Chemical Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G6 Winter, A. (35) Hoechst AG, 6230 Frankfurt a. Main 80, F. R. G. Woo, S.I. (26) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, P.O.Box 131, Cheongryang, Seoul, Korea

Wu, Q. (20) Institute of Polymer Science, Zhongshan University, Guangzhou, China Yamamoto, Y. (17) Yokkaichi Research Center, Mitsubishi Petrochemical Co. Ltd., 1 Toho-cho, Yokkaichi, Mie 5 10, Japan

Yamazaki, H. (37) The Institute of Physical and Chemical Research, Hirosawa, Wako-shi, Saitama 351 -01, Japan Yoshida, K. (23) Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 227, Japan

Contents

..................................................................................................................... List of Contributors V Preface xvii .................................................................................................................................

1.

2.

3.

4.

5.

6.

7.

a.

9.

A Theory of Time-Invariant Molecular Weight Distributions in Heterogeneous Ziegler -Natta Polymerizations (T. Keii)

Studies on the Polymerization of Propylene Using Highly Active Magnesium Chloride Supported Ziegler -Natta Catalysts : Effects of Alkyl Concentration on the Polymerization Rate and on the Active Centre Concentration (P. J. T. Tait, I. A.Jaber and A. J. Loontjens)

Gas Phase Polymerization of Propene with MgCl2 Supported Catalyst (A. Guyot, R. Spitz, C. Bobichon and J. L. Lacombe)

Ethylene Polymerization in Gas-Phase and Slurry Reactors (M. 0. Je- jelowo, N. Bu, D. T. Lynch and S. E. Wanke)

Differences in Kinetic Parameters of Various Kinds of MgC12-Sup- ported High Yield Catalysts (M. Terano, T. Kataoka and T. Keii)

Kinetic Profile of Polymerization with Cr-Oxide/SiOz Catalyst (A. Follestad, S. Helleborg and V. Almquist)

Effects of the Structure of External Alkoxy Silane Donor in High Ac- tivity Ziegler -Natta Catalyst on the Microstructure of Polypropylene (M. Harkonen, J. V. Seppala and T. Vainanen)

Active Center Selection and Propene Polymerization Control with the New Supported Ziegler-Natta Catalysts (R. Spitz, C. Bobichon, L. Duranel and A. Guyot)

Control of the Catalyst and Polymer Properties of Linear Polyethylenes (R. Spitz, C. Brun and J. F. Joly)

1

11

29

39

55

63

87

107

117

xiv Contents

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

Easy Conversion of Aspecific into Isospecific Sites (K. Soga and J. R. Park)

A 13C CP-MAS NMR and Elemental Analysis Study of Adsorption of Silyl Ethers on the MgClz-Supported Ziegler-Natta Catalysts (P. Sor-munen, T. T. Pakkanen, E. Vahisarja, T. A. Pakkanen and E. Iiskola)

Infrared Characterization of Supported Propylene Polymerization Catalysts- A Link to Catalyst Performance (G. G. Arzoumanidis and N. M. Karayannis)

Microtacticity Distribution of Polypropylenes Prepared with MgC12 Supported Ti Catalyst Systems (T. Miyatake, K. Mizunuma and M. Kakugo)

Development of SiOz-Supported Type Catalyst for Propylene Molymerization (M. Murata, A. Nakano, H. Furuhashi and M. Imai)

Effect of Silane Compounds on Catalyst Isospecificity - A Plausible Model Based on MO Calculation (T. Okano, K. Chida, H. Furuhashi, A. Nakano and S. Ueki)

13C NMR Investigation on Lewis Base Activation Effect in High Yield Supported Ziegler-Natta Catalysts (M. C. Sacchi, I. Tritto, C. Shan and L. Noristi)

A New Electron Donor for the Stereospecific Polymerization of Pro- pene (T. Sugano, Y. Yamamoto and T. Fujita)

Formation of Cationic Species and Additive Effect of Ethyl Benzoate on Polymerization of Isobutene and Styrene with TiC13 -Alkylaluminum Catalyst (K. Endo and T. Otsu)

Cop and Terpolymerization of Ethene and Higher a-Olefins with MgH, Supported Ziegler Catalysts : New Mechanistic Insight via the True Reactivity Ratios (G. Fink, W. Fenzl, N. Herfert, T. Muller and I. Jaber)

Co- and Terpolymerization of Ethylene, Propylene and Butadiene with Supported Titanium Catalyst ( S . Lin, Q. Wu and L. Sun)

Kinetics of Ethylene -Propylene Copolymerization over MgClz -Sup- ported Catalysts (S. K. Ihm, K. S. Kang, K. J. Chu and H. S. Chang)

131

139

147

155

165

177

185

20 I

211

223

245

263

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

A Study on the Active Sites of a Primary Type of MgClz-Supported Catalyst by Ethylene-Propylene Copolymerization (M. Terano and K. Ishii)

Syntheses of Terminally Hydroxylated Polyolefins Using Zn (CzH5) and Oxygen as Chain Transfer and Quenching Reagents (T. Shiono, K. Yoshida and K. Soga)

Conversion of Titanacyclobutane Complexes for Ring Opening Metathesis Polymerization into Ziegler-Natta Catalysts (I. Tritto and R. H. Grubbs)

Modification of High cis- 1, 4 Polybutadiene by Neodymium Cata- lyst (I. Hattori, F. Tsutsumi, M. Sakakibara and K. Makmo)

Homo- and Co-polymerization of Ethylene with the Highly Active TiCld/THF/MgClZ Catalyst (I. Kim, M. C. Chung, H. K. Choi, J. H. Kim and S. I. Woo)

Morphology of Nascent Polypropylene Produced by MgClp Supported Ti Catalyst (M. Kakugo, H. Sadatoshi and J. Sakai)

Hafnium Based Catalysts for the Polymerization of Olefins (F. Masi, S. Malquori, L. Barazzoni, F. Menconi, C. Ferrero, A. Moalli and R. In- vernizzi)

High Active Ziegler-Natta Catalysts for Homo- and Copolymeri- zation of Ethylene by Supporting a Grignard Compound and T i c 4 on SiOz (A. Munoz-Escalona, A. Fuentes, J. Liscano and A. Albornoz)

New Solvay SB 12 TiC13 Polypropylene Catalyst (A. Bernard and P. Fiasse)

Polymerization of Cyclic Olefins with Homogeneous Catalysts (W. Kaminsky, A. Bark and I. Dike)

Syndiotactic Propylene Polymerizations with iPr CCpFlulZrClp (J. A. Ewen, M. J. Elder, R. L. Jones, S. Curtis and H. N. Cheng)

Stereospecific Polymerization of a-Olefin with an Ethylene Bis (1 -1ndenyl) Hafnium Dichloride and Methyl- Aluminoxane Catalyst System (M. Kioka, T. Tsutsui, T. Ueda and N. Kashiwa)

277

285

30 1

313

323

345

355

377

405

425

439

483

xvi Contents

34.

35.

36.

37.

38.

Isotactic Polypropylene with a Soluble Metallocene Based Catalyst System - Characterization of Blown Film - (T. Tsutsui, M. Kioka, A. Toyota and N. Kashiwa)

Propylene Polymerization by Stereorigid Metallocene Catalysts : Some New Aspects of the Metallocene Structure/Polypropylene Microstructure Correlation (M. Antberg, V. Dolle, R. Klein, J. Rohrmann, W. Spaleck and A. Winter)

Polymerization of Styrene and Copolymerization of Styrene with Olefin in the Presence of Soluble Ziegler-Natta Catalysts (M. Kakugo, T. Miyatake and K. Mizunuma)

Propylene Polymerizations with Silylene-Bridged Metallocene Catalysts (S. Miya, T. Mise and H. Yamazaki)

Homogeneous Ziegler-Natta Catalysts and Synthesis of Anisotactic and Thermoplastic Elastomeric Poly(propy1ene.s) (J. C. W. Chien, B. Rieger, R. Sugimoto, D. T. Mallin and M. D. Rausch)

493

501

517

53 1

535

Preface

Recent development of a new generation of Ziegler -Natta Catalysts using either magnesium dichloride as carrier or methylaluminoxane as cocatalyst has markedly stimulated the research activity in the field of olefin polymerization. These discoveries have not only yielded economical processes for polyolefin production but also opened the way to a new generation of novel polymers. Moreover, the nature of active species is being clarified well by the effort to simplify catalyst systems. There is no doubt that the exchange of ideas among scientists world-wide working in the same field will contribute to achieving our final goals.

The international symposium on"Recent Developments in Olefin Polymerization Cata1ysts"was held in Tokyo in October 1989. This volume includes 38 papers from the 31 lectures and 18 posters presented at the symposium, which covered the following topics : Overview of super - active homogeneous and heterogeneous catalysts, kinetic profile of olefin polymerization including copolymerization, characterization of catalysts and polymers, methods for the determination of active center concentration, role of Lewis bases on the catalyst isospecificity, polymerization mechanisms, and synthetic pathways for functionalized polyolefins. We believe the contents are well balanced between fundamental research and application as well as between homogeneous and heterogeneous catalyst systems.

We wish to take this opportunity to express our gratitude to all the authors who con- tributed to these proceedings. The excellent service of Kodansha Scientific Ltd. in the production of this book is also gratefully acknowledged.

March 20, 1990 Tominaga Keii Kazuo Soga


1

1. A Theory of Time- Invariant Molecular Weight Distributions in Heterogeneous Ziegler - Natta Polymerizations

Tominaga KEII

Tokyo Institute of Technology, Preparation Committee of JAIST,

Monbusho 7F1, Kasumigaseki 3-2-2, Chiyoda-ku, Tokyo, Japan

Introduction

Molecular weight distributions (MWDs) of produced polymers in

heterogeneous Ziegler-Natta polymerizations have been discussed from

the view points of both fundamental understanding and practical con-

trol.’) The MWDs in the polymerizations are always broader than those

of polymers produced in homogeneous Ziegler-Natta polymerizations, the

reason for which has been pursued for long time as one of the most

important topics from a fundamental view. As is well known, there are

three theories: monomer diffusion contr01,~-~) transfer rate decrease

with chain length5I6) and non-uniform active centers in activity.7t8)

The present author prefers the theory of non-uniform active centers in

propagation rate constant, confirming that there is no effect of

hydrogen addition’,’ on MWDs and that of intermission of polymeriza-

tion on rate-decay during polymerization.’ ’ I No effect of hydrogen addition to the polymerization system on MWD is evidence for the non-

uniform theory, according to Roe’s criteria14) and no effect of poly-

merization interruption on rate-decay means that the polymerization

rate is independent of the amount of polymer, which is evidence refu-

ting monomer diffusion control theory. The diffusion control mechanism

is refuted by Reichert et al. who obtained polymers of broad MWD in a

solution polymerization system.l2) It appears that the non-uniform

center theory is most useful, as reviewed by Zucchini and Cecchin.’)

However, a definitive conclusion has not been reached and the discus-

sion is still open.

In this article, it will be pointed out that the behavior of MWD

of polymers produced at the initial stages of polymerization plays an

2 T. Keii

i m p o r t a n t role fo r t h e above m e c h a n i s t i c d i s c u s s i o n of t h e b r o a d n e s s o f MWDs. S u p p o s i n g i n i t i a l s t a g e s o f p o l y m e r i z a t i o n w h e r e t h e y i e l d and m o l e c u l a r s i z e s o f produced p o l y m e r s are v e r y small, t h e o r i g i n a l c a t a l y s t s u r f a c e may r e m a i n unchanged and t h e d i f f u s i o n c o n t r o l t h e o r y s h o u l d p r e d i c t a n a r r o w M W D b e c a u s e o f t h e a b s e n c e o f a n y room t o t a k e t h e " m u l t i - g r a i n mode l " o r "core mode l " o f t h e d i f f u s i o n c o n t r o l t h e o r y . The c h a i n - l e n g t h t h e o r y p r e d i c t s t h e same c o n c l u s i o n . The non- u n i f o r m c e n t e r s t h e o r y , h o w e v e r , p r e d i c t s b r o a d M W D s e v e n f o r t h e i n i t i a l s t a g e s o f p o l y m e r i z a t i o n .

Such i n i t i a l p o l y m e r i z a t i o n s t a g e s a p p r o p r i a t e d f o r t h i s c r i te - r i o n m u s t b e l o n g t o t h e q u a s i - l i v i n g p o l y m e r i z a t i o n s t a g e of a n y h e t e r o g e n e o u s p o l y m e r i z a t i o n , w h e r e t h e a v e r a g e m o l e c u l a r s i z e i n - creases from a small and t i m e - p r o p o r t i o n a l v a l u e t o a l a r g e s t a t i o n a r y va lue . A few MWDs d u r i n g q u a s i - l i v i n g s t a g e s o f h e t e r o g e n e o u s Z i e g l e r - Natta p o l y m e r i z a t i o n have been r e p o r t e d . The t i m e dependency o f M W D s

r e p o r t e d a re n o t un ique b u t sca t te r , f rom a b r o a d e r t o a narrow,13) or v i c e v e r s a , 1 4 ) and down and up t o s t a t i o n a r y . ' 5, Complex changes are assumed on t h e basis o f changes i n t h e number o f some k i n d s of a c t i v e c e n t e r s . Thus mean ingfu l s t u d i e s on MWDs i n t h e c o u r s e of q u a s i - l i v i n g p o l y m e r i z a t i o n mus t be carried o u t t o g e t h e r w i t h o b s e r v a t i o n of t h e k i n e t i c b e h a v i o r s of p o l y m e r i z a t i o n t h e m s e l v e s . I n t h i s a s p e c t t h e f o l l o w i n g e x p e r i m e n t a l r e s u l t s are u s e f u l .

E x p e r i m e n t a l R e s u l t s o f Q u a s i - l i v i n g P r o p e n e P o l y m e r i z a t i o n w i t h a MgC12-supported T i C l q / A 1 ( C 2 H 5 ) C a t a l y s t

F i g u r e s 1 a n d 2 s u m m a r i z e t h e r e s u l t s r e p o r t e d by t h e p r e s e n t a u t h o r a n d h i s c o w o r k e r s 1 6 , 1 7 ) a n d by K a s h i w a a n d h i s c o w o r k e r s . 1 8 )

The abscissa k t , is t h e d i m e n s i o n l e s s t i m e c a l c u l a t e d w i t h expe r imen- t a l v a l u e of k, t r a n s f e r ra te c o n s t a n t , and t h e o r d i n a t e is t h e norma- l i z e d a v e r a g e m o l e c u l a r s i z e ( w e i g h t ) , n/n,, w i t h t h e u s e o f expe r ime- n t a l s t a t i o n a r y v a l u e , Em. The e x p e r i m e n t a l v a l u e s o f t h e c o n s t a n t s have been o b t a i n e d by means o f t h e e q u a t i o n 1 3 )

- -

which is a p p l i c a b l e t o p o l y m e r i z a t i o n s w i t h c o n s t a n t rates o f propaga- t i o n and t r a n s f e r .

The y i e l d o f p o l y m e r s f o r s h o r t p o l y m e r i z a t i o n t i m e , e.g., Y =

220 g / m o l - T i f o r 0.1 s i n t h e case o f M g C l 2 - s u p p O r t e d c a t a l y s t , " )

1. A Themy of Time-Invariant MWD in Ziegler-Natta Polymerization 3

1

8 t

I I

15 0.5

C

0 4

#- - No

k I 1 1

c* 20

I I 10

C l I N

v

a 1

8 C ~

lX - 0.5 IL

C

0 0 1 2 3 4 5

k t

Figure 2.

propene.

MgC12/TiC14 - TEAIEB, 10 OC.

0: Styrene, k = 2.40 min-’.

A: 1-Butene, k = 1.37 min-l.

Moleclar weights during quasi-living polymerization of

4 T. Keii

corresponds to a small amount of polymers per catalyst weight such as

0.1 g/g-cat. It should be noted that the polymers of small amount

showed a large polydispersity, 4, contrary to the expectation from the

diffusion limitation theory. The most remarkable of the above experi-

mental results is that the observed large polydispersity values remain

unchanged during these quasi-living stages of polymerizations, i.e.

the existence of time-invariant broad M W D s during living polyme-

rization stages. This new result of M W D s , if limited in the above

experiments, adds a new aspect to the discussion of the foregoing

three theories which have been developed for stationary M W D s . In the

light of this new result it is clear that all three theories have some

defects; these are noted as below.

As described above, small amounts of polymers produced can be

considered insufficient to assume a "multi-grain model." However, the

experimental fact that the polymers produced at 0.1 s are almost (90%)

living and their number average molecular size is 80 may give us a

modified model of diffusion control such that monomer diffusion to

polymerization center is affected by even a short living polymer. To

construct such model for this experimental fact may not be difficult.

Such a model, however, must explain also that further growing of

living polymer to 800 in average size and accumulation of dead poly-

mers do not further affect the monomer diffusion rate, in order to

explain the time-invariant nature of experimental MWD. The experimen-

tal result that at 0.1 s the transferred (dead) polymer comprises only

1 0 % with the remaining ones living does not fit the theory of chain-

length dependent transfer rate. Thus these two theories may not be

applicable to the experimental results. On the other hand, the theory

of non-uniform (propagation rate constant, k ) polymerization centers

can explain the large values of polydispersity in polymerizations of

such short time that the polymerizations can be regarded as living,

because the polydispersity can be expressed by

P

where <k > designates center averaged value. The polydispersity value

is always larger than unity in accordance with the non-uniformity of

the k value of catalyst. However, with increasing polymerization time

the value of polydispersity should approach the following stationary

one

P

P

1. A Theory of Time-Invariant MWD in Zieglm-Natta Polymeniation 5

That is, the non-uniform theory also cannot explain the observed time-

invariant nature of the MWDs.

To this situation the present author proposes here an effective

modification of the non-uniform center theory as follows.

Theory of Intrinsic Fluctuation of Surface Reaction

A growing polymer chain on the catalyst surface may react with

one of its neighbors. For example, one of the monomers coordinated

(adsorbed) on a neighboring Ti can be inserted into the Ti-C bond of

the growing polymer chain in accordance with its reactivity. The

nearest neighbor monomer may be the most easily inserted while the

next nearest monomer may be less easy to insert and a monomer on more

distant Ti may be inserted with difficulty, which is the essential

difference in homogeneous polymerization. If it is, the rate of

insertion reaction of a growing chain must be the sum of possible

combinations with its neighboring monomers. At the same time, the

transfer reaction of a growing chain occurs with one of its neighbo-

ring species (monomer or some other transfer reagent); then the tran-

sfer rate of a growing chain also must be the sum of combinations with

its neighbors. The number of neighboring sites of a growing chain on

a crystal surface increases with distance from the site of the growing

chain. We assume that the probability of a combination of a growing

chain and a specified neighbor, the reactivity of which is kp or k,

can be expressed in terms of its probability density function by

where

and transfer reaction of a growing chain.

and k are the neighbor average rate constants of propagation

NOW, we take the usual polymerization mechanism in the case of

rapid initiation where the total number of polymerization centers

(growing chains) is kept constant, as follows.

P

kP growing reaction: M*n-1 - M*n (5)

k transfer reaction: M*n - M*, + Mn (6)

6 T. Keii

where we abbreviate kp[Ml by kp.

The above mechanism can be applied to the pair of two active

sites characterized by k and k, one of which is horsed by a growing

chain. For the pair of such active sites, the following differential

equations hold for the number of growing chains of molecular size n,

P

* * * n'

dN ./dt = kpN n-l - (kp + k)N*, n > 2 (7)

m * Using the notations; 2 N * ~ = c o, k /k = y and

the following Laplace transformation

kt = 'I, and applying n=l

to (7) and ( 8 1 , we have

Applying the inverse Laplace transformation for the above, the solu-

tion f o r the differential equations (7) and ( 8 ) can be given and

However, we can immediately obtain the averaged value, N*,, averaged over all combinations with neighbors. --

noting that

- m

N*, =LN*,exp( -k/E)dk/E = (1 /T$N*,

as

where fi = rpt/(l + Ft). The corresponding polymers, Nn, is given as below.

* dNn/dt = kN

(11)

(12)

- value, Nn, of the dead

(13)

Applying the same Laplace transformation, we have

1. A Themy of Time-Invrrriant MWD in Ziegler-Natta Polyme7ixafiOn 7

-7 - Nn = ktN (14)

From the results (12) and (14) we have the frequency probability, in

terms of its density function F(n),

the number average molecular size

and the weight average molecular size

Then, the polydispersity in this case has the time-invariant value of

2.

The time-invariant nature of MWD in this case is clearly shown by the

form of (15) or by its GPC curve, W(1og n) against log n, as that

the form of which is only lateral shift by log;

in accordance with change of time.

or log(Et/(l + xt))

Non-uniformity of Propagation Rate Constant

As described above, the intrinsic fluctuation of surface reaction

can explain the time-invariant nature of MWDs in the heterogeneous

Ziegler-Natta polymerization but not the broadness (Q > 2) of MWDs. AS

reported before, observed decays of polymerization rate by CO poiso-

ning in the gas phase propene polymerization with a MgC12-supported

catalyst or TiC13 catalyst could easily be understood on the basis of

Then we assume that the active sites on the non-uniformity of k 'l) P'

8 T. Keii

surface of a catalyst constitute plural kinds of different kp value. Simply put, it corresponds to the surface of a polycrystal on which

many crystal planes are exposed. For such a case we may apply the

following formalism using a surface distribution density function, - g(kp) 8

- - - - - <N*,> = J(k/kpf(t) )exp(-nk/kpf(t))g(kp)dkp (20)

S o we have the resultant average molecular sizes

w h i c h gives t i me- i nva r ian t po 1 y di s pe r s i t y

Here, it should be noted that the invariant nature of this polydisper-

sity is closely related to the assumption that the k value is a

constant common tc active sites. Few data to discuss this assumption

have been reported, though Kashiwa”) reported that the heptane inso-

luble polypropylene and soluble fraction showed different values of

2100-6300 (l/mol s ) and 350-1000 (l/mol s ) , while the same value

of k, 0.33 s - ’ , was found in the polymerization with MgC12/A1(C2H5)3/

TiC14/ethyl benzoate catalyst at 60 OC.

Here, of MWD, in terms of GPCcurve, is

illustrated in Fig. 3 for a case with two kinds of active centers:

<t > = 1000, Fp,l = 2035, kp12 = 370 (l/mol s ) , [MI = 0.73 mol/l, k = P 1 s-l and C*o,l / C*o,2 =2/3. The calculated curves for t = 0.1 , 1 and

s show the invariant nature of MWD, and that a broadness of Q = 3.7

and the appearance of a small shoulder at higher molecular region, the

natural result of the synthesis of the component GPC curves for the

two polymer fractions of the total polymers.

The more important expectation from this theory of non-uniform

surface is how the value of polydispersity changes. The Q value-

determining factor is the broadness of k distribution of the surface

kP‘

- -

P

1. A Themy of Time-Invariant MWD in Ziegler-Natta PolpnmiaatMn 9

1-0.1s 1=1s 1 - 0 I

10 100 1000 n

Figure 3. Time-invariant MWD calculatd on the basis of a non-uniform

surface (two-center model).

of catalyst, as can be seen from (20). The calculated results from the

previous report are in agreement with this. The CO poisoning experi-

ment gave a surface distribution density function

g(kp) = c0ns.r-B P (24)

for MgC12-supported catalyst with B = 2 and for TiC13/A1(C2H5)2C1

with 1.5. The MWDs in the polymerization with the traditional TiC13

are always broader in conformity of its smaller value of 6. In addi-

tion, it was shown that the application of the function (24) with B = 2 for stationary MWD, which corresponds to (20) in the case of f(t) = 1 ,

resulted in a Wesslau type (lognormal) MWD. The same result can then

be obtained for MWDs during quasi-living polymerization by (20) with

f(t) < 1 . A s shown in Fig. 2, the polystylene showed a very large

polydispersity value, Q = 15. This result may be considered approxi-

mate as only 13% of the total active sites have relatively high acti-

vity.

Acknowledgment

The author expresses heartfelt gratitude to Mr. K. Nakamura and

the governmental staff of the preparation committee of the new gra-

duate school, Japan Advanced Institute of Science and Technology, for

10 T. Keii

t h e i r w a r m encouragemen t a n d c o o p e r a t i o n even a s h e c o n d u c t e d o u t s i d e work a s a committee c h a i r m a n f o r t h e i n t e r n a t i o n a l s y m p o s i u m w h i c h gave r ise t o t h e s e p r o c e e d i n g s .

R e f e r e n c e s 1. U. Z u c c h i n i a n d G. C e c c h i n , Adv. Polym. S c i . , 5 l , 101 (1983).

2. V. W. B u l s a n d T. L. H i g g i n s , J. Polym. S c i . P a r t A - 1 , g , 1025 (1 970).

3. W. R. S c h m e a l a n d L. R. S t r e a t , AIChE. J., l7, 1188 (1971).

4. W. H. Ray, " T r a n s i t i o n Metal C a t a l y t i c P o l y m e r i z a t i o n s , Ziegler- Na t t a a n d M e t h a t h e s i s P o l y m e r i z a t i o n s " ed . R. P. Q u i r k , p.563 (1 988). ( P r o c e e d i n g of M M I Congres s 1981 ) Cambridge Univ. Press.

5. M. Gordon a n d R . - J . Roe, P o l y m e r , 2, 41 (1 961 1. 6. R.-J . Roe, P o l y m e r , 2, 60 (1961).

7. A. C l a r k a n d G. C. B a i l e y , J. Cata l . , 2, 230, 241 (1963).

8. G. Nat ta , J. Polym. S c i . , 34, 21 (1959).

9. T. Keii, e t al., P r e p r i n t IUPAC 28, Macromol. Symposium, Amherst , Ma., J u l y 12-16, p.2371.

10. T. K e i i , e t a l . , Makromol. Chem., 185, 1537 (1984). 11. T. K e i i , e t a l . , Makromol. Chem., 183, 2285 (1982). 12. H. Meyer a n d M. H. R e i c h e r t , Angew. Makromol. Chem., 57, 211

13. H. S c h n e c k o , K. A. J u n g , a n d W. K e r n , " C o o r d i n a t i o n P o l y m e r i z a - (1977).

t i o n " ed. C h i e n , p.73 (1975).

14. G. B i e r , e t a l . , Makromol Chem., 5 8 , 1 (1962).

15. K. A. Jung a n d H. S c h n e c k o , Makromol. Chem., 154, 227 (1972). 16. T. K e i i , M. T e r a n o , K. K i m u r a , a n d K. I s h i i , Makromol. Chem. R a p i d

Comm. , s, 583 (1987). 17. M. T e r a n o a n d T. K e i i , Unpub l i shed d a t a . 18. N. Kashiwa and J. Yosh i t ake , Polymer B u l l e t i n , 11, 485 (1984).

11

2. Studies on the Polymerization of Propylene Using Highly Ac- tive Magnesium Chloride Supported Ziegler-Natta Catalysts : Effects of Alkyl Concentration on the Polymerization Rate and on the Active Centre Concentration

P.J.T. TAIT, and I.A. JABER

Chemistry Department, UMIST, Manchester,

M60 1QD. England, U.K.

A.J. LOONTJENS

DSM, Research and Patents, Geleen, Holland.

ABSTRACT

Highly active MgC12 - supported TiC14 Ziegler-Natta catalysts were used for propylene polymerization and the effect of varying the triethylaluminium

concentration was studied in relation to the polymerization rate and to the number

of active centres. Active centre concentrations were carried out using I4C - labelled carbon monoxide. An optimum A1Et3:Ti molar ratio was found to be

necessary in order to obtain the highest rates of polymerization and the highest

active centre concentrations. The concentration of active centres, C*, remains

more or less constant with polymerization time, but the average propagation rate

coefficient, L both C* and

P 4.4 - 6.6 mol % of the total titanium was active. The dependence of the maximum

values of the rates of polymerization on the alkylaluminium concentrations were

investigated using Langmuir-Hinshelwood isotherms.

decreases. For A1Et3:Ti molar ratios greater than 80:l values of P' decrease only slightly with increase in A1Et3:Ti molar ratio. Only

INTRODUCTION

The most commonly and effectively used metal alkyls for propylene

polymerization employing magnesium chloride - supported catalysts are invariably trialkylaluminium compounds, dialkylaluminium halide compounds giving much lower

activities. In general the polymerization kinetics shown by catalysts of this type

are strongly affected both by the trialkylaluminium to titanium ratio and by the

type of alkylaluminium compounds which is used.

One important feature of ball-milled magnesium chloride-supported catalysts

employing ethyl benzoate (EB) as an internal donor is that they often exhibit very

12 P. J. T. Tait, I. A. Jaber and A. J. Loontjens

high initial rates of polymerization which decrease rapidly with time. This type

of behaviour has been reported by many workers for the polymerization of propylene

(1 - 6 ) . The decay of the polymerization rate with time has been subjected to many

kinetic studies. Whilst the rapid decrease in the rate of polymerization was

initially attributed to the monomer having to diffuse through an ever increasing

thickness of polymer layer covering the catalyst surface (7 ,8 ) , it has been shown

that deactivation occurs when a catalyst is aged in the absence of monomer where

no additional polymer is being formed (1,9,10).

Doi et a1 (9) using a MgC12 - supported catalyst showed that the decay rate was second order with respect to catalyst activity. Brocheier ( 5 ) has reported an

order of 1.5, whilst Tait and Wang ( 6 ) have demonstrated that the decay can be

better

models which were considered.

represented by a multi-centre first order decay model than by other

Variation of the trialkylaluminium concentration can bring about considerable

changes in the rate-time profiles for MgCl, - supported catalysts. The changes observed are quite complex and are believed to arise from simultaneous adsorption

and reduction reactions (11).

In general, as is shown by the results of the present investigation, the rate

of polymerization initially increases with increase in the trialkylaluminium to

titanium ratio. However, as the trialkylaluminium to Ti ratio increases above an

optimum value the rate of polymerization decreases with a simultaneous decrease in

stereospecificity. The initial increase in rate with increase in trialkylaluminium

concentration at constant titanium concentration is believed to be due to the

continual activation of potential catalytic centres. The decrease in the rate of

polymerization at higher trialkylaluminium concentrations is due according to

some workers (11 - 15) to adsorption of trialkylaluminium on catalytic centres in competition with monomer. Other workers attribute such a decay to an

over-reduction of titanium (16, 17).

In order to obtain a better understanding of the effects of trialkylaluminium

on the ratio of propylene polymerization, the number of active centres, C*, was

determined using a 14C0 - radio - labelling technique and the propagation rate coefficient, k was then evaluated.

P'

EXPERIMENTAL

Catalysts.

The MgCl -supported high activity catalysts were supplied by DSM, Geleen, Holland.

Results for two different catalysts, Cat-E and Cat-F, are reported in this paper.

Both catalysts were of a ball-milled type, MgC12/ethyl benzoate/TiC14, and

contained 2.5 wt% Ti.

2

2. Effect ofAEt3 Cacentmfion on Number of Active Centen 13

Active Centre Determination.

A radio-labelling technique using 14C0 was used for the determination of

active centre concentrations.

When performing active centre determinations in the presence of monomer a

specified amount of 14C0 was injected into the polymerization reactor using a gas

tight syringe. A volume of 10 cm3 14C0 was used in the present determinations.

Upon addition of 14C0 polymerization ceased within about 3-5 min. The 14C0 was

then left to interact with the catalyst system for a chosen length of time, tc,

the contact time, before the contents of polymerization reactor were transferred

into a mixture (volume ratio 19:l) of methanol and conc. hydrochloric acid (300 3

cm ) .

Where experiments for active centre determinations were carried out in the

absence of monomer, the propylene supply was stopped and the reactor evacuated

several times, each time with the admittance of dried nitrogen. Finally, the

reactor was pressurised with dried nitrogen and 14C0 introduced. At the end of the

contact time the polymer slurry was transferred into acidified methanol. The

radio-labelled polymer was then filtered, washed with acidified methanol ( 3 x 100

cm ) and oven dried at 60 OC.

scintillation counter calibrated using 14C - toluene and chloroform.

3

The radio-counting procedure was carried out using a TRI-CARB 300C liquid

The measured radioactive content of the polymer, Ci, in mol I4CO per mol Ti

is given by

C. = GA/a (1)

where G is the polymer yield in g polymer per mol Ti, A is the polymer activity in

d.p.m. per g (1 d.p.m. = 60 Bq) and a is the specific activity of the I4CO in

d.p.m. per mol . When the carbon monoxide inserts into all active transition-metal bonds

during the selected contact time between carbon monoxide and active centres, tc,

and where multiple insertions do not take place, and where only one polymer chain

grows from each transition-metal atom, the active centre concentration, C*, in mol

per mol Ti is given by

c* = ‘i ( 2 )

RESULTS AND DISCUSSIONS

Rate-time profiles.

A typical rate-time plot for the polymerization of propylene using a

ball-milled catalyst of the type MgC12/EB/TiC14 - Al(i-Bu)3/EB is shown in Figure

1. These polymerizations have no so-called induction period and the rate of

polymerization shows an initial maximum value which decreases rapidly with


Reagents.

Triethylaluminium. Neat triethylaluminium was supplied by ICI PLC, Wilton,

England,. U.K., and was diluted with distilled dried EC180, and used without

further purification.

Methyl-p-toluate (MPTL. This was supplied by Fluka, AG., and had a purity of 99%.

Solutions in EC180 were prepared and purged with dry nitrogen. MPT was used as the

external donor in the present investigation.

EC 180. This hydrocarbon solvent was used as the polymerization medium and was

supplied by ICI, PLC. EC-180 is a mixture of the highly branched hydrocarbons

2,2,4,4,6-~entamethylheptane and 2,2,4,6,6-~entamethylheptane having a boiling

range of 175-180 OC at 1 atm pressure. Before use the EC180 was dried over

preactivated molecular sieves, type 4A, for at least 24 h.

Propylene. Polymerization grade propylene, 99.5% pure, was supplied by ICI, PLC,

and was dried by passing through two columns (1.0 m x 2.5 cm) of preactivated

molecular sieves, types 13X and 4A.

14C-Labelled carbon monoxide. I4CO was supplied by ICI, PLC, as a mixture with 3 normal carbon monoxide in a 1.0 dm cylinder under a pressure 3 atm and had an

activity of 1.0 mCi.

Polymerization Procedure. 3 All polymerization runs were carried out in a 1 dm glass jacketed reactor

equipped with an efficient stirrer operated at 800 - 1200 rpm. 500 cm' EC180 was

used as diluent. Polymerizations were normally conducted under 1 atm pressure of

propylene and at 60 OC. The polymerization temperature was controlled by pumping

water from a thermostated bath through the reactor jacket. The EC180 was refluxed

3-4 times under vacuum prior to the start of a polymerization. Propylene was then

admitted to the reactor and polymerization started by the addition of the

catalytic components. In the case of a three component catalytic system the order

of addition was:

electron donor were diluted with EC180 and the catalyst stored as a slurry in

EC180. The catalyst components were introduced into the reactor by means of glass

syringes fitted with stainless steel needles. A pulse flow controller was used to

measure the consumption of propylene. At the end of a polymerization run the

polymer slurry was removed through the reactor outlet employing a positive

nitrogen pressure. The polymer was then quenched with isopropanol, filtered and

dried at 70 OC overnight. The isotactic index (1.1.) of the polymer was determined

by Soxhlet extraction with boiling n-heptane for 24 h.

A1Et3; electron donor; and finally the catalyst. The A1Et3 and

2. Effect of AEt3 C0nc;entration MI Number of Actiw Centers 15

polymerization time. The catalysts, used for the present study, showed a somewhat

different type of polymerization behaviour, as is shown in Figure 2 for Cat-E.

r 1 1

250

500 -

0 50 100 150 200

Polymorlrallon lime I m h

Figure 1. Typical plot of instantaneous rate of polymerizations, R for the

polymerization of propylene in EC180 at 60 OC using the catalyst system

MgC12/EB/TiC14 - Al(i-Bu)3/EB. [Ti] = 0.0327 mnol d n ~ - ~ ; [All : [Ti] = 810 : 1 ;

(All : [EB] = 5.7:l.

P'

I

r I I I I

80 120 Polyrnerizalmn time I min

Figure 2. Plots of instantaneous rates of polymerization, Rp, for the

polymerization of propylene in EC180 for various AlEt :Ti &la= ratios at 60 OC

using Cat-E. [Ti] = 0.013 ml d ~ n - ~ ; [MPT] = 0.20 mnol d n ~ - ~ ; [C3H6] = 0.232 mol 3

dm-3.


The rate of polymerization increases rapidly with polymerization time for

A1:Ti > 58:1, reaching a maximum value in 2-6 min, depending on the A1:Ti molar

ratio. Thereafter the rate of polymerization decreases with the polymerization

time. At lower A1:Ti molar ratios, i.e., A1:Ti = 38:1, much lower activity is

obtained, although the rate-time profile shows good stability.

It is evident from Figure 2 that the decrease in the rate of polymerization

is dependent on the triethylaluminium concentration at constant catalyst

concentration. These rate-time plots are in some ways similar to those obtained

using spherical type magnesium chloride supports, although the latter class of

catalysts shows a greater time stability.

Effect of triethylaluminium to titanium molar ratio

The effects of triethylaluminium to titanium molar ratio on the maximum rates

of polymerization are shown in Table 1.

Table 1.

polymerization activity of Cat-E at 60 'C.

Effect of triethylaluminium to titanium molar ratio on the

I I

I [ AlEt3 1 / Rp (max.) / R P (aver.) / I

1.1. 9 pp 9pp Decay m l Ti h atm mmol Ti h atm Index

I

I I 38

I 58

I 77

I 97

I 117

I 135

I 154

I 194

I I

- 1190

1080

1280

1380

1350

1420

1500

65

640

7 10

730

720

700

670

640

1.60

2.33

3.03

3.29

4.00

4.77

4.74

6.20

--I

I - I

90.1 I 90.3 I

90.3 I

94.0 I

86.0 I

88.0 I 84.0 I

I I

[Ti] = 0.013 mmol dm-3;

EC180 = 0.500 dm3;

[MPT] = 0.20 mmol dmV3;

[C3H6] = 0.232 mol dm-3 (1 atm pressure).

2. Ejject of AEt3 ConCentraiiOn on Number of Active Centers 17

On increasing the triethylaluminium concentration at constant catalyst and at

constant external donor (MPT) concentration the maximum polymerization rate (R ( m a ) = maximum polymerization rate occurring during the early stages of

polymerization, i.e., 2 - 6 min) first increases rapidly but then reaches more or

less a constant value, while the average rate of polymerization (R (av) = average

rate of production of polymer over the duration of polymerization, i.e., 2 h)

first increases sharply, reaches a maximum value, and then decreases. As is also evident the decay index (equal to R (max)/R (240 min) ) increases with increase

P P in A1:Ti molar ratio, indicating progressive over-reduction of the titanium.

P

P

Active centre concentrations

The effect on the rate of polymerization of addition of various amounts of CO

to a polymerization system is shown in Figure 3 .

Vol o f CO injettod - o = O c m ’

100 -

“ Pme /mn 0 80 120

Figure 3.

addition of various amounts of CO to a propylene polymerization employing a

MgC12/ED/TiC14 catalyst at 60 OC (18).

[Ti] = 0.080 ml d ~ n - ~ ; [AlEt,] : [DPDMS] : [Ti] = 169:16.9:1; EC180 = 0.250 dm3;

[ C H ] = 0.232 m o l dm-,.

Plot of polymerization rate versus time showing effect of

3 6


As is evident from an inspection of Figure 3 there is a dramatic drop

in the rkte of polymerization on addition of carbon monoxide such that for

volumes of greater than 1 cm3 the polymerization rate drops to a zero value

within 7 min of addition. No recovery in the polymerization rate occurs

during the subsequent period of observation (70 min) and complete

inhibition of polymerization has taken place.

The addition of 14C0 to a polymerization system is believed to lead to

the following reactions:

l4c0

P + P Cat 5 P + l4c0 + Cat\ P + Cat - c % P

I 0 ( 3 )

The subsequent addition of acidified alcohol would then give :

H+ P Cat - 14C 5 P + ROH + H - 14C 5 P + CatOR

U II 0 0 ( 4 )

where 0 represents a vacant coordination site and 5P a growing polymer chain.

However in spite of the apparent simplicity of this method some

uncertainty exists concerning its accuracy (11). It has been observed that the

radioactivity of the final polymer increases with increase in contact time tc(19).

This increase has been variously ascribed to slow initiation and/or multiple

site activity and will be discussed later.

the use of 14C0-radio-labelling the method was used for active centre

determination in the present polymerization system.

In order to gain a better understanding of the problems involved in

Equation (1) was used to calculate values of Ci from the determined

values of A for different contact times. The results shown for catalyst-E

are shown in Figure 4.

2. Effect of AEt3 Gmcenhatimr on Number of Active Centers 19

c** 102 m& molli

0 @

10

0 @

A

A

2 -

I I 1 I

120 240 3 60 Contact lime lmin

Figure 4.

monomer -0-, or nitrogen -A-.

[Ti] = 0.065 mmol 3

EC180 = 0.200 dm ; temperature = 60 OC; [ C H ] = 0.232 m o l dm-3 (1 atm pressure).

Plot of C. versus contact time for Cat-E in the presence of

[A1Et3] : [Ti] = 77:l ; polymerization time = 10 min;

3 6

The results plotted in Figure 4 show the following.

(i) An initial value of C. both in the presence and absence of propylene

(nitrogen present), even at very short contact times, i.e., tc = 5 min.

(ii) An increasing value of C . as t increases from 5 min to about 120 min. The

increase of Ci is more iarkedcfor I4CO addition in the presence of

propylene, where the increase is by a factor of 2.15.

(iii)C. reaching a more or less limiting value at longer t values, i.e.,

tc = 120 - 240 min both in the presence of propylene and in the presence of

nitrogen.

(iv) Higher values of C . for determinations carried out in the presence of

propylene both for short and long t values.

Any interpretation of these results must take into account the results shown

in Figure 3 .


From an examination of Figure 3 it is evident that complete inhibition of

polymerization takes place within a few minutes (t = 5 min) following addition of

carbon monoxide to polymerization systems (propylene present), presumably by rapid

complexation of the carbon monoxide with vacant sites. An examination of Figure 4

shows that for the addition of 14C0 in the absence of propylene (nitrogen present)

insertion of 14C0 occurs within 5 min to about 50% of the final value obtained

after 6 h. However the question as to whether this insertion takes place only on

centres which are highly active or whether the insertion reaction itself is

incomplete is still unanswered and awaits further experimentation. However the

same difficulty evidently exists in the use of I4CO for active centre

determination with high activity catalysts as has been reported for catalysts of

the type 6-TiC13.0.33A1C13 (19). Additionally for catalysts of the latter type it

has been established that carbon monoxide can be consumed in side reactions

involving adsorbed aluminium alkyl (20).

C

While the plots of C. versus contact time both in the presence and absence of

propylene show similar trends the reactions involved require different

interpretations.

In the presence of propylene some slow copolymerization of CO is believed to

take place (19, 21) resulting in more than one radio-labelled unit per growing

chain and leading to artificially high apparent values of C*. For this reason it

is believed that Ci values in the presence of propylene for short t

more accurately related to C* values, provided t is at least sufficiently long

for complete insertion of 14C0 to take place. Thys procedure would obviate other

known side reactions (20) and is also consistent with results obtained for

metallocene-aluminoxane systems (22). Such a procedure may nevertheless lead to an

underestimate of the real C* value where the insertion of adsorbed 14C0 is either

slow, i.e., for centres of low activity, or incomplete.

14C0 radio-labelling in the absence of propylene was undertaken specifically

values can be

to eliminate these complications, and for this reason the lower values of C

obtained, particularly at short tc values in the absence of propylene and in the

presence of nitrogen, were puzzling. These lower values could arise from the

elimination of highly active centres which would otherwise have been stabilized by

the presence of propylene or by the destruction of highly active centres due to

the admittance of trace impurities.

i

It is interesting to note that the value of C. for high values of t (i.e.,

>120 min) in the absence of propylene is more or less the same as that of Ci at

2. Effect of AEt3 c0U;entratbn on Number of Active Centers 21

low t values (i.e., 2-5 min) in the presence of propylene. The presence of

propylene evidently serves to activate slower centres for more rapid insertion of

complexed 14C0. Thus it now seems that both methods may be used for the estimation

of active centre concentrations provided the correct precautions and analytical

procedures are followed. Further research is being carried out and will be

published elsewhere.

Values of C* determined both in the presence and absence of propylene for

various contact times are listed in Table 2 together with corresponding average

values of rate coefficients, Ep, determined from the equation

R = k [MI C* P P

0 Table 2. Variation of C* and with contact time for Cat-E at 6 C P

I 1

I Notes Contact time/ c* x lo2 / E / I 3 p-1 -1 I min mol/mol Ti dm mol s I

I I

I 5

I In the 10

I presence 20

I 80

I 120

I of propylene 40

4.4

6.6

7.2

9.2

10.4

11.0

228

162

135

105

94

87

I 210 11.1 93 I I 360 11.6 77 I

I I I I 5

I In the 10

I absence 20

I (nitrogen 80

I present) 120

I 210

I of propylene 4~

I 360

2.7

3.0

3.5

4.0

4.4

4.8

4.7

6.1

233

205

192

165

147

145

137 I 110 I

[Ti] = 0.065 mmol dn~-~;[AlEt~]:[Ti] = 77:l; EC-180 = 0.200 dm3;

[C H ] = 0.232 mol dm-3 (1 a h pressure); polymerization time = 10 min. 3 6


It is apparent from an examination of Table 2 that only a small percentage of

the available titanium is active in polymerization, even in these high activity

catalysts. If the arguments which have been developed are correct then a value for

Cat-E of C* = 4.4 - 6.6 wt% Ti for determinations in the presence of propylene for t

determinations in the absence of propylene (presence of nitrogen) for t = 120 - 360 min. However, this percentage is higher than that in catalysts of the type

6-TiC13.0.33A1C13. The table also illustrates the need when using the present

technique to specify the contact time used, and also to state whether or not the

radio-labelling is carried out in the absence or the presence of monomer.

= 5-10 min has to be compared with a value of 4.8 - 6.1 wt% Ti for

C

Variation of C* within polwnerization runs

One advantage of the use of I4CO - radio-labelling for active centre determinations is that the method allows determination of C* during the course of

a polymerization. Values of C* as a function of polymerization time are shown in

Figure 5 .

C'x lo*/ 6.0

mol 5 .O

molTi -

150

100 iip I

dm3 mol s -

50

Figure 5. Plot of C* and E against polymerization time for Cat-F at 60 OC. P

Determinations carried out in the presence of propylene with tc = 10 min.

[Ti) = 0.04 mnol d ~ n - ~ ; [A1Et3] : [Ti] = 48:l ; EC180 = 0.250 dm3;

[C3H6] = 0.232 mol dm -3 .

2. Effecf of AEi3 Concentration on Number of Active Centen 23

As is evident from Figure 5, the value of C* for Cat-F remains more or less

constant throughout the polymerization at about 5 mol% Ti. The value of however

decreases progressively with polymerization time, an observation first reported by

Giannini (2). this decrease in intrinsic activity is most likely due to some

ligand rearrangement reaction or to a change in valency state of the transition

metal.

P

Variation of C* with triethylaluminium to titanium molar ratio

The variation of C* with the A1Et3 : Ti molar ratio was investigated and

typical results are shown in Figure 6 .

5 .O

C.XlO*/ 4.0

m A molf i

3 .O

2.0 d

- 200 kp '

d m3 mol s

100

50 150 250 AIEt3/Ti molar ratio

Figure 6. Plots of C* and E versus A1Et3 : Ti molar ratios for Cat-E at 60 OC. P

Apart from some initial scatter of values of C* and corresponding E values P

for low AlEt :Ti molar ratios, i.e., <75:1, both C* and decrease only slightly

with increase in AlEt :Ti molar ratios in the region 100 - 250 : 1. For this

reason the decrease in R ( m a ) which is observed with increase in A1Et3.Ti molar

ratio must be largely related to competitive adsorption reactions between monomer

and alkylaluminium active centres as has been detailed by Tait et a1 (12) for

first generation catalyst systems, viz.,

3 P

3

P

24 P. J. T. Tait. I. A. Jaber and A. J. Loontjens

7 Cat % P

7 Cat % P

M

t

Cat 1 P 54 A

+ M 7

A

t

Cat 5 P KA L 7 + A (7)

Dependence of R ( m a ) on triethvlaluminium concentration Y

The dependence of the instantaneous maximum polymerization rate on the was

studied using two models based on the Langmuir-Hinshelwood isotherm, one used by

Keii et a1 (1) and the other by Tait et a1 (12).

The equation derived by Keii et a1 is of the form

R P

where

k = Ep C* %[MI

Rearrangement of equation ( 8 ) into a linear form yields

t Hence a plot of ([A]/R ) versus [ A ] should give a straight line plot of intercept

l/(kKA)' and slope KA/(kKA)'. Such a plot is shown in Figure 7 which shows plots

for R ( m a ) together with plots for a variety of polymerization times for P

comparison.

P

2. Effect of A1Et3 Cacentmtion an Number of Active Centers 25

010 - TIME/ rnln.

( lA I /Rp) l /Z /

*= 10

0.06

0.02 -

I I 1 I

0.6 1.2 1 .u 2 4 [AIEtjl I rnrnol drn-3

Figure 7. Plot of ([A]/R ) t versus triethylaluminium concentration at various 0

P polymerization times for Cat-E at 60 C.

[Ti] = 0.013 ml d ~ n - ~ ; [MPT] = 0.20 mmal d ~ n - ~ ; EC180 = 0.500 dm3;

[C3H6] = 0.232 mol dm-3.

Although some deviation from linearity is evident at low triethylaluminium

concentrations these plots indicate that there is good agreement with the model.

It should be noted that the values of alkyl concentration required in equation

(10) are the equilibrium values and these will differ substantially from the

values at the beginning of the polymerization for low alkyl concentrations.

The equation derived from the Tait model is of the form

Consequently a plot of 1/R

Figure 8 .

versus [A] should be linear. Such a plot is shown in P


5 .O

l o 3 (I/Rpl I

mrnolli h atm

0 PP

3 .O

1 .o

. i 121 B = Bc

A = 2c e = 10 Q = 5

Q i 60

: I marl

1 I I I

0.6 1 .z 1.8 2 . 4 I A l E t j 1 I rnrnol drn-3

Figure 8. Plot of 1/R versus triethylaluminium concentration at various

polymerization times for Cat-E at 6OoC.

[Ti] = 0.013 m l d ~ n - ~ ; [MPT] = 0.20 mmol dm-3;

[C3H6] = 0.232 mol dm-3.

P

EC180 = 0.500 dm3;

Whilst these plots are not particularly sensitive they do indicate that the

decrease in R (max) with increase in triethylaluminium concentration at constant

catalyst and external donor concentration arises mainly from competitive

adsorption reactions.

P

CONCLUSIONS

The rate of polymerization of propylene by means of a highly active catalyst

system, MgClZ/EB/TiCl4 - A1Et3/MPT, has been shown to be dependent on the A1Et3 : Ti molar ratio at constant catalyst concentration.

Determination of active centre concentration by means of a 14C0 - radio - labelling technique both in the presence and in the absence of propylene has

allowed evaluation of C*, yielding similar values when appropriate procedures

are used.

Values of C* equal to 4.4 - 6.6 wt % Ti were established.

After an initial settling period the value of C* decreased only very slightly

with polymerization time within a given polymerization.

The average propagation rate coefficient was found to decrease during the

polymerization time.

After an initial settling period values of both C* and decreased only

slightly with increase in the A1Et3:Ti molar ratio.

This decrease in polymerization rate is consistent with a model involving

competitive adsorption of triethylaluminium.

P

2. Effect of AIE?, Concentration on Number of Active Centers 27

ACKNOWLEDGEMENTS

Thanks are expressed to DSM for financial support.

REFERENCES

1.

2.

3.

4.

5.

6 .

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

T. Keii, E. Suzuki, M . Tamura, M . Murata, and Y. M i , Makromol. Chem., 183, 2285 (1982).

U. Giannini, Makromol. Chem. Suppl., 5, 216 (1981). Y. Doi, M. Murata, K. Yano, and T. Keii, 1st Eng. Chem. Prod. Res. Dev.,

580 (1982).

J.C.W. Chien and C. Kuo, J. Polym. Sci., Polym. Sci. Ed., 23, 761 (1985) W.F. Brockmeier and J.B. Rogan, Ind. Eng. Chem. Res. Dev., 24, 278 (1985

P.J.T. Tait and S . Wang, Brit. Polym. J., g, 499 (1988). W.R. Schmeal, J.R. Street, and J. Aiche, 17, 1188 (1971). D. Singh and R.P. Merrill, Macromolecules, 40, 599 (1971). Y. Doi, M . Murata, and K. Yano, Ind. Eng. Prod. Res. Dev., Y, 580 (1982). K.Y. Choi and W.H. Ray., J. Appl. Polym. Sci., 30, 1065 (1985).

P.J.T. Tait and N.D. Watkins, in "Comprehensive Polymer Science", ed., Sir G.

Allen, Pergamon Press, Oxford, 1989, Vol 4, p 533.

D.R. Burfield, I.D. McKenzie, and P.J.T. Tait, Polymer, 11, 302 (1972). I.D. McKenzie, P.J.T. Tait and D.R. Burfield, Polymer, 2, 307 (1972). V.A. Zakharov, G.D. Bukatov, N.B. Chumaevskii and Yu. I. Yermakov, Makromol.

Chem., 178, 967 (1977). L.L. Bohm, Polymer, 19, 553 (1978). U. Busico, P. Corradini, A. Ferraro and A. Proto, Makromol. Chem., 187, 1125 (1986).

N. Kashiwa, J. Yoshitake and T.Tsutsui, in "Transition Metals and

Organometallics as Catalysts for Olefin Polymerization", ed., W. Kaminsky and

H. Sinn, Springer-Verlag, Berlin, 1988, p 33.

P.J.T. Tait and N.D:Watkins (to be published).

P.J.T. Tait, in "Preparation and Properties of Stereoregular Polymers", ed.,

R.W. Lenz and F. Ciardelli, D. Reidel Publ. Co., Dordrecht, 1980, p 85.

A.D. Caunt, S . Davies and P.J.T. Tait, in "Transition Metal Catalyzed

Polymerizations", ed., R.P. Quirk et al., Cambridge University Press,

Cambridge, 1988, p 105.

V.A. Zakharov, G.D. Bukatov, N.B. Chumaevskii, and Yu. I. Ennakov, React.

Kinet. Catal. Lett., 1, 247 (1974). P.J.T. Tait, B.L. Booth and M.O. Jejelowo, Makromol. Chem., Rapid Comn., 2, 393 (1988).


29

3. Gas Phase Polymerization of Propene with MgCh Supported Catalyst

A. GUYOT’) , R. SPIT2 ’ ) , C. BOBICHON” and J.L. LACOMBE 2 ’

1) CNRS - Laboratoire des Materiaux Organiques BP 24 - 69390 VERNAISON (France)

2) DPFG ATOCHEM - Mont - BP 3 ARGAGNON - 64300 ORTHEZ (France)

ABSTRACT

Gas phase polymerizations were achieved in a stirred reactor with the catalytic system comprising a magnesium chloride, dibutylphtalate and titane tetrachloride solid and a trialkylaluminium (AA) phenyltriethoxysilane cocatalytic mixture. In realistic conditions (60-80’ C and 8-20 bar total pressure) activities and selectivities are in the ranges of suspension polymerization (up to 7000 g polypropylene per g catalyst in 1 hour with 97 0 isotactic index). The chain lengths are controlled by a very small hydrogen pressure (< 0.3 bar) so that an effect of hydrogen consumption on the productivity and molecular weight is observed. Hydrogen improves the activity. The reaction is very sensitive to hydrogen pressure, to the choice of the AA, to the AA/silane ratio and also to long polymerization times. The reaction rate is proportional to propene pressure with and without hydrogen.

INTRODUCTION

simplify the polymerization process as much as possible. More precisely, handling of solvents is to be avoided so that the traditional suspension process for Ziegler-Natta polymerization is to be replaced by processes involving the monomer and the catalyst only. In the case of propene polymerization, two processes are then possible: the liquid pool process in which the monomer is the suspension medium, and the gas phase process.

Natta, i.e. TiCl,-AlR,Cl, is now to be replaced by the more active catalytic system supported on Mgcl,, including a solid precatalyst with the support, TiC1, and a so-called internal Lewis base (ILB), and a cocatalytic solution with AlR,and an external Lewis base (ELB). Two main families of these supported catalytic systems are to be considered, according to the nature of the Lewis bases. In the most studied family, the two Lewis bases are aromatic esters l ) ; in a more recent, but more efficient family, the ILB is an aromatic diester,

The modern trends in industrial polymerization of olefins is to

On the other hand, the traditional catalytic system designed by

30 A. Guyot, R. Spitz, C. Bobichon and J. L. Lacombe

while the ELB is a silane compound '). The purpose of this paper is to describe and discuss how these

two families of catalytic systems behave in the conditions of a gas phase process.

PXPBBINENTAL A spherical reactor (1.45 1) with a stirrer scraping the reactor

wall at a short distance (0.5 mm) was used, under argon atmosphere. A cocatalytic solution containing the silane (phenyltriethoxysilane PTES) and the alkylaluminium (0.5 ml of triethylaluminium TEA or trihexyaluminium THA) in heptane (1 mole/l) is prepared in a small flask (50 ml) under argon. After 5 min., a small charge of porous polypropylene, previously treated 1 hour under vacuum at 60' C, is added to the flask. After two minute stirring, the precatalyst, prepared as previously described 2 , is added to the flask. After homogeneisation, the catalytic system (precatalyst + charge) is transfered under argon into the reactor at room temperature with gentle stirring (100 rpm). Then H, is added, the temperature is raised to the polymerization temperature and the monomer added to the desired pressure and the stirring rate increased to 350 rpm. Throughout the polymerization, the pressure is maintained at the fixed value from a reservoir and the monomer consumption rate is followed with a propene calibrated mass-flow meter (Brooks model 5850 TR).

work, unless specified, are : monomer pressure : 8 bars : H, : 85 cm3 : alkylaluminium (TEA or THA): 0.5 mmole i silane : 0.05 mmole. The temperature is 70' C and polymerization is stopped after 90 min.

The polymer is characterized by its melt index MI, under 2.16 Kg at 190' C and its isotacticity index H I (percent insoluble in boiling heptane : Kumagawa extraction for 2 hours).

The standard conditions for polymerization used throughout this

RESULTS AND DISCUSSIO# A first set of egperiments was carried out using the first family

of supported catalysts, including aromatic esters as an ILB (ethylbenzoate) and ELB (ethylbenzoate or methylphtalate). The activities are often rather high but the heptane insoluble fraction never approaches 90 b in the temperature range considered : 65-75. C. Higher values were reported at lower temperature ' ) , but the trialkylaluminium-aromatic ester system is not thermally stable enough and is decomposed under polymerization conditions ' ) . In the gas-phase polymerization conditions, the stabilization of the complex by the monomer ' I is not very efficient, the concentration being always lower than in a slurry.

an ILB and PTES as an ELB, the results are much better. When using the second family of catalyst with dibutylphtalate as

3. Gas Phuse Polymerivltion of Propylene with MgC12 Supported Catalysts 31

Table 1. Comparison of suspension and gas phase polymerization : productivities, isotactic index and melt index. Polymerization conditions : 70' C ; 90 min. : cocatalyst : triethylaluminium and phenyltriethoxysilane

Productivity IH MI, g. polym. /g. cat ( I )

Process Monomer pressure H, (bars)

cm3 bars

suspension 4 0 0 1270 97.5 0.3

Suspension 4 48 0.1 1190 97.6 3.2

Gas phase 8 0 0 1780 97 0.2

Gas phase 8 87 0.08 2240 97.2 5.7

Upon cgmparison between suspension (monomer pressure 4 bars) and gas phase polymerization (Table l), it is clear that, both in the absence or in the presence of hydrogen, the selectivity of polymerization versus isotactic placement remains excellent in the gas phase process. Owing to the different monomer pressure and concentration, the productivities are different. Without H,, the molecular weights are similar. In the presence of H2, some differences are observed, due to a higher amount of H, used. However, the H, consumption is lower (about 30 I instead of 50 I), so that the deactivation of the catalyst is slower. This fact is illustrated by fig. 1 and 2 in which typical curves are shown for each process either in the absence (fig. 1) or in the presence of H,.

It is interesting to note, in the absence of H, that, despite the fact that the nominal monomer concentrations are not the same, the rates are very similar in the two processes. The question is then raised of what is the actual polymerization medium. The catalytic system is initially dispersed in a polymer charge : under monomer pressure and at 70' C, a part of the monomer is expected to be dissolved in the amorphous phase of the growing polymer. This viscous medium is supposed to be the actual medium of polymerization containing also the cocatalytic solution.

The kinetics are strongly dependent on the nature of the alkylaluminium. As shown in Fig. 3, using THA instead of TEA, a net maximum in the rate is observed. The behavior is again similar to the case of suspension polymerization, although more pronounced : the activation of the active sites most probably requires a reduction process of the titanium, as suggested by Chien ' ), and the reducing power of THA is lower than that of TEA.

32 A. Guyot, R. Spitz. C. Bobichon and J. L. Lacombe

.C

500- CC lu L

c

- I I I I I

Figure 1. Gas phase and heptane suspension polymerizations. Kinetics without hydrogen. The polymerization conditions are : 70' C ; cocatalyst : TEA ; TEA/PTES = 10 ; total pressure : suspension : 4 bars ; gas phase : 8 bars. The polymerization rate is expressed in g polymer per g catalyst p hour.

( 0 - ) gas phase ; (A---- ) slurry

I I I I I 3 0 6 0 90

TIME ( m i n )

Figure 2. Gas phase and heptane suspension polymerization with hydrogen. Conditions : see figure 1 Hydrogen pressure : slurry 0.1 bar ; gas phase : 0.08 bar

( * ----- ) gas phase : (+ - ) slurry

3. G a s Phase Polymerization of Propylene with M&12 Supported Catalysts 33

Table 2. Influence of the nature and amount of alkylaluminium - standard gas phase polymerization conditions

Alkylaluminium Amount Al/Si P IH MI2 (mmole) g/g . cat. ($1

- - TEA 0.2 10 0

TEA 0.5 10 2280 96.3 5.70

TEA 2 10 2350 96.5 12.0

THA 0.5 10 1400 96 5.85

THA 1 15 1700 92 10.7

THA 2 20 2000 90 6.6

The effect of the Al/Si ratio was studied using THA. The data, reported in Table 2, show that both the productivity and the selectivity are dependent on that ratio, somewhat more than it was observed in suspension polymerization with TEA. Increasing the alkylaluminium amount causes the molecular weight to decrease, with either THA or TEA. The anomalous result obtained with a high THA/Si ratio might be due to an artefact in the rheological measurement, owing to the rather high amount of atactic material, i.e. demixing of low molecular weights in the melt ' ). A minimum TEA amount is necessary to activate the catalyst, but above that minimum, the TEA concentration has no large effect, except upon molecular weight.

It has been checked that, as mostly admitted, the reaction rate is proportional to the monomer pressure, at least in the low range of pressure. Increasing the pressure, the productivity increased near the amount obtained in liquid pool (30 bars) at the same temperature (table 3).

If compared to the 4-8 bar range, the activity at 20 bars seems too low, taking into account that more hydrogen is used. In fact the production of polymer in the experiment is so high (200 g) that the activity is certainly underestimated, the hydrogen consumption during polymerization can be estimated to about 30 0 of the hydrogen present ' ) . The use of THA may also account for the lower activity.

70' C. Kinetic curves in the 60-80' C range are shown in fig. 4. The activity increases with polymerization temperature, up to


id 0 3 000-

000-

000-

I I I 1 1 I I I I I 1

30 6 0 9 0 1 2 0

TIME (min)

Figure 3. Gas phase polymerization with triethylaluminium and trihexylaluminium Standard polymerization conditions with 0.08 bar hydrogen

(* ----) TEA ; ( 0 - ) m

Figure 4. Standard polymerization conditions with 0.08 bar hydrogen

Gas phase polymerization at different temperatures.

(* - ) 60' C ; (0 ----) : 70' C ; (A --*-) : 80' C

3. Gas Phase Polymerization of Aopylerce with M&12 Supported Catalysts 35

Table 3. Influence of the monomer pressure

Productivity HI MI, g/g . cat. (2)

Pressure HZ cm'

(bars)

4b ) 85 2240 97.2 5.7

6b ) 85 3420 - 2.2

8b ) 85 4250 97 1.4

20' ) 175 6800 97 0 . 9

30' ) 2 bars 10000 96 4.2

30' 3 bars 13000 96 11.4

a) THA : 60 min. : b) TEA ; c) liquid pool ; 60 min. ; TEA.

Table 4 . Influence of the temperature

Temperature Productivity HI MI, g/g.cat. ( 0 )

60 1680 95 4 . 8

70 2280 97.5 5.7

80 2240 96 7.8

Above 70' C, although the initial activity is higher, the productivity (Table 4) does not change very much, because the stability of the catalytic system begins to decrease faster. The selectivity remains high up to 80' C, while the molecular weight tends to decrease upon increasing temperature, as expected.

The tacticity may decrease if the polymerization duration is long.


Table 5. Effect of the duration of polymerization

Cocatalyst Duration Amount of Productivity HI M I 2 (min.) polymer (9) g/g.cat. ( 0 )

THA 60 55 1400 96.8 5.85

THA 120 80 2000 95.5 2.15

TEA 60 65 2240 97.5 5.70

TEA 180 120 3700 92 2.90

As shown in Table 5, the effect is moderate using THA, but more important using TEA. The kinetic curves (fig. 3) show that the activity decreases more using TEA than using THA. This effect may be due to the higher reducing power of TEA. However, since the reaction medium is the swollen polymer, upon increasing the polymerization duration, there is a dilution effect, which may partly explain the increase in molecular weight (the actual concentration of alkylaluminium decreases) : there is also possibly a higher consumption of hydrogen, acting as a transfer agent. The effect of dilution on the tacticity might be also due to some "extraction" of the very stable complex between alkylaluminium and silane from the catalyst surface, where it may be a part of the bimetallic isospecific sites : it was explained elsewhere e.) that the tacticity is governed by the equilibrium between this complex adsorbed onto the solid catalyst or dissolved in the medium : such equilibrium is of course slightly dependent on the concentrations.

co#cLuBIoI

those experienced in suspension : namely, the actual concentration of alkylaluminium in the actual reaction medium (amorphous polymer swollen by the monomer) is much higher. Very stable catalytic systems are then needed. It is not the case for the systems including aromatic monoester as Lewis bases : it is the case with the more recent family of supported catalysts including silanes as the ELB. Then, the behavior of these catalysts in a gas phase process and in either a suspension process or a liquid pool process should be very similar.

The conditions of a gas phase process are much more severe than

ACXNOHLBWEIIENTB

help. The authors thank ATOCHEM, groupe Elf-Aquitaine for support and

3. Gas Phase Polymerisation of Propvlene with MgCl, Supported Catalysts 37

REBERBNCEB 1. P.C. Barbe, G. Cecchin, L. Noristi, Adv. Polym. Sci., a, 3(1987) 2. R. Spitz, C. Bobichon and A. Guyot, Makromol. Chem., W, 707

3. Y. Doi, M. Murata, K . Yano, T. K e i , Ind. Eng. Chem. Proc. Res.

4. R. Spitz, J.L. Lacombe, M. Primet, J. Polym. Sci. Polym. Chem. Ed. ,

5. J.C.W. Chien, S. Weber, Y. Hu, J. Polym. Sci., Polym. Chem., 22,

6. P. Masson, R. Spitz, J. Appl. Polym. Sci., 34, 1335 (1987) 7. R. Spitz, P. Masson, C. Bobichon and A. Guyot, Makromol. Chem.,

8. R. Spitz, C. Bobichon, M.F. Llauro, A. Guyot, L. Duranel, J. Mol.

(1989)

Dev., 21, 580 (1982)

22, 2611 (1984)

1499 (1989)

m, 717 (1989) Cat. ( i n press)


39

4. Ethylene Polymerization in Gas - Phase and Slurry Reactors

M. 0. JEJELOWO, N. BU, D. T. LYNCH and S. E. WANKE

Department of Chemical Engineering, University of Alberta Edmonton, Alberta, Canada T6G 2G6

ABSTRACT

A comparative study has been made of ethylene polymerization in gas-phase and

slurry reactors using a b-TiCI3 and two high-activity catalysts prepared by impregnating

chemically-modified silica with T i c 4 . The results for the 6-TiC13 catalyst showed that

normalized activities based on ethylene concentration in the solvent for the slurry reac-

tor and gas-phase ethylene concentrations for the gas-phase reactor were independent of

solvent and reactor type. The high-activity catalysts had different rate versus time pro-

files which were a function of the catalyst preparation, the type of the co-catalyst and

the conditions of polymerization. For systems exhibiting decay-type profiles, it was found

that the rate of deactivation was much larger in the gas-phase than in the slurry reactor.

The data for the high-activity catalysts also suggest that catalyst activities obtained with

slurry reactors cannot be related directly to gas-phase activities. In the slurry reactor, no

significant variation in catalyst activity was observed when different solvents were used as

long as the activities were based on the concentration of ethylene in the solvent and not

on the partial pressure of ethylene above the solvent.

INTRODUCTION

Slurry reactors, rather than gas-phase reactors, are used in the majority of labora-

tory studies of catalytic olefin polymerization. Results from slurry reactors are frequently

used to predict the activity of catalysts for gas-phase reactors. Gas-phase processes are

40 M. 0. Jejelowo, N. Bu, D. T. Lynch and S. E.Wanke

increasingly being used for commercial production of polyolefins since gas-phase operation

has significant advantages over slurry and solution processes'#'.

Semi-batch slurry reactors are most commonly used in laboratory studies because

they are much easier to operate than semi-batch gas-phase polymerization reactors. The

two main operational problems for gas-phase reactors are proper suspension of the solid

particles (stirring) and temperature control. Heat transfer from the catalytically active

sites in the "core" of the growing polymer particle is dependent on how effectively the

surrounding gas phase, which is a very poor heat transfer agent, can remove heat to the

reactor heat exchange surfaces3. As a result, the temperature of the growing polymer

particles can be much higher than that measured by temperature probes in the reactor.

These high temperatures can result in rapid catalyst deactivation, possibly by physical en-

capsulation of the catalyst by 'molten' polymer. Reproducible introduction of the catalyst

and co-catalyst into gas-phase reactors is another problem. However, these problems can

be largely alleviated by proper design of the gas-phase reactor, and by using appropriate

operating procedures and conditions. In the present study, the catalytic activities of three

catalysts were determined using a slurry reactor with various solvents and a gas-phase

reactor. The objective of the study was to determine whether catalytic activities obtained

with a slurry reactor could be related directly to those obtained from a gas-phase reactor.

EXPERIMENTAL

Materials

Anhydrous magnesium chloride (1.5% HtO) and titanium tetrachloride (99.9%)

were obtained from Aldrich. Alkylmagnesium compounds were obtained from LITHCO

(in hexane) and from Texas Alkyls (in heptane). Samples of silica were obtained from

W. R. Grace (290 mz/g) and Gom PQ Corporation (330 m'/g), and they were pretreated

up to 6OO0C, where necessary, under NS before use. Solvents were distilled fresh from

CaHn or from K-benzophenone complex (THF), and were stored over sodium wire where

4. Kinetics of Ethykne Polymerization irp Gas-Phase and Slutvy Renciors 41

desirable and sampled under N2. Aluminum alkyls were obtained from Texas Alkyls and

were used either in pure form or in hexane solution. Ethylene (CP grade) and nitrogen

(99.999%) were obtained from Linde and prior to use they were passed through individual

purification trains for the removal of oxygen, moisture and carbon dioxide.

Catalysts

Three catalysts were used in the present study and these catalysts were always

stored and sampled under nitrogen in a VAC glove box containing <2 ppm oxygen and

<5 ppm water. The first catalyst was a commercial CTiCls Stauffer AA Type 2.1 cata-

lyst. The other two catalysts were silica-supported high-activity catalysts prepared in our

laboratory according to published procedures. The two laboratory-prepared catalysts are

designated as SMST and SMHNT.

The SMST catalyst was prepared by a method similar to that described in the

patent literature'. The procedure we used consisted of the following steps: suspending

10 g of silica in 70 cmS of n-heptane; adding 0.01 mol of Mg(n-C4Ho)2 in hexane; stirring

the suspension at room temperature for 3 h; adding 50 cms of Sic,; stirring at room

temperature for 60 h; increasing the temperature to 80°C; stirring at 80°C for 5 h; filtering

the solution; washing the solid four times with 100 cms of heptane; treating the solid with a

large excess of Tic14 at 80°C; removing the excess Tic4 by washing six times with 100 cm3

of heptane; and finally drying the solid at 60°C in uacuo. This procedure resulted in the

SMST catalyst containing 3.9 wt% Ti.

The SMHNT catalyst was prepared using a procedure similar to the one described

by Spitz et al.'. The procedure we used consisted of the following steps: 4.2 cm3 of a

saturated aqueous solution of MgCl2 was added to hexane containing 10 g of suspended

silica; the mixture was stirred at room temperature for 15 h and dried at 110°C in uacuo;

the dried solid was mixed with 2 g of NH'Cl and the mixture heated to 600°C in flowing


nitrogen. The resultant solid was treated with T i c 4 by the same procedure as for the

SMST catalyst. The SMHNT catalyst had a Ti content of 3.4 wt%.

Reactors

Two semi-batch reactors were used in this study. The slurry reactor was a 0.5-liter

jacketed glass reactor. The slurry reactor was operated at atmospheric pressure. The

gas-phase reactor was a ontliter stainless steel reactor which was immersed in an oil bath

for temperature control. The solids in the gas-reactor were kept in suspension by an AE

MagneDrive stirrer.

Gas flow rates were monitored by Matheson mass flow transducers and pressures

were controlled by pressure regulators. Flow rates, temperatures and reactor pressure were

recorded at 10 s intervals by a data acquisition system interfaced with a Hewlett Packard

1000 mini-computer. Details regarding the reactor system will be presented elsewhere".

RESULTS AND DISCUSSION

Overall rates of polyethylene formation are directly related to the feed rate of ethy-

lene to a semi-batch reactor operated at constant pressure and temperature. However, to

compare the activity of various catalysts it is necessary to normalize the rates with respect

to monomer and catalyst concentrations. This normalization is usually done by means of

a simple rate expression which is first order in monomer and catalyst concentrations', i.e.

where R,, = rate of polymerization, gp,/(g of cat-s)

&p = rate constant, gp,/(mol Ti-s-[mol C,H,/mS])

[MI = monomer concentration, mol C,H4/mS

[Cat] = Ti concentration in catalyst, mol Ti/g of cat

4. Kinetics of Ethylene Polymetization in Gas-Phase and Slum Rmtors 43

Hence, Ic, values are activities which are normalized with respect to monomer and catalyst

concentrations, and these kp values can be used to compare activities for different catalysts

or for the same catalyst in different reactors or at different monomer concentrations. If the

intrinsic rate of polymerization is first order with respect to monomer concentration, as

assumed in Equation 1, and if mass and energy transfer effects are negligible, then the kp,

for fixed co-catalyst concentration and constant temperature will be independent of the

monomer concentration and reactor type. However, the correct value of the concentration

has to be used for calculation of kp.

For gas-phase reactors, the monomer concentration to be used in Equation 1 is

unambiguous, i .e. it is equal to the gas-phase concentration. For most of the conditions

encountered in catalytic gas-phase ethylene polymerization, the gas-phase concentration

of ethylene, Go is adequately approximated by the ideal gas law, i.e.

For slurry reactors, the concentration of monomer in the solvent should be used for

calculation of kp. This, however,. has not been the usual practice in the literature. Usually

polymerization rates are normalized with respect to the total pressure or the monomer

partial pressure in the head-space of the slurry reactor. The total pressure can differ

significantly from the monomer pressure if the solvent vapor pressure is appreciable at the

operating temperature. Use of the monomer partial pressure is somewhat better since the

concentration of monomer in the solvent is directly proportional to the monomer partial

pressure in the pressure range where Henry’s law is applicable. However, comparisons of

activities in slurry reactors based on the partial pressure of the monomer above the solvent

are only valid for a single solvent since the solubility of the monomer is a function of the

solvent.

In the current study, the activities, i.c. k,, values, obtained in the gas-phase reactor


are compared with activitiee obtained in the slurry reactor. Activities for the slurry reactor

wil l be based on the vapor-phase concentration of ethylene in the head-space, Csv, and

the concentration of ethylene in the solvent, C S L . The concentrations of ethylene in the

solvents were estimated using the Peng-Robinson equation of state'.

Results obtained with the Stauffer AA, Type 2.1 catalyst are summarized in Table 1.

Previous investigations in our laboratory have shown that the intrinsic rate of gas-phase

ethylene homo-polymerization over the StaufEer AA, Type 2.1 catalyst is essentially first

order with respect to ethylene concentration; hence, the kp values should be constant since

mass and energy transfer processes were probably not significant. Examination of the

relative activities in Table 1 shows that the values for the slurry reactor based on CSL and

the value for the gas-phase reactor are essentially the same, i.c. the kp value is independent

of solvent and independent of reactor type. If comparison of activities had been based on

Csv, then the erroneous conclusions that the catalyst's activity in the slurry was two to

three times higher than the activity in the gas-phase reactor and that the activity in n-

heptane is 50% higher than the activity in n-decane would have been made. These results

clearly demonstrate that comparison of catalytic activities for slurry reactors should be

based on the concentration of monomer in the liquid phase and not on the partial pressure

of the monomer above the solvent.

Comparison of activities in slurry and gas-phase reactors for the SMST catalyst is

presented in Figure 1; the dashed lines are activities in the slurry reactor based on the

concentration of ethylene in the vapor phase, i.c. Cm, while the solid lines adjacent to

thesolvent designations are based on the ethylene concentrations in the respective solvent,

i.e. CSL. Four general observations can be made from the results presented in Figure 1;

one, all the activities are time dependent; two, the activity in the gas phase is significantly

lower than the activities in the various solvents; three, activities in the solvents which are

based on Csv (dashed lines) are solvent dependent; and four, activities for the solvents

4. Kinetics of Ethylene Polymwiurrion in &-Phase and Sluny Renctms 45

Table 1. Ethylene polymerization activity in slurry and gas-phase reactors. [Stauffer AA Type 2.1; DEAC; 70°C; Ethylene pressure in gas-phase reactor - 0.3 to 0.4 MPa].

REACTOR SOLVENT ACTIVITY, g,,/(mol Ti-s-[mol C A / m S ] ) Based on csv C S L C G

Slurry n-heptane

Gas-Phase - n-decane

- 0.291 0.121 0.208 0.124 - - - 0.111

CSV concentration of ethylene in vapor-phase of slurry reactor CSL concentration of ethylene in solvent in slurry reactor CG concentration of ethylene in gas-phase reactor

based on CSL are essentially solvent independent.

The observation that the normalized activities based on CSL are not dependent on

the solvent reinforces the previous conclusion that CSL rather than CSV should be used

for comparing activities. The normalized activities for decalin are somewhat lower than

those for heptane and decane. The probable cause of this difference is the inaccuracy of

the ethylene concentration in decalin predicted by the Peng-Robinson equation of state.

The time dependence of the activities seen in Figure 1 is due to catalyst deactivation.

It is apparent that deactivation of the SMST catalyst in the presence of triethyl aluminum

(TEAL) is more rapid in the gas phase than in the solvents. The difference in deactivation

rates between gas and solvent operations could result from various causes such as differences

in the rates and degree of Ti+' reduction caused by differences in TEAL concentration on

the surface of the catalyst, differences in the temperature of catalyst particles due to

heat transfer limitation in the gas phase, and differences in the inhibition by products

of the reduction processes. The causes of the differences in deactivation rates were not

46 M. 0. Jejelowo. N. Bu, D. T. Lynch and S. E.Wanke

investigated, but the large differences in deactivation rates for the SMST/TEAL system

make direct comparison of rates from the slurry reactor with those from the gas-phase

reactor impossible. Constant activities would make direct comparisons much easier.

Relatively constant activities were obtained with the SMST catalyst by using iso-

prenylaluminum (IPRAL) as the co-catalyst. The activity profiles for the SMST catalyst

with IPRAL and TEAL as co-catalysts are shown in Figure 2 for gas-phase operation.

The rapid deactivation obtained with TEAL is probably due to over-reduction of the Ti+4

since IPRAL has much less reducing power than TEAL. IPRAL is a 3-dimensional poly-

meric formed from the reaction of isoprene with tri-isobutylaluminum. The

compound is believed to contain isobutyl and 2-methyltetramethylene groups and gives

upon hydrolysis isobutane and 2-methylbutane". The exact structure of IPRAL is not

well defined, and the mechanism involved in stabilizing and increasing the activity of the

SMST catalyst is not known, but the IPRAL may stabilize the catalyst in a manner similar

to that described for the oligomeric aluminoxane in soluble Ziegler-Natta systemP.

The effects of TEAL and IPRAL on the general behavior of the SMHNT catalyst,

which are shown in Figure 3, are similar to those found with the SMST catalyst. The

deactivation of the SMHNT catalyst in the gas-phase reactor was even more severe than the

deactivation for the SMST catalyst (c j . Gas-Phase/TEAL lines in Figures 2 and 3). The

gas-phase activity profiles, on the other hand, for the SMHNT/IPRAL and SMST/IPRAL

are very similar in shape, even the normalized activity values are very similar (e.g. about

1.1 g,,/(mol Ti-s-[mol C2H4/ma]) for both catalysts after 60 min on stream). However,

the shape of the activity profile for the gas-phase SMHNT/IPRAL system and the slurry

SMHNT/IPRAL system are quite different (see Figure 3). The activity for the slurry

reactor, based on CSL in Figure 3, increased at a lower rate than the activity for the gas-

phase reactor during the initial stages, but the activity of the slurry system increased for

a longer period so that after 120 min on stream the activity in the slurry was about 1.5

4. Kinetics of Ethylene Polymetizutkm in Gas-Phuse and Sluvy Reucfors 47

times as large as the activity in the gas phase.

The variations in the rate of change of activity with respect to time M well as the

magnitude of the activity is not only a function of the catalyst and the type of co-catalyst,

but also depends on the amount of co-catalyst ( i .e . the A1 to Ti ratio). The role of

the co-catalyst includes among other things, reducing the transition-metal atom thereby

creating a coordinatively unsaturated entity which is the basis for monomer coordination,

insertion and chain propagation. There is, however, a limit to how far the transition-

metal should be reduced without losing catalyst activity and, the necessary reduction level

is often revealed by determining the rate of polymerization as a function of the molar ratio

of the aluminum alkyl to the transition-metal. Figure 4 shows the relationship between

the amount of co-catalyst (TEAL and IPRAL) and activity for the SMHNT catalyst in

the slurry reactor. Two data point for gas-phase operation are included for comparison.

The relatively low activity for the gas phase for the SMHNT/IPRAL system may be due

to the low vapor pressure of IPRAL which could result in a low concentration of IPRAL

on the surface of the catalyst during gas-phase operation. Additional experiments with

varying amounts of IPRAL in the gas-phase reactor are needed to verify this conclusion.

Figure 4 also illustrates that the activity variation with A1:Ti ratio is very depen-

dent on the type of co-catalyst. In the slurry reactor for the SMHNT/TEAL system, a

maximum in activity was obtained for a A1:Ti molar ratio in the 40 to 60 range. No such

maximum was observed for the SMHNT/IPRAL system; for this system the activity in-

creased up to an A1:Ti ratio of about 60 and thereafter remained relatively constant up to a

ratio of 135. In addition, the maximum activity for IPRAL was about twice the maximum

activity obtained with TEAL. Relatively constant catalytic activities are desirable during

investigations into the effects of operating conditions on reaction rates and for studying

rates of co-monomer incorporation. The use of IPRAL, or similar co-catalysts, will thus

facilitate the interpretation of results of such studies with high-activity catalysts.

48 M. 0. Jejelowo. N. Bu, D. T. Lynch and S. E.Wanke

CONCLUSIONS

The preliminary results on the polymerization of ethylene have clearly shown that

the concentrations of ethylene in the solvent (Cst), and not the partial pressure or concen-

tration of ethylene above the solvent (Csv), should be used when activities are compared

for different solvents or with activities determined in a gas-phase reactor. It has also been

shown that high-activity catalysts of the type used in this study when used in conjunction

with TEAL deactivate much more rapidly in gas-phase reactors than in slurry reactors.

The high-activity catalysts did not deactivate when IPRAL was used as a co-catalyst, but

the normalized activities in the gas-phase reactor were lower than those in the liquid-phase

reactor. The shapes of the activity-time profiles were also different, i.e. the activation

rates were not the same for the gas and slurry systems.

Direct comparison of normalized activities was possible for gas and slurry reactors

for the &Tic18 catalyst since the activity of this catalyst was essentially constant. How-

ever, the differences in activation and deactivation rates observed for the high activity

catalysts in gas-phase and slurry reactors makes direct comparisons of activities obtained

with these two types of reactors impossible. Quantitative understanding of the differences

in activation and deactivation processes in the two types of reactors or the development of

operational procedures which eliminate these differences is required before direct compar-

ison of rate data for slurry and gas-phase reactors is possible.

Acknowlufgmcnk - The support of this research by Novacor Chemicals Ltd. and the

Natural Sciences and Engineering Research Council of Canada is gratefully acknowledged.

4. Kinetics of Ethylene Polpwht ion in Gas-Phase and SIuny Reactors 49

REFERENCES

1. Karol, F. J., in "History of Polyolefins" (R. B. Seymour and T. Cheng, Eds.), pp. 193-211, D. Reidel Publ. Co., Dordrecht, 1986.

2. Short, J. N., in "Transition Metal Catalyzed Polymerization - Alkenes and Dienes, Part B" (R. P. Quirk, Ed.), pp. 651-669, Harwood Academic Publ., New York, 1983.

3. Floyd, S., Mann, G. E., and b y , W. H., in "Catalytic Poiymerization of Olefins" (T. Keii and K. Soga, Eds.), Studies in Surface Science and Catalysis, Vol. 25, pp. 339-367, Elsevier, Amsterdam, 1986.

4. Caunt, A. D., Gavens, P. D., and McMeeking, J., European Patents 0 032 308 and 0 032 309 (1981).

5. Spitz, R., Pasquet, V., and Guyot, A., in "Transition Metals and Organometallics as Catalystsfor Olefin Polymerization", (W. Kaminsky and H. Sinn, Eds.), pp. 405-416, Springer-Verlag, Berlin, 1988.

6. Lynch, D. T., and Wanke, S. E., Can. J. Chem. Eng. (submitted for publication).

7. Tait, P. J. T., in "Transition Metal catalyzed Polymerization - Alkenes and Dienes, Part A" (R. P. Quirk, Ed.), pp. 115-147, Harwood Academic Publ., New York, 1983.

8. Peng, D.-Y., and Robinson, D. B., Ind. Eng. Chem., Fundam., 16,59-64 (1976).

9. Mole, T., and Jeffery, E. A., "Organometallic Compounds" p. 74, Elsevier, Amster- dam, 1972.

10. Guyot, A., Spitz, R., Duranel, L., and Lacombe, J. L., in "Catalytic Polymerization of Olefins" (T. Keii and K. Soga, Eds.), Studies in Surface Science and Catalysis, Vol. 25, pp. 147-162, Elsevier, Amsterdam, 1986.

11. Lehmkuhl, H., and Schiifer, R., Leibigs Ann. Chem., 706, 23-31 (1967).

12. Kaminsky, W., in "Transition Metal Catalyzed Polymerization - Alkenes and Dienes, Part A" (R. P. Quirk, Ed.), pp. 225-244, Harwood Academic Publ., New York, 1983.


n n rn

E \ d,

ho

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Time, minutes Figure 1. Ethylene polymerization activity in gas-phase and slurry reactors.

[SMST catalyst; TEAL m-catalyst; 60OC; P , , = 0.1 MPa (slurry) or 0.5 MPa (gas-phase)].

4. Kinetics of Ethylene Polyme?izariorC in Gas-Phase and Sluny Reactm 51

1.4

1.2

1.0

0.8

0.6

0.4 o.21 0.0

0 30 60 90 120

Time, minutes Figure 2. Effect of type of co-catalyst on polymeriration rate behavior.

[SMST catalyst; TEAL co-catalyst, 8OoC, PCaR,=o.!% MPa; IPRAL co-catalyst, 90°C, Pc2a,=O.06 MPa].


1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0 0 30 60 90 120

Time, minutes Figure 3. Ethylene polymerization activity in gas-phase and slurry reactors.

[SMHNT catalyst; gas-phase, 90°C, PCJR,=o.4 MPa;

slurry phase, 70"C, PcJR,=O.l MPa].

4. Kinetics of'Ethylene Polymniurtwn in Gas-Phase and Slum Reoctm 53

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

-

-

-

.

-

-

0 30 60 90 120 150

A1 : Ti molar ratio Figure 4. Effect of co-catalyst concentration. [SMHNT catalyst; 70°C]


55

5. Differences in Kinetic Parameters of Various Kinds of MgC12- Supported High Yield Catalysts

MINORU TERANO* , TAKUO KATAOKA* , TOMINAGA KEII** *Toho Titanium Co., Ltd., Japan

152 , Japan

3-3-5 Chigasaki, Chigasaki-shi, 253,

* * Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo

ABSTRACT

observe a quasi-living polymerization state of propene. It was found that molecular weight distribution remained constant from the very beginning (0.1 s ) of the polymerization. Kinetic parameters were dependent on the catalyst preparation methods.

A new method called stopped-flow polymerization was used to

INTRODUCTION Many types of high yield catalysts have been proposed and

studied both in academic and industrial lab~ratories.l-~) differ in efficiency, tacticity and kinetic behavior according to their different preparation methods and starting materials used.

It is known that the average molecular weight of a polymer produced by polymerization with traditional Ziegler catalysts based on TiC13 increases gradually with time to reach a stationary value. The dependence of number-average molecular weight, Mn, on polymerization time, t, has been expressed by the Natta equation14)

They

-

[c*l + ktr[c*1t with Y = kp[M1[C*lt (2) where Y, Mo, [MI, [C*l, kp, and ktr are polymer yield, molecular weight of monomer, monomer concentration, concentration of polymerization centers, and the rate constants of propagation and transfer, respectively. Using these relations, we can evaluate values of kp, ktr as well as [C 1. MgC12-supported TiC14/ethylbenzoate(EB) catalyst a transitional change of average molecular weight has not yet been recognized clearly, even in the beginning of the polymerization up to 5 s ,

* In the case of a highly active

56 M. Terano, T. Kataoka and T. Keii

because of rapid transfer since ktr > > 0.2 s-l5).

of Eqs. (1) and (2), observation of the transitional change of molecular weight in a quasi-living polymerization state, where the transfer reaction is negligibly small, is needed.

polymerization. A quasi-living polymerization state (0.1 - 1.0 s ) of propene polymerization with typical MgC12-supported high yield catalysts was observed in order to discuss the effect of the catalyst preparation method on some kinetic parameters by using the above method.

In order to precisely evaluate the values of kp, etc. by means

Here, we apply a new method called stopped-flow

EXPERIMENTAL Three types of catalysts prepared by various procedures were

used in this study: cat-A: 30 g of MgC12 with 11 m2 surface area and 15.4 g of

TiC14-EB complex were placed in a 1 1 stainless steel vibration mill pot with 50 balls under nitrogen and ground for 30 h at r.t. The obtained product was further washed with heptane.

cat-B: 30 g of MgC12 with 11 m2/g surface area and 6.5 cm3 of EB were placed in the vibration mill pot under nitrogen and ground for 30 h at r.t. 6.1 g of the coground product was treated with 200 ml of TiC14 in a 500 ml flask at 9O'C for 2 h with stirring under nitrogen, then washed with heptane.

cat-S: 5.0 g of MgC12 with 11 m2/g surface area was dissolved in 25 cm3 of 2-ethylhexylalcohol with 2.5 cm3 of EB at 130'C under nitrogen followed by dropwise addition into 200 cm3 of TiC14 at - 2O'C with stirring. The suspension obtained was gradually heated up to 9O'C and maintained at the temperature for 2 h followed by washing with heptane.

cat-S was spherical.

is shown in Figure 1.

concentration [MI and temperature of the polymerization mixture in the Teflon tube, (a) to (b), the polymerization conditions were adjusted to hold monomer conversions below 10%. Polymer obtained was washed with plenty of ethanol and dried in a vacuum. Average molecular weight and molecular weight distribution were measured using Waters GPC-150.

The shape of cat-A as well as cat-B was irregular and that of

The stopped-flow polymerization apparatus used in this study

In order to avoid a significant change in monomer

5. Kinetic Parameters in Some M&lZ Supported Catalysts Ziegler-Natta Cutalpis 57

Figure 1. A simple stopped-flow polymerization apparatus. (A):Catalyst suspension in heptane; (C):Ethanol: (D):Teflon tube: (a):A simple three-necked joint.

(B):Al(CzH5)3/heptane solution;


20'C are illustrated in Figure 2. The polymer yield, Y, is proportional to t, and the reverse values of the degrees of polymerization, lfin and l/Fw, are linear versus l/t. Then E q s . (1) and (2) can be applied with a constant concentration of polymerization centers, [C*], and the following relation holds for 1/Fn :

The results obtained for the polymerization using cat-B at

58 M. Terano, T. Kataoka and T. Keii

A

15

5

0

0.0 5.0 10.0

l l t (s ' l )

Figure 2. Experimental results obtained for cat-B at 20 C. Propylene pressure = 1 bar, [MI = 0.72 mol/l, [A1(C2H5)3] = 70 mmol/l and [Ti] = 2.3 mmol. Plots against l/t: ( A ):l/Y,(@ ):l/h, ( V 1 : 1/Pw and ( ) :fiw/h. ( A , 0 , v , 0 ) :Data obtained using a conventional polymerization technique (reaction time: 10 s).

5. Kinetic Parameters in Some M&l, Suppotled Catalysts Ziegler-Natta Catalysis 59

From the against l/t we Combining this S

P tangent and the intercept of the plot of l/F obtain kp = 1230 l-mol-'.s-' and ktr = 1 s- . value of k with the value of Y/t(= 2500 g.mo1-Ti-' P

- l ) f which was re-expressed per unit concentration of [Ti] from the observed value at [Ti1 = 2.3 mmol/l, we obtain [C*1 = 0.06 mol/l or [C*]/[Ti] = 6 mol-%. These results appear plausible. The value of ktr supports the foregoing result that no transitional change in molecular weight was recognized for the polymerization at 40" C in the range of 5 s to 3 h.5) energy of ktrf this value would be larger at 40'C. two results obtained here should be noted: First, the initiation reaction (polymerization center formation) is so rapid that it is completed within 0.1 s; second, the polydispersity, Mw/M,, is constant from the very beginning of the polymerization, as shown in Figure 2. The rather large value of polydispersity remains constant even at this stage of polymerization without significant transfer reaction, which proves that both the change in transfer reaction7) with chain length and the existence of thick polymer layers8) leading to diffusion limitation cannot explain the broadening of molecular weight distribution: only the non- uniformity of active centers can, as proposed by one of the present authors (T.K.') ) on another basis.

Three types of typical MgC12-supported catalysts were used for the stopped flow polymerization of propene to investigate the effect of catalyst preparation method on some kinetic parameters. Results obtained are summarized in Table 1.

Because of the high activation In addition,

Table. 1 Kinetic constants at 30'C determined for a series of catalysts prepared by different methods.

cat. -A 2.5 2250 2.0 0.17 80

cat. -B 2.1 2180 2.4 6.0 3110

cat. - S 5.0 4750 5.0 0.48 480

60 M. Terano. T. Kataoka and T. Keii

It is seen that the kinetic constants vary depending on the catalyst preparation method. The values for k are similar between cat-A and cat-B, whereas cat-S shows more than twice the values for the other two catalysts. But the reason why cat-S exhibits higher value for kp as well as k respect to the value of [C I , both cat-A and cat-S had lower than 1 % but only cat-B showed as high as 6%. From the process by which the catalysts are prepared, it may be that Ti species contained in cat-B are supported on the surface of a catalyst particle and that cat-A and cat-S, which are prepared by grinding method and dissolution-precipitation method, provide the Ti species not only on the surface of catalysts but also inside the catalyst particles. From the viewpoint of catalyst preparation method, we suppose that the differences in the kinetic parameters are due to the difference of supporting place in the Ti species. That is, Ti species in cat-B may be supported on the surface of catalyst particle, while those in cat-A and cat-S may exist all over the particle as illustrated in Figure 3 . Therefore, the values of [C*l for cat-A and cat-S are quite low at the very primary stage of polymerization as the amount of Ti species on the surface may be very small in these two types of catalyst.

P

is not clear at this moment. With t&

Q . * *

cat-B c a t 4

Figure 3 . Schematic drawing of a series of catalysts showing difference in supporting place of Ti species.

5. Kinetic Parameters in Some MgCl, Supported Catalysts Ziegkr-Natta Catalysis fil

From these results, it is understood that different catalysts with different kinetic parameters can be produced by different preparation methods even if the same starting materials are used.

ACKNOWLEDGEMENT

technical contribution to this work. The authors are grateful to Mr. Takeyasu Maruyama for his

REFERENCES 1 W. Kaminsky et al.(eds), Transition Metals and Organometallics

as Catalysts for Olefin Polymerization(l988), Springer-Verlag, Berlin, Heidelberg.

2 Jap. 432533 (1964), Shell invs.: W. A. Hewett, E. C. Shokal 3 Jap. 1014471 (1981), Mitsui Petrochemical, invs.: A. Toyota, N.

4 G. Natta and I. Pasquon, Adv. Catal. 11 (1959) 1. 5 E. Suzuki, M. Tamura, Y. Doi and T. Keii, Makromol. Chem. 180

6 Japan Kokai 56-811 (1981), Mitsui Ptrochemical invs.: M. Kioka,

7 M. Gordon and R. J. Roe, Polymer 2 (1961) 41. 8 D. Singh and R. P. Merill, Makromolecules 4, (1971)'599. 9 T. Keii, Y. Doi, E. Suzuki, M. Tamura, M. Murata and K.

Kashiwa.

(1979) 2235.

K. Kitani and N. Kashiwa.

Soga, Makromol. Chem. 185 (1984) 1537.


63

6. Kinetic Profile of Polymerization with Cr-Oxide/SiOa Catalyst

ARILD FOLLESTAD, STEIN HELLEBORG, VIDAR AIMQUIST

Statoil, 3960 Stathelle, Norway

ABSTRACT

Polymerization with Cr-oxide/Si02 catalyst gives initially low

activity, then a gradual increase in activity.

Several factors are discussed that might be responsible for the

long time to reach full activity: Chemical, transport

restrictions, catalyst fracturing.

A locking and unlocking of Cr-C bond cycle is proposed.

A concequence of this theory is that as soon as the pores in the

catalyst have been filled with polymer, polymerization must

virtually stop. Slowly, however, pressure in the pores build up

and fractures the catalyst, making an increase in polymerization

rate possible.

INTRODUCTION

It is the aim of this study to give additional insight in some aspects of the kinetics of high-yield slurry polymerization with

Cr-oxide/silica catalyst. This catalyst system is extensively

used in industry.

The kinetic profile of polymerization has been described by

various authors (1,2,8,9,10,12,13,17).

64 A. Follestad, S. Helleborg and V. Almquist

Using a Cr03/SiOz catalyst in semibatch slurry high-yield

polymerization experiment, one sees (fig. 1, curve a):

- A period of very slow polymerization rate for 5-60

minutes (below measurable range).

- An acceleration rate period for more than 20

minutes.

Tim Imln.1

FIG. 1. A c t i v i t y vs. time in high yleld semi-

batch slurry polymerization in isclbutane a t 104OC a n d 38 bar total pressure.

a) - 1% Cr on Grace 952 silica , (210 A mean poredlameler).

air activated at 680' C.

b) ---- As a) and afterwards CO reduced at 350' C

c) -..-. As b) and ,044 g TEAlg catalyst added before ethylene

The very slow polymerization rate can be accounted for by slow

reduction of hexavalent chromium or by slow removal of oxygenated

compounds made during reduction of Cr, away from active site

regions (l,lO,ll).

The active site is often considered to be Cr2+ ( 7 , 8 ) .

By using prereduced catalyst (Cr2+) one can eliminate the very

slow rate period (fig. 1, curve b). But also for this catalyst,

the acceleration rate period persists with activity starting

close to zero.

6. Kinetic Profile of Polymerkation with Cr-oS&lSi02 Catalyst 65

B. Rebenstorf (3) Yield -0,3 glg [ Gas phase

As the primary purpose of this paper is to discuss the kinetics

of the acceleration period, for sake of simplicity a prereduced

(Cr2+) catalyst is considered hereafter.

2 t 0,5% Cr 0,06%C?'

The first question we have asked is:

CHEMICAL OR PHYSICAL EXPLANATION OF RATE ACCELERATION

It has been thought that the rate acceleration is caused by

generation of new active sites during this period: A chemical

explanation (15,16). It has also been speculated that a physical

factor such as catalyst fragmentation could be rate limiting.

It is useful to compare results of polymerization under mild and

tough conditions.

Table 1. Active site determinations.

I CATALYST

6 t 1% Cr

0,05% Cr6+

P. Hogan (15)

TIME MIN. -

>I5 -60 -60

- 10 - 10

TEMP OC

>I00 >I00 >I00

20 80

METHOD

Poisoning Concentr. effect Concentr. effect

Polymer chains Polymer chains

ACTIVE SITES IN % OF Cr

16 8 40

15 65

Lowered concentration of Cr is known to give higher proportion of

active sites (15). The Rebenstorf and the Hogan results fall

well on line.

These results strongly indicate that the Cr2+/silica catalyst

under extremely mild conditions, rather fast can give the same

number of active sites as under much more industrial-like

conditions.


We have considered to explain the fast initiation of active sites

in low yield gas phase polymerization by a very high rate of

diffusion of poisons out of the catalyst. Under slurry process

conditions, diffusion coefficient is at least three orders of

magnitude lower than for low yield gas phase polymerization. The

slow initial polymerization in slurry experiments could perhaps

be explained by the slower removal of poisons.

We do not favor this explanation however, because we do not think

enough poison is generated by a reaction between a prereduced

catalyst and ethylene to give this large effect.

The other possible explanation considered, which we favor, is

that the very initial polymerization rate also in slurry

polymerization really is very high, but that it has extremely

short duration. For low yield gas phase polymerization, the high

activity lasts only until a yield of about 0,3 g/g is reached.

This is approximately

yield polymerization experiment and would therefore not be

detected there.

of the total yield in a slurry high-

Our conclusion is that the prereduced catalyst soon after

bringing ethylene and catalyst together, chemically has a high

activity. But there is some kind of physical limitation at work that depresses the rate to the low value that is observed

initially in high-yield slurry polymerization.

We will go on to look at suspected physical factors.

MONOMER MACROPARTICLE DIFFUSION RESISTANCE

The term macroparticle diffusion resistance is used as defined by

Ray and coworkers (3) in their multigrain model. If there is a

very significant resistance, this could be the physical factor

limiting rate. At an early stage when polymer particles are

small the polymerization rate would be much reduced, later

polymerization rate would increase.

6. Kinetic Profile of Polymerization with Cr-oSidelSiOz Catalysf 67

As shown by McDaniel (1) experimentally by using catalysts of

different particle size, this is not the case (except perhaps

during the extreme initial polymerization period). Furthermore

other types of silica-supported PE catalysts (Ziegler type) even

show very high activity during the first minutes of

polymerization under similar process conditions.

Therefore we conclude that macroparticle diffusion resistance can

not be the physical factor limiting rate during the acceleration

rate period.

FRAGWENTATION BACKGROUND

In order to discuss other physical factors, it is necessary to

first discuss what happens to the catalyst particle.During

polymerization, the original catalyst particle breaks up into

fragments incorporated in the polymer particle.

Fig. 2 Scanning electron micrograph of polymer particles at mean yield 108 g/g in slurry polymerization with Grace 952 silica as carrier. Left side: Polymer particle. Right side: Detail of polymer particle

showing lamellar surf ace.

a. Polymer particle b. Detail of polymer particle showing lamellar surface

Fig. 2 shows a polymer particle at low yield. It may be imagined

that the growing process is a laborious process.


It can be seen on fig. 3 that the original catalyst particles are

fragmented during polymerization.

fragment sizes is observed at this low yield, ranging from 0 , l

micron (fig 3b) to the few fragments from an original 50 micron

particle still preserving their original relative positions

(fig. 3a).

A mixture of different

Fig. 3. Scanning electron micrograph of catalyst fragments after ashing of polymer particles with mean yield 29 g/g in slurry polymerization, with Grace 952 silica as carrier. Initial catalyst size - 50 micron.

a. Large fragments showing resemblance of an initial catalyst particle.

b. Small fragments

Conner et al. (5) found fragmentation already at the extreme low

yields of around 2 g polymer/g catalyst. This yield is

approximately the same as what is needed to fill the catalyst

pores. McDaniel (1,4) suggests the fragments to be 0.1-1 micron,

or at least less than 7 micron early in the polymerization

period. Tait (22) has found a fragment size at high yield of

0.06 micron. Kakugo et al. (6) have measured the size of Tic13 Ziegler catalyst fragments and found these to be of the order of

0,Ol micron.

6. Kinetic Profile of P o l ~ t i t m with Cr-CkidelSiO, Catalyst 69

The fragmentation takes place because the polymer produced in the

catalyst pores generates a pressure inside the catalyst particle

thereby exploding it. At the end of the acceleration period,

polymer generated within a fragment flows to the outer surface of

the fragment with a pressure drop less than the critical pressure

to rupture the fragment.

THE POLYMER TRANSPORT PROBLEM

The polymer in the pores is mainly a solid material. The volume

within the outer surface of a fragment then consist of two

continous, intermixed networks of solid material: Polymer and

silica'. (See fig. 4 ) . Neither of these two networks can flow

relative to the other without rupturing one of the networks.

I I1

Fig. 4. Unit cell of a simple structure of two intermixed continous phases.

I: Both phases together. 1 1 and Ill: Each of the two phases by itself.

Only by disrupting the silica or by overcoming the critical

(rupture) shear stress for the polymer can the polymer be able

flow through the silica network. We estimate that this critical

shear stress is about 1-5 bar at these conditions. This means

that if the flow paths are long compared to pore diameter, the

total pressure drop caused by the flow will be unreallistically

high.

to

70 A. Follestad. S. Helleborg and V. Almquist

It follows that:

- Fragments with a radius similar to pore size can

produce polymer at high rates all through the

fragments. Since a typical pore diameter is 200 A, it

follows that this happens for fragment diameter less

than 0.05-0.1 micron.

- Larger fragments only produce significant amounts of

polymer in the outer shell since elsewhere there is no

way for the polymer to get out.

From the abovementioned description it follows that down to 0 , l

micron particle size an approximate rate equation can be written:

where: Q is rate of polymerization, A is fragment outer surface,

kA rate constant based on fragment outer surface area and p

monomer pressure at fragment outer surface.

A reasonable maximum ultimate fragment size for an active

catalyst in high yield polymerization, we consider is about 0,l

micron. This is based on the results by Tait mentioned earlier.

Supporting this is that higher values would mean that the

catalyst is designed such that only a small fraction of the

fragment volume can be active for fast polymerization.

Furthermore the fraction of active sites of total Cr determined

by poisoning should be expected to give very low values if only a

small fraction of fragments volume is active for fast

polymerization.

DOES NON-FRAGMENTATION HINDER POLYMERIZATION?

The question is whether this factor hinders polymerization rate

significantly in practice, or whether polymerization proceeds at

the same rate unhampered by having to explode the catalyst

structure or by fragment size.

6 . Kinetic Profile of Polynrerisation with Cr-Oxide/Si02 Chtalyst 71

For reasonable activity in high-yield slurry polymerization, a

mean pore diameter of more than 100 A is needed (1). A mean pore

diameter of 200 A would be typical for this catalyst.

The 60 A pore diameter catalyst used by Rebenstorf in the earlier

mentioned experiments should therefore not be active in high-

yield slurry polymerization. But its activity in low yield gas

phase polymerization was almost comparable to the activity of a

good catalyst tested in high-yield slurry polymerization. This

activity lasted until a yield of approximately 0,3 g/g was

reached.

Groenefeld et al. (20) polymerized ethylene using a catalyst

support of only 24 A average pore diameter. It was found that

polymerization was initiated at many more sites than actually

was making polymer macromolecules.

This shows that at the very start, these low diameter catalysts

are active, but polymerization rate decreases soon.

By analogy, we believe there is a similar effect for the higher

pore diameter catalysts. But here the rate decrease effect is not

so detrimental.

We conclude that unsatisfactory fragmentation is the limiting

factor for the rate in the acceleration period.

HOW DOES NON-FRAGMENTATION HINDER POLYHERIZATION?

We have considered several explanations for non-fragmentation

hindering polymerization.

Total Dressure effects on euuilibria with tr ansition state or

monomer dissolved in amOrDhOUS D olvmer.

There is a possibility that the total pressure in the pores

becomes so high that it seriously affects an equilibrium that may

be important for the rate:


- Either between reactants and transition state for the

propagation step.

- Or between monomer in the liquid phase and in polymer

in the catalyst pores.

We have tried to estimate critical pressure needed to explode a

catalyst particle. We believe the main critical pressure range is

within the region 2-20 bar. This estimate is based on the pure

silica rupture strength of about 500 bar and a typical porosity

of 8 0 % , as well as on the implosive force of liquid water in the

pores during the silica drying operation.

The rate reduction effects can be calculated by the influence of

the pressure on the Gibbs free energy of the equilibria. The

calculations show that even though there may be some effects of

this factor if the overpressure in the pores varies as much as

100 bar, it certainly cannot explain rate variations of a factor

as high as 2.

MicroDarticle monomer diffusion resistance.

This is a factor that could be limiting polymerization rate.

Following the terminology of Ray and coworkers (3) again we

consider the polymer microparticle surrounding one catalyst

fragment . A large fragment will exhaust its vicinity of monomer. The local

concentration of monomer in that fragment will be low.

On the other hand, a small fragment will have almost the same

high monomer concentration as the greater part of the polymer

particle.

If then fragments break gradually during the course of

polymerization, the monomer concentration in the fragments will

be gradually increased, and there would be a rate increase.

6. Kinetic Rofik of Polymeriurtion with Cr-OxidelSi02 Catalyst 73

When polymerizing under different partial pressures of ethylene

we have observed roughly an inverse proportionality between

ethylene concentration and melt index. (The melt index is a

measure of molecular weight). Also polymerization rate is

proportional to ethylene concentration.

According to this explanation, it should be expected that during

the course of a polymerization: The monomer concentration in the fragments should be proportional to activity and the melt index

inversely proportional to activity. Actually, melt index

decreases with increasing yield (fig. 5) as should be expected,

supporting this explanation.

Actlvlty

Yield (g/g)

FIG. 5. Activity and MI vs yield in high yield semibatch slurry polymerization.

Calculated melt index for polymer Meaaured melt index. chains made at Qiven moment.

Activity (g,,g.min,br,) - ---- ---

Another observation that also support this explanation is the

effect of increasing the amount of Cr on the catalyst support.

This gives higher activity based on total catalyst and therefore

should be expected to reduce ethylene concentration in the

fragments and thereby increase melt index. Melt index is indeed

observed to increase.

74 A. Follestad, S . Helleborg and V. Almquist

For low activity runs caused by catalyst poisons the ethylene

concentration of the fragment (equal size) should be expected to

be high and therefore melt index to be low. Actually, it does not

seem that catalyst poisons influence the yield - melt index curve of fig. 4. So the effect of catalyst poisons does not support

this explanation.

There is also the possibility to calculate the effect of

diffusion resistance directly.

Looking first at a fragment larger than 0,l micron where eq. 1

can be used, the effectiveness factor (ratio of rate with, versus

without monomer diffusion resistance) is:

2. E=-- 1 + -A

2P

where: d is fragment diameter and P is permeability of monomer in

polymer.

Also assuming that at the end of the polymerization, all

fragments have the reasonable diameter of 0,l micron and low

diffusion resistance, the area based activity has a value of

3 * 10'' g/(s, cm2, bar) for the catalysts of fig. 1.

Based on results by Michaels and Bixler (14) a value of

permeability of 5 10 -lo g/(cm, s, bar) for ethylene in

polyethylene can be estimated at 1OO'C. However, this is a far

temperature extrapolation of their experimental data and neither

takes into the account differences in thermal history nor

solvating effect of isobutane on amorphous polymer. We take the

abovementioned value to be a minimum value.

The effectiveness factor according to eq. 2 is seen on fig. 6. It

is seen that the assumption of low diffusion resistance at 0,l

micron was valid. Further is seen that a large degree of

diffusion limitation exists only for unreasonably large fragments

or for unreasonably low permeability values.

6 . Kinetic Profile o f P o l ~ t i O n with Cr-C?ri&lSi02 Catalyst 75

0.01 I

1.0

0.8

0.6

0.4

0.2

FIG. 6. Efficiency factor versus fragment size and permeability. - 0 -9 2

P=5.+ld P=5.*10 P=S.+# _-.--. g/(s,cm ,bar) - - - - -

---- ---.._ ---..- -- 4.

By a similar calculation it can be shown also that fragments less

than 0,l micron are far from having a monomer diffusion

resistance.

We therefore discard the hypothesis that monomer diffusion

resistance is in any way responsible for the acceleration rate

period.

Slow Dolwnerization in the framen t cores.

It was shown earlier that fragments larger than approximately 0,l

micron has a central core where no or extremely slow

polymerization takes place. Therefore if fragment size is

reduced during polymerization, polymerization rate will increase,

according to eq.1.

This explanation is supported by the results of P.J. Tait

mentioned earlier. His ultimate fragment size of 0.06 micron is

at the lower limit of where we consider reduction in fragment

size gives increased activity. We favor this explanation. We will

go on to show the mechanisms by which this can happen.


THE WCKING PROCESS THAT STOPS POLYMERIZATION IN THE FXAGMENT CORES

Initiation of active sites we believe takes place through a

period of many seconds. During this time polymer is made from the

already initiated sites. The pores of the catalyst get filled

with polymer. During these seconds this polymer, being below the

melting/solution temperature, has time to assume some kind of

partly crystalline form within the catalyst pores. This should be

possible because the mean diameter of a catalyst pore is about

200 A while the initial lamella thickness of the polymer is about

100 A (18,19).

The regularity and fraction of crystalline material within the

catalyst pores will probably be lower than outside giving a

different enthalpy (less stable) than outside. But the entropy of

the amorphous polymer phase constricted within the pores is also

lower than outside. The melting/solution temperature of the

polymer within the pores could then still be the same as outside

of the pores.

The polymerization will stop as the neighboring polymer segments

to an active site are locked between crystalline regions and pore

walls. Then the necessary movements in order to insert another

monomer can no longer happen.

In addition, also in amorphous regions the polymer segments tend

to get into an increasingly stable structure with time, making

less and less segment movement possible.

We conclude that this locking of Cr-C bonds must be the process

responsible for stopping polymerization in the cores of fragments

larger than 0.1 micron.

6. Kinetic Profile of Polymehtion with Cr-oXidelSi02 Catalyst 77

WHICH PROCESS CAUSES THE DELAYED F'RAGXENTATION?

According to eq. 1, in order to explain the gradual rate

increase, a sradual fragmentation process is needed. It is

however, not evident that the proposed locking of Cr-C-bonds

should give a gradual fragmentation.

Only the silica phase of a polymer filled catalyst particle is

responsible for keeping the high-modulus silica network structure

together. The polymer phase cannot keep silica network structure

together.

Silica at polymerization temperature is a brittle material with

low elongation at break and equal rupture strength regardless of

a period of 1 second or 1 hour stress.

Even for this high-surface silica, it seems highly improbable

that rearrangement of silica atoms takes place caused by stress

or by the energy release of monomers being snapped into the

chains at active sites.

Therefore one could have expected that as soon as pores have been

filled, either the mechanical strength of the catalyst is so high

that no fragmentation can happen, or so low (for a more porous,

high pore diameter catalyst) that instantaneously complete

fragmentation takes place.

We have examined two explanations for the delayed fragmentation.

The first is based on the fact that wide pores or holes in the

catalyst takes much longer time to fill because of low

surface/volume ratio. Also these wide pores should represent weak

zones of the catalyst where it should be most easy to fracture.

So with a wide distribution of pore size, a wide distribution of

catalyst structure fracturing time is expected. But using the

known pore size distribution, it can be calculated that almost

all pores are filled early in the acceleration period. So this

explanation must be discarded for our present problem.


The second explanation is based on the pressure increase rate

within the pores. The just-produced, partially crystalline

polymer within the pores will certainly have difficulty in

achieving an even pressure distribution on the pore wall at the

moment the pore is filled. There may be high pressure associated

with the active site, and in some parts where crystalline regions

touches pore walls (fig. 7a). Elsewhere there would mostly be the

low pressure associated with deforming the amorphous phase

polymer from its thermodynamically most stable (ball-like) form.

Fig.7 Schematic illustration of the initial polymerization in a catalyst pore.

Polymer chains shown. Length of arrows indicate relative polymer pressure. 100 A: H

a. Pore just filled: Polymer segments locking against further monomer insertion.

With increasing time, there must

b. Later, after some cycles of polymer stress relaxation and subsequent monomer insertion.

be a redistribution of polymer

segments in order to get pressure more even. This gives unlocking

of Cr-C-bonds and the opportunity for new monomers to be inserted

at an active site until the active site is again locked, and the

situation is back where it began except the pressure has

increased. Going many times through this time-consuming

locking/unlocking process, the polymer pressure in the pores will

reach a high value which is rather constant over a distance of a

pore diameter (fig.7 b). Eventually the critical pressure of the

catalyst structure is reached, and catalyst structure ruptures.

6. Kinetic Profik of Polmn.zatiOn with Cr-OxidelSiO, Catalyst 79

Owing to the inhomogenity of the catalyst structure which gives

both a distribution of critical pressure as well as a

distribution of pressure rate increase, there is gradual

fracturing, resulting in increasing polymerization rate. Our

conclusion is that this is the most probable delay factor.

A conctduence of this explanation is that fragments have a high-

pressure region core where virtually no polymer production takes

place, see fig. 8 . They have a low-pressure shell with fast

polymerization and where polymer flows out. Only the high-

pressure regions are responsible for catalyst ruptures.

Fig. 8 Schematic illustration of cross section of a catalyst fragment.

. . . . . . . . . . Low pressure shell with fast, unhindered propagation.

High pressure core with very slow, hindered propagation.

..

a. Before rupture b. After rupture

There is probably also a region in between these two regions

where propagation is hindered, but polymer escapes very slowly

into the low-pressure shell. The fraction of this region is

probably small since it should have some tendency to unstability:

Either propagation is so slow that the polymer segments reaches a

more stable condition making propagation still slower and flow

resistance still higher etc., at last completely stopping polymer

flow. On the other hand, if propagation is a bit faster, then

polymer segments does not have time to reach a stable condition,

making propagation still faster and flow resistance still lower

etc., at last making unhindered polymerization.


The fragmentation process can not go beyond the fragment size

where little or no high-pressure regions are left, which means

that fragments should not be much less than 0,l micron. In the

practical region of fragment size, activity should be roughly

proportional to fragment outer surface area, equivalent to

inversely proportional to fragment diameter.

RELEVANCE TO THE CrG+/SILICA CATALYST SYSTEM

We go on to discuss the relevance of our conclusions on the

Cr2+/silica system for the Cr6+/silica catalyst system.

With hexavalent chromium some factor, for instance reduction time

or diffusion time of catalyst poisons out from the catalyst

pores, gives an initial period of very low rate.

According to B. Rebenstorf (21), catalysts with chromium in the

hexavalent state are inactive for low yield gas phase

polymerization below 200'C. For the low yield gas phase

conditions, the diffusion rate of poisons cannot be limiting

polymerization rate. Under these conditions the absence of

activity must be caused by chemical factors, probably extremely

low rate of reduction of chromium. Going back to the high yield

slurry conditions (with 30 times higher monomer pressure) it is

probable that the same chemical factor is a main factor for the

initial very low rate period.

If the removal of poisons is also a rate-limiting process, the

rate of this should be enhanced by fragmentation, giving positive

feedback to further fragmentation.

When the acceleration rate period finally begins it is probable

that the effect of the abovementioned factor does not disappear

immediately, but disappears gradually.

We conclude that the acceleration rate period for the Cr6+/silica

system is determined by a combination of the gradual

disappearance of the factor responsible for the very low rate,

and the mechanism we are proposing for the Cr2+/silica case.

6. Kinetic Pmfik of hlymerLation with Cr-&&/Si02 Catnlyst 81

THE -EFFECT OF METAL ALKYLS

Adding some metal alkyl to the catalyst before ethylene, gives a

high initial polymerization rate. This effect is shown on fig.

1, curve c.

We explain this by a very fast initiation of all active sites and

propagation as ethylene diffuses toward the center of the

catalyst particle. Within the short time needed to fill the pores

(few seconds), there is not time for any crystallization or

optimum segment orientation.

Without any crystallization the polymer chains neighboring the

active site are able to move. Propagation proceeds unhindered of

the high pressure achieved after the pore is filled. There is

an instantaneous catalyst rupture. There is no delayed

fracturing.

It could also be that under these conditions some overheating of

catalyst and large fragments takes place for some seconds,

further stabilizing amorphous polymer versus crystalline polymer

phase.

Using a low amount of metal alkyl, some parts of the catalyst is

unaffected by this treatment.

It is noted that metal alkyls give a higher degree of polvmer

w t i c l e fracturing than is ordinarily observed. This is consistent with the view that rupturing is partly a monomer-

diffusion controlled process, giving extremely inhomogenous

productivity in a catalyst/polymer particle during the first

seconds.

Catalysts with organic chromium compounds on silica also exhibit

high initial activity (4). The explanation for this should be

the same as for the metal alkyls case.


KELT INDEX DECREASE DURING P0L;YIIERIZATION

As mentioned, melt index decreases with increasing yield

(fig. 5).

This melt index decrease could be caused by chemical phenomena,

or it could be caused by physical phenomena.

We cannot prove either of these two to be correct, but we have

looked further at the following physical explanations:

1. Low ethylene pressure in the initial large fragments.

This at least is not a major effect, as earlier

calculated.

2 . Decreasing local temperatures at active sites during

polymerization. But calculations show the overheating

effect to be insignificant.

3 . A change during polymerization of outer surface of

fragments from broad to narrow pores. Catalysts with

broad pores are known to make high melt index polymer

(1). It is reasonable to assume that the rather broad

pore size distribution of the catalyst is not evenly

distributed, but that there are regions of broad and of

narrow pores.

If so, the broad pores will be exposed on fragments

earliest since the earliest ruptures would preferrably

pass through the weakest regions. Hence: Initially

baoad pores dominates giving a high melt index, then

gradually mean pore size and melt index are lowered.

This is the explanation that we favor.

6. Kinetic profile of P o l ~ a t i o n with Cr-OxidelSiO~ Gztalyst 83

CONCLUSION

We find it plausible that physical and not chemical phenomena

determine the activity during the acceleration rate period for

the Cr2+/silica system, and propose:

- Observing a single catalyst pore:

* When at the start of polymerization the pore

has been filled, polymerization almost stops

due to polymer segments locked near the

active sites hindering the necessary

rearrangements to insert new monomer.

Segments are locked because of partial

crystallization in the pores.

* Slow unlocking then occurs, giving slow

polymerization in the pore, giving slowly

increasing polymer pressure.

- Then observing a catalyst fragment:

* A fragment ruptures when the mean polymer

pressure within the pores reaches the

critical pressure for the silica network of

that fragment . * Unhindered (fast) polymerization takes place

in the exposed low pressure outer shell of

the fragment. This shell depth is comparable

to the pore diameter.

- Observing total polymerization reaction with increasing

time :

* The mean fragment size is gradually reduced.


* Polymerization rate increases proportional to fragment

- Using also a metal alkyl in the catalyst

system, initiation is so rapid that the

polymer in the pore has no time to

crystallize while filling the pore. Since

there is no locking effect, further pressure

build-up in pores and fragmentation is

instantaneous.

For the Cr6+/silica system the acceleration rate

period is determined by a combination of the same

mechanism as for the Cr2+/silica system and a gradual

disappearance of the factor responsible for the very

slow rate period.

outer surface.

-

We further propose that the observed melt index decrease during

polymerization is caused by a shifting of exposed fragment

surface from broad to also narrow pores.

Elements of the theory proposed may also be relevant to other

polymerization systems containing a solid catalyst component.

References:

1. M.P. McDaniel : Adv. in Catalysis 33, 47 (1985).

2. B. Rebenstorf : 2 . Anorg. Chem. 212, 103 (1984).

3. W.H. Ray, S. Floyd, G.E. Mann in: Catalytic Polymerization of olefins. T. Keii, K. Soga, Eds. Kodansha, Tokyo 1986.

4. M.P. McDaniel: J. Polym. Sci. Polym. Chem. Ed. u,

5. W.C. Conner, E.L. Weist, A.H. Ali, M. Chiovetta,

1967 (1981).

R.L. Laurence in: Transition Metals Catalyzed Polymerizations, Ed. R.P. Quirk., Cambridge University Press 1988, p. 417.

Transition Metals and Organometallics as Catalysts for Polymerization, Eds. W. Kaminsky, H. Sinn, Springer- Verlag, Berlin 1988, p. 433.

6. M. Kakugo, H. Sadatoshi, M. Yokoyama, K. Kojima in:

6 . Kinetic Profile of PolymeriurtMn with Cr-Oxi&/SiO, Catalyst 85

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

2 0 .

21.

22.

23.

H.L. Krauss, H. Stach: Inorg. Nucl. Chem. Lett. L 393, (1968).

R. Merryfield, M. KcDaniel, G. Parks: J. Catal. 77. 348, (1982).

R. Spitz, B. Florin, A. Guyot : Europ. Pol. J. u, 441, (1979) . T.J. Pullukat, R.E. Hoff, M. Shida : J. Pol. Sci. Polym. Chem. Ed. l&, 2857, (1980).

H.L. Baker, W.L. Carrick : J. org. Chem. 616. (1968) . L..T. Finogenova, V.A. Zakharov, A.A. Buniyat-Zade, G.D. Bukatov, T.K. Plaksunov: Vysokomol. Soyed. No. 2 404, (1980).

2. Tvaruzkova, B. Wichterlova : J. Chem. SOC., Faraday Trans. 1, 79, 1591, (1983).

A.S. Michaels, H.J. brxler : J. Pol. Sci. x, 413, (1961). J.P. Hogan : J. Polym. Sci. A-l &, 2637.

V.A. Zakharov, Y.I. Ermakov : J. Polym. Sci. A-1 2, 3129.

M.P. McDaniel, M.B. Welch : J. Catal. a, 98, (1983). P.J. Barham, A. Keller : J. Pol. Sci. B 22, 1029,

I.G. Voigt-Martin, G.M. Stack, A.J. Peacock, L. Mandelkern : J. Pol. Sci. B 22, 957, (1989).

C. Groenenfeld, P.P.M.M. Wittgen, H.P.M. Swinnen, A. Wernsen, G.C.A. Schuit : J. Cat. H;L, 346, (1983).

B. Rebenstorf: Personal communication.

(1989) .

P.J. Tait : Personal communication.

Y. I. Yermakov, B.N. Kuznetsov, V.A. Zakharov: Catalysis by supported complexes, Elsevier 1981.


a7

7. Effects of the Structure of External Alkoxy Silane Donor in High Activity Ziegler-Natta Catalyst on the Microstructure of Polypropylene

Mika Hiirkanen, Jukka V. SeppEUti and Taito VMniinen*

Helsinki University of Technology, Department of Chemical Engineering, Kemistintie 1, SF-02150 Espoo, Finland

* Neste Chemicals, P.O. Box 310, SF-06101 Porvoo, Finland

ABSTRACT

Correlations were sought between the structure of external alkoxy silane donors and the microstructure of the obtained polymer chain. Propylene was polymerized in liquid monomer with a heterogeneous high activity Ziegler- Natta catalyst. Fifteen different alkoxy silanes of structure hSi(OR)4_n, where n=1-3, R = Ph or alkyl and R = C1-3 alkyl, were used as external donors. Polymers were fractionated by boiling heptane extraction. Microstructures of the polymers were studied by means of 13C NMR.

The structure of the donor had a marked effect on the catalyst activity and isotacticity of the polymer. Nevertheless, all of the alkoxy silanes tested produced qualitatively similar changes in the microstructure of PP compared to PP polymerized without external donor: the size of the isotactic mmmm- pentad peak in the 13C NMR spectra vaned with the donor, but the sizes the non-isotactic pentad peaks were more or less constant relative to one another, except for the syndiotactic rrrr-pentad peak, which relative to the other non- isotactic pentad peaks was decreased slightly in unfractionated PP and increased in the boiling heptane soluble fraction. These results suggest that all external alkoxy silane donor have the same qualitative effect on active centers, but the effectiveness and selectivity of deactivation strongly depend on the donor structure.

88 M. Harkonen, J. V. Seppala and T. Vaananen

Electron donors play an important role in modern catalysts for propylene polymerization. Recent breakthroughs in polyolefin catalyst and process technology have largely come about through an increase in empirical understanding and use of Lewis bases in a right way. However, the functional mechanisms of the reactions are poorly known.

The addition of external donor to the cocatalyst solution increases the isotacticity of the polymer. At the same time the activity of the catalyst usually decreases. However, the production of isotactic polypropylene increases as long as the donor/aluminium alkyl molar ratio is kept small enough. Typically the following effects of external donors are mentioned:1-8)

- Selective poisoning of atactic active centers - Transformation of atactic centers to isotactic ones - Increase in the propagation rate constant of isotactic centers - Deactivation of isotactic centers when the concentration of external donor is

high enough

Alkoxy silanes are cited as external donors in a large number of recent patents for Ziegler-Natta catalyst systems.9) The advantages of these donors became known in the early 80'8.10) Before the silanes, other types of Lewis bases, like aromatic esters or bulky amines, were used as external donors.

Information about alkoxy silane donors of various structure is mostly to be found in the patent literature.9810) Though some effects of the most common external alkoxy silane donors on polymerization of propylene have recently been published,l~3~6~11-13) scientific studies on the relationship between structure and polymerization behavior are few. Soga et al.14) and Iiskolals) have recently reported some interesting results for propylene polymerization in heptane medium with various external alkoxy silane donors. Considerable dependence was found between the polymerization behavior and the structure of the alkoxy silane. In our previous publication8) we examined the effect of the structure of external alkoxy silane donors on catalyst activity and the isotacticity of the formed polymer. Effects on catalyst active centers were also discussed. Our results were broadly similar to those of Soga and Iiskola .

7. Structural Effect of A l k w SiIane in MgcI, Supported Catalyst 89

The polymer chain is a "fingerprint" of the catalyst active centers, 80 that study of microstructure of the polymer chain handily provides information about the structure of active centers in the catalyst and the effect of different additives on them. The microstructure of polypropylene is most easily studied in the methyl carbon region of 13C NMR spectra.16-18) With modem high field NMR instruments even heptad configurations of PP chain can be determined rather easily.17~18) Microstructures of polypropylene up to hexads can be examined in the methylene region of the spectra.1820)

1% NMR investigations of polypropylene produced with MgCl2-supported high yield Ti-catalysts with external dononW1-S) have widely been reported during the 1980'8, but studies on the effects of the external donors on the microstructure are few.6373)

Our main purpose in this work was to study the influence of the structure of alkoxy silanes as external donors in supported Ziegler-Natta Ti-catalyst on propylene polymerization behavior, on the microstructure of the polypropylene, and on the active centers of the catalyst.

EXPERIMENTAL

Polymerizations were performed in liquid propylene in a 1 dm3 b tch react r. To ensure reproducibility, polymerizations were done in exactly the same way, with donor selection and donor amount as the only variations. The donor and aluminum alkyl were allowed to react 8 min before the catalyst and the cocatalyst were combined. The AVTi mole ratio was 200 in all experiments. After addition of 0.3 bar hydrogen, liquid propylene was added. The cocatalyat and the catalyst were together 5 min before the monomer was introduced. The polymerization time was 45 min and the temperature 60 "C.

The catalyst was a typical modern supported Ziegler-Natta catalyst of type MgC1~PTiCl~/DIBP-AlEt~/ext.donor (DIBP=diisobutylphthalate). Titanium content of the catalyst was 2.6% b.w. The alkoxy silanes tested, with their abbreviations, are listed in Table 1. Aluminum alkyl was 10% b.w. triethylaluminum (TEA) in heptane from Schering AG. Propylene was grade 2.5 from Messer Griesheim.


Activity of the catalyst was calculated from the Mg content of the polymer and the catalyst. Mg content of the polymer was determined from the diluted ash with an atomic absorption spectrophotometer.

The polymer was fractionated by extracting it 6 h with boiling heptane in a Soxhlet-type apparatus. The intrinsic viscosity measurements were determined at 135 "C with decahydronaphtalene as solvent. Selected samples were analyzed by GPC.

The microstructures of the polymers were determined by 13C NMR spectroscopy, using a JEOL GX-400 spectrometer. Pentad peak assignments in the methyl carbon region of the spectra are according to Zambelli et al.16) Lorenzian lines were fitted to the peaks in the methyl region by using the NMRl program supplied by New Methods Research. The curve fitting was done in VAX 3500 workstation.

Table 1. Compounds used as external donors.

Alkoxy silane Code Deliverer

Dimethyldiethoxysilane Dimethyldiisopropenoxysilane

Diphenyldimethoxysilane Diphenylsilane Dodecyltriethoxysilane Isobutyltrimethoxysilane

Methyldimethoxysilane Methyldodecyldiethoxysilane

Methylphenyldiethoxysilane

Methyloctyldimethoxysilane Methyltriethoxysilane Methyltrimethoxysilane Methyltri-p-propoxysilane

Phenyltriethoxysilane Phenyltrimethoxysilane p-propyltrimethoxysilane

Triethylsilane Trimethylethoxysilane Trimethylmethoxy silane

~~ ~~

DMDES DMDIPS DPDMS DPS DTES IBTMS MDMS MDDES MPDES MODMS MTES MTMS MTPS PTES PTMS PRTMS TES TMES TMMS

Petrarch Petrarch Petrarch Petrarch Petrarch Hiils

Petrarch Petrarch Petrarch F luka Alfa F luka Petrarch Alfa Petrarch F luka Petrarch Alfa F luka

7. Structural Effect of Alkmy Sikane in M&i2 Supported Catahst 91

In general, addition of alkoxy silane donor to the cocatalyst solution increased the isotacticity of polypropylene (PP) while decreasing the overall activity of the catalyst. However, the effects on the effectiveness to achieve high isotacticity of the polymer with satisfactory activity of the catalyst varied markedly with the structure of the particular donor. The results of the polymerizations are summarized in Table 2.

The external alkoxy silane donors studied could roughly be divided into three groups on the basis of performance. The best donors produced highly isotactic polypropylene, in association with high activity of the catalyst. The second group produced high isotacticity but the activity was very low. The third group was characterized by high activity and low isotacticity. Figure 1 shows the effects of a donor from each category on activity and isotacticity, determined by boiling heptane extraction. More detailed information and discussion of the effects of donors on the polymerization behavior have been presented in our previous paper.8)

15 t

9 . 10 0 Y c .-

0 0.05 0.1 0.15 0.2 DonorflEA mole ratio

1 I I

0.05 0.1 0.15 0.2 Donor/TEA mole ratio

Fig. 1. Activities and isotacticities (by extraction) representing the three characteristic groups of external alkoxy silane donors in bulk polymerization.

0 Php(MeO)pSi, I 0 Me3(EtO)Si, A A Me(MeO)$, 0 no donor

Results of polymerizntions

nodonor - 13.1 75.0 1.91

DMDES5 DMDES 0.2 5.1 92.4 2.46 DMDESIO DMDES 0.1 9 2 86.7 I .98 DMDES20 DMDES 0.05 8.7 81.6 1.86

DMDIPSS DMDIPS 0.2 6.5 85.7 2.15 DMDIPSIO DMDIPS 0.1 4.5 83.0 329 DMDIPSU) DMDIPS 0.05 8.7 83.5 2.00

DPDMSS DPDMS 0.2 7.6 99J 2.55 DPDMSIO DPDMS 0.1 8.0 98.5 320 DPDMS20 DPDMS 0.05 11.4 89.1 2.15

DPSS DPS 0.2 10.8 74.0 1.94 DPSlO DPS 0.1 10.2 77.0 1.98 DPSZO DPS 0.05 8.7 80.1 1.77

DTES5 DTES 0.2 4.2 98.2 2.18 mESl0 DTES 0.1 6.1 95.9 2.00 D m 2 0 DTES 0.05 8.3 87.9 1.79

DTMSS IBTMS 0.2 5.2 99.2 2.97 IBTMSlO IB'IMS 0.1 10.2 97.4 2.27 m'IMsu) IBTMS 0.0s 10.8 91.7 2.20

MDDES5 MDDES 0.2 2.7 94.7 2.15 MDDESIO MDDES 0.1 5.8 86. I 1.58 MDDES20 MDDES 0.05 6.2 80.9 I .68

MDMS2 MDMS 0.5 1.9 2.38 MDMS3 MDMS 0.3 2.9 93.9 2.35 MDMSS MDMS 0.2 7.6 91.8 2.39 MDMSIO MDMS 0.1 8.0 83.6 2.06 MDMS20 MDMS 0.05 7.6 81.2 2.44

MODMS5 MODMS 0.2 5.6 96.1 226 MODMSIO MODMS 0.1 8.7 89.0 223 MODMSZO MODMS 0.05 8.3 82.1 2.00

~ ~~~ ~

MPDESS MPDES 0.2 4.6 982 1.84 MPDESIO MPDES 0.1 5.9 94.0 1.98 MPDES20 MPDES 0.05 8.5 82.1 I .w

MIESS MN 0.2 3.5 978 203 M N l O MN 0.1 6.3 94.5 234

87.0 218 m20 MTES

MTMSS m s 0 2 1.5 973 2.58 MIMslO M I M S 0.1 4.8 91.1 234 m s 2 0 m s 0.05 8.3 89.1 234

O M 9.6

%S 1.67 m s 5 MTPS MIPS10 MTPS 0.1 5.4 895 1.84 m m Mlps 0.05 7.5 799 264

0.2 3.8

PTESS PlEs 0.2 6.3 99.4 213 98.5 2.17 PTESIO m s 0.1 7.1 89.4 2.08 m 2 0 PTES 0.05 7.6

~

98.0 2.51 P I M S 5 PTMS PIMSlO PTMS 0.1 7.6 %. I 2.7 I

91.4 2.09 mzo m s 0.05 103

0.2 6.5

PRTMSS PRTMS 0.2 2.2 97.6 3.20

PRTMS20 PRTMS 0,05 5.9 913 2 s PRTMSlO PRTMS 0.1 4.7 953 2.n

TESS TES 0.2 10.8 78.1 I .74 TESlO TES 0.1 10.8 783 1.77 mu) TES 0.05 9,6 79.5 2.06

TMEsl TMEs 1.0 4.4 912 229 85.5 2.45 TMEs2.5 TMES 0.4 10.2

TMESS TMES 0.2 13.1 85.2 1.81 84.0 233 TMEslO TMEs 0.1 10.8

TMEs20 TMES 0.05 13.1 842 2.17 TMEs40 TMEs 0.025 10.2 78.0 2.00

TMMSS TMMS 0.2 11.4 82.9 2.44 TMMSIO TMMS 0.1 8.7 81.5 216

R I .4 1.80 TMMS2O TMMS 0.05 10.7

7. Structural Effect of A h y Sikrne in MgC12 Suppotfed Cutalyst 93

5 2 3 -

s 2 -

F

n LL v) v)

1 -

0

"he use of donor had a clear influence on the average molecular mass and the molecular mass distribution (MMD). As Figure 2 illustrates, relative to the polymer prepared in the absence of donor, the amount of short chain polypropylene was decreased and the amount of long chain polymer increased. Similar effects have been reported in some recent publications.1,6) Since the shift to higher molecular mass in the MMD was accompanied by a notable increase in isotacticity, the increase in the average molecular mass of the polymer was evidently due to a decrease in atactic polymer and an increase in high molecular mass isotactic polymer.

DPDMSKEA = 0,05

DPDMSKEA = 0,2 NO DONOR

I ,

Fig. 2. Effect of diphenyldimethoxysilane as external donor on MMD of unfractionated PP.

Effect of an external alkoxy silane donor on the methyl carbon region of the 13C NMR spectrum is shown in Figure 3. The changes in the microstructure of unfractionated PP as increasing amounts of a good external alkoxy silane donor were added are shown in a form of a block diagram in Figure 4. The isotactic mmmm peak can be seen to increase in the size and the non-isotactic pentad peaks to decrease as the donormA mole ratio inc&ases. Although the relative sizes of the non-isotactic pentad peaks are about the same in all spectra, the syndiotactic rrrr pentad peak is decreased relatively more than the other non-isotactic peaks.

94 M. Harkonen, J. V. Seppa'la and T. VPnanen

i v \ I1 I TEA = 0.1

Fig.3. Effect of external diphenyldimethoxysilane donor on methyl carbon region peaks of the 13C NMR spectrum of unfractionated PP.

Pentads

Fig. 4. Effect of the addition of a good external alkoxy silane donor on the microstructure of unfractionated PP.

7 . Stnatural Effed of Alkay Silane in MgClz Supported Catalyst 95

Figure 5 shows the changes in the spectrum of the boiling heptane soluble fraction for the same good donor. Again there are systematic changes with the increase in amount of donor. Here, however, the size of the syndiotactic rrrr pentad peak is clearly increased as well as that of the isotactic mmmm pentad. Also, some increase in the mmrr pentad is observed. The relative amount of all other, more or less atactic, structures in the polymer chain is decreased when the amount of donor is increased. The fact that the influence of small amount of donor is more emphasized in the boiling heptane soluble fraction than in the unfractionated polymer (see Fig. 4) suggests that the most atactic centers are deactivated first.

Pentads

Fig. 5. Effect of the addition of a good external alkoxy silane donor on the microstructure of the boiling heptane soluble fraction of polypropylene.

The increase in size of the syndiotactic rrrr pentad peak of the boiling heptane soluble fractions was unexpected in view of the decrease in the rrrr pentad of unfractionated PP and the boiling heptane insoluble fraction (see Fig. 6). One possible explanation of this apparently unreasonable result is the following: an external alkoxy silane donor preferentially deactivates active centers that produce mainly atactic polymer while leaving active those centers that produce mainly short chain syndiotactic polymer. Simultaneously there is an increase in the production of isotactic polymer with some stereochemical defects, but


without syndiotactic sequences. This same observation has been reported by Soga et al.6) As reported above, we also observed an increase in high molecular mass isotactic polymer.

The boiling heptane insoluble fractions of PP gave similar spectra to PP produced with a large amount of external donor. The amount of non-isotactic defects in the boiling heptane insoluble fraction is clearly vanes with the isotacticity of the unfractionated polymer: as Figure 6 shows, the lower the isotacticity of the unfractionated polymer, the greater the amount of non- isotactic defects or sequences in the boiling heptane insoluble fraction.

Pentads

Fig. 6. Effect of isotacticity of unfractionated PP on the microstructure of the boiling heptane insoluble fraction (I = boiling heptane insoluble fraction in %I.

The spectra of the unfractionated PP and both fractions were dependent on the isotacticity of the polymer, not directly on the structure of the donor. Evidently the differences in the 13C NMR spectra reflect to qualitatively similar effects on the active centers of the catalyst upon addition of donor, only the degree of the effect varying from donor to donor.

7. Structural Effect of Alkmy Silane in MgClz Suppmted Cutahst 97

Effects of thenumber andsize of allrory gmups

A very important factor affecting the quality and amount of polymer formed with alkoxy silane donors is the number of alkoxy groups attached to a silicon atom. The more groups there are the more effective is the alkoxy silane in deactivating active centers. Figure 7 shows the relationship between the number of alkoxy groups and isotacticity and activity. Methylethoxysilanes are suitable for testing the effects of alkoxy groups, because the methyl group are such small substituents that the selectivity of the deactivation between atactic and isotactic active centers is at minimum.

15 r c m 0

F 10 0) Y

c .-

c 100

$ .E 90

0 0.05 0.1 0.15 0.2 0 0.05 0.1 0.15 0.2 DonornEA mole ratio DonorlTEA mole ratio

Fig. 7. Effect of the number of alkoxy groups of methylethoxysilane donors on activity and isotacticity (by extraction): A A Me,(EtO)Si, 0 no donor.

0 Me(EtO)$i, 0 Me,(EtO),Si,

Figure 8 shows the relative sizes of pentad peaks in the methyl carbon region of 13C NMR spectra of PP polymerized with different methylethoxysilane donors. The changes in the spectra are systematic, and a function only of the isotacticity of the polymer. Hence, the number of alkoxy groups does not directly influence the microstructure of PP.

An interesting phenomenon was observed when alkoxy silane had only one alkoxy group. A very small amount of TMES increased the isotacticity determined by boiling heptane extraction to the level of 865, while activity remained at the same level as without external donor. Further addition of the

98 M. Hiirkonen, J. V. Seppda and T. Viiinanen

donor had no effect on isotacticity or activity until the donor/TEA ratio approached 1, at which level free uncomplexed donor is almost certainly present.

Pentads

Fig. 8. Effect of the number of alkoxy groups of methylethoxysilane donors on the microstructure of unfkactionated PP.

These results suggest that a good donor should have at least two alkoxy groups. If there is only one , the single oxygen atom in it forms a stable complex with TEA291 and cannot deactivate any of the active centers.

The size and type of the alkoxy group are also significant factors. Methoxy and ethoxy groups have almost the same effects, but n-propoxy begins to be too large and the achieved isotacticity is low, as seen in Figure 9. The alkoxy group should not be too bulky, because the deactivation of active centers seems to be prevented when the groups attached to oxygen are too large. Figure 10 shows that the isotacticity of PP cannot be raised to a satisfactory level if the alkoxy groups are too bulky. Also, the microstructure of the polymer does not differ significantly when no donor is added and when dimethyldiisopropenoxysilane is used as external donor.

7. Structural Effect of A h Silane in MgClz Supported Catalyst 99

mmmm mmmr rmmr mmrr m m + m m rm m m m n

Pentads

Fig. 9. Effect of the size of alkoxy groups of methyltrialkoxysilane donors on the microstructure of unfractionated PP.

100 - s C .-

0 .- c

C .-

.- c

2 1 I I I

0 0.05 0.1 0.15 0.2 0 0.05 0.1 0.15 0.2 DonormEA mole ratio DonorflEA mole ratio

Fig. 10. Effect of the size of alkoxy groups of dimethyldialkoxydane donore on advity and isotactiCity (by extradon). 0 0 Me,(EtO),Si, 0 Me,(i-Pr~penO)~Si, +v no donor.


The size of the hydrocarbon groups bonded to the silicon atom is a significant factor in the selectivity of deactivation. If the hydrocarbon groups are the right size, mostly the atactic active centers will be selectively deactivated, and the overall activity will not decrease substantially even though isotacticity increases markedly. Figure 11 shows the effects of various hydrocarbon groups on the amounts of boiling heptane insoluble and soluble fractions. Small and even long linear hydrocarbon groups did not deactivate the polymerization centers as selectively as phenyl and especially isobutyl groups.

13C NMR study on the influence of the size of hydrocarbon groups of alkoxy silane donors on the microstructure of the polymer did not reveal any unexpected information. As Figure 12 shows, the isotacticity of the polymer increases when the size of hydrocarbon group increases. The spectra vary with the isotacticity, and the size of the hydrocarbon groups does not directly affect the microstructure of PP.

F 0.10 0.15 0.20

DonormEA mole ratio

Fig. 11. Effect of different hydrocarbon groups of trialkoxysilane donors on the activities of boiling heptane insoluble and boiling heptane soluble PP. W Me(MeO),Si, V V n-Pr(MeO)3Si, * * Dodec(EtO),Si, A A i-Bu(MeO)3Si, 0 0 Ph(MeO),Si, +o no donor.

7. Structural Effect of Alkoxy Silane in MgCIz Suppwted Gatalyst 101

100

80

60

8

40

20

0

1

0

no donor Me(MeO),Si /TEA = 0.1

n-Pr(MeO),Si /TEA = 0.1 i-Bu(MeO),Si /TEA I 0.1

Ph(MeO),Si /TEA = 0.1

mmmm mmmr rmmr mmrr mmrm+rmrr nnnn mr m m m

Pentads

Fig. 12. Effect of the size of the alkyl group of methoxysilane donors on the microstructure of the unfractionated PP.

CONCLUSIONS

Our results suggest that the high performance external donor used in typical modern MgClz-supported high yield Ti-catalyst systems should have two and in some cases three alkoxy groups and relatively large non-linear hydrocarbon groups. If the donor has three alkoxy groups, it performs well as long as the hydrocarbon group is large enough. The hydrocarbon groups need not necessarily be phenyl; bulky non-aromatic groups, such as isobutyls, are very good too. If alkoxy silane has only one alkoxy group, it cannot deactivate active centers of any kind.

The alkoxy groups should not be larger than ethoxy. If secondary or tertiary carbons are present, especially if these are very close to the oxygen atom, the deactivation of active centers becomes sterically hindered.

102 M. Harkonen, J. V. Seppiila and T. Vaananen

The selective deactivation of atactic centers appears to be the most important advantage to be gained from using alkoxy silanes as external donors. Our findings on the microstructure of unfractionated and fractionated polypropylene show that the most atactic centers are deactivated first, after which deactivation is in the order of increasing isotacticity. A clear increase in isotacticity of both the boiling heptane soluble and boiling heptane insoluble fractions was observed when external donor was added.

The findings of this work support earlier claims that the active centers of modern supported Ziegler-Natta catalysts are not adequately described by a simple division into isotactic and atactic types. Not only are centers selectively deactivated, but some new kinds of active centers are formed when external alkoxy silane donor is added. The increase in long chain, mostly isotactic, polypropylene cannot be explained any other way. Evidently the long chain polymer has some atactic defects, but not syndiotactic sequences.

The increase in the syndiotactic rrrr pentad peak of the boiling heptane eoluble fraction as more donor is added (Fig. 51, while at the same time this peak decreased in the boiling heptane insoluble fraction and unfractionated polymer (Fig. 4), might be explained as follows: donors preferentially deactivate mainly atactic centers that also produce some syndiotactic sequences, while leaving active those centers that produce mainly short chain syndiotactic polymer. Correspondingly, decrease in syndiotacticity of the h a c t i o n a t e d polymer and the boiling heptane insoluble fraction might be due to increase in the production of long chain isotactic polypropylene without syndiotactic sequences.

The financial support of this work by the Technology Development Centre (TEKES) is gratefully acknowledged. Special thanks go to Dr. Lucian0 Luciani for his valuable advices.

7. Structural Efiect of Alkoxy Silane in MgCl, Supported Catalyst 103

1) P.C. Bar&, M.A. Noristi, M.A. Schexnayder, in Advances in Polyolefins, Ed. R.B. Seymour, T. Cheng, Plenum Press, New York, 1987, p. 295

2) J.C.W. Chien, Y. Hu, J. Polym. Sci., Polym. Chem. Ed., 26,2847 (1987)

3) A. Guyot, R. Bobichon, R. Spitz, L. Duranel, J.L. Lacombe, in 'Transition Metals and Organometallics as Catalyst for Olefin Polymerization", Ed. W. Kaminsky, H. Sinn, Springer-Verlag, Berlin, 1988, p.13

4) N. Kashiwa, J. Yoshitake, A. Toyota, Polym. Bull., 19,333 (1988)

5) M.C. Sacchi, I. Tritto, P. Locatelli, Eur. Pol. J., 24,137 (1988)

6) K. Soga, T. Shiono, Y. Doi, Makromol. Chem., 189,1531 (1988)

7) T. Keii, E. Suzuki, M. Tamura, Y. Doi, in "Transition Metal Catalyzed Polymerization: Alkenes and Dienes, Part A , Ed. R. Quirk, Harwood Academic Publ., New York, 1983, p. 97

8) J.V. Seppiilii, M. Hiirkhen, L. Luciani, Makromol. Chem., in press

9) For example:

a) Eur. Pat. Appl. 267576, Himont Inc., Inv.: P.C. BarM, E. Albizzati, U. Giannini, G. Baruzzi, L. Noristi; Chem. Abstr. 109,160246t (1988)

b) Eur. Pat. Appl. 250229, Ammo Corp., Inv.: C.R. Hoppin, B.S. Tovrog, Chem. Abstr. 109,7118~ (1988)

c) U.S. 4710482, Shell Oil Co., Inv.: R.C. Job; Chem. Abstr. 108, 113153~ (1987)

d) J. Kokai Tokkyo Koho 88/37104, Mitaui Petrochemical Induetries Ltd., Inv.: M. Kioka, A. Toyoda, N. Kashiwa; Chem. Abetr. 109, 74105d (1988)


e) J. Kokai Tokkyo Koho 88/182306, Toho Titanium Co., Inv.: M. Terano, H. Soga, M. Inoue; Chem. Abstr. 109,231731~ (1988)

0 Ger. Offen. 3644368, BASF A.-G, Inv.: R.A. Werner, R. Zolk, G. Schweier; Chem. Abstr. 109,191061~ (1988)

10) For example:

a) Eur. Pat. 45977, Montedison S.p.A., Inv.: S. Parodi, R. Nocci, U. Giannini, P.C. Barb& U. Scata; Chem. Abstr. 96,200358s, (1982)

b) JP Appl. 81/181019 (1981), Mitsui Petrochemical Industries Ltd., Inv.: M. Kioka, N. Kashiwa; Chem. Abstr. 98, 216212s (1983)

11)

12)

13)

14)

15)

16)

17)

18)

R. Spitz, P. Masson, C. Bobichon, A. Guyot, Makromol. Chem. 190, 707 (1989)

Y. Hu, J.C.W. Chien, J. Polym. Sci., Polym. Chem. Ed. 26,2003 (1988)

S. Tang, in "Catalytic Polymerization of Olefins", Studies in Surface Science and Catalysis, 25, Ed. T. Keii, K. Soga, Elsevier, Tokyo, 1986, p. 165

K. Soga, T. Shiono, in "Transition Metal Catalyzed Polymerizations", Ed. R.P. Quirk, Cambridge University Press, Cambridge, 1988, p. 266

E. Iiskola, "The Role of Donors in Supported Ziegler-Natta Catalyst Chemistry and Stereospecific Polymerization", paper presented in "44th Southwest Regional Meeting, American Chemical Society: International Symposium in Ziegler-Natta Catalyst chemistry", Corpus Christi, Texas, USA, 1988.

A. Zambelli, P. Locatelli, G. Bajo, F.A. Bovey, Macromolecules 8, 687 (1975)

T. Hayashi, Y. Inoue, R. Chfija, Asakura, T., Polymer, 29, 138 (1988)

F.C. Shilling, A.E. Tonelli, Macromolecules 13, 270 (1980)

7. Structural Effect of Alkmy Silone in MgC12 Supported Catalyst 105

19)

20)

21)

29)

A. Zambelli, P. Locatelli, A. Provasoli, D.R. Ferro, Macromolecules 13, 267 (1980)

H.N. Cheng, G.H. Lee, Macromolecules 20,436 (1987)

Y. Doi, E. Suzuki, T. Keii, in "Transition Metal Catalyzed Polymerization: Alkenes and Dienes, Part A , Ed. R. Quirk, Harwood Academic Publ., New York, 1983, p. 737

Y. Doi, E. Suzuki, T. Keii, Makromol. Chem., Rapid Commun. 2,293 (1981)

M. Kakugo, T. Miyatake, Y. Naito, K Mizunuma, Macromolecules 21,314 (1988)

K. Soga, T. Uozumi, H. Yanagihara, Makromol. Chem. 190,31(1989)

Y. Inoue, Y. Itabashi, R. Chiljja, Y. Doi, Polymer 25, 1640 (1984)

M. Kakugo, T. Miyatake, Y. Naito, K Mizunuma, Makromol. Chem. 190,505 (1989)

M.C. Sacchi, 1. Tritto, P. Locatelli, in "Transition Metals and Organometallics as Catalyst for Olefin Polymerization", Ed. W. Kaminsky, H. Sinn, Springer-Verlag, Berlin, 1988, p.123

I. Tritto, M.C. Sacchi, P. Locatelli, G. Zannoni, Macromolecules 21,384 (1988)

E. Iiskola, P. Sormunen, T. Garoff, E. VlihBsaja, T.T. Pakkanen, T.A. Pakkanen, in "Transition Metals and Organometallics as Catalyst for Olefin Polymerization", Ed. W. Kaminsky, H. Sinn, Springer- Verlag, Berlin, 1988, p.113


107

8. Active Center Selection and Propene Polymerization Control with the New Supported Ziegler-Natta Catalysts

R. SPITZ, C. BOBICHON, L. DURANEL (*)and A. GUYOT

CNRS - Laboratoire des Matbriaux Organiques BP 24 69390 VERNAISON (France)

(+) ATOCHEM G.R.L. BP 34 LACQ 64170 ARTIX (France)

ABSTRACT

both necessary with the supported Ziegler-Natta catalysts to achieve the requirements of high activity and stereospecificity. The ILB is not directly involved in the active center. During the catalyst preparation the ILB masks the magnesium chloride surface, blocking the acidic defects. The catalyst is then formed by a selective replacement of the weakest bonded ILB by the titanium tetrachloride, giving thus access to low acidic active centers. The scheme can be considered as an active center selection. High activity is observed when a dynamic selection process results in an accumulation of trapped defects.

Internal Lewis bases (ILB) and external Lewis bases (ELB) are

INTRODUCTION

supported Ziegler-Natta propene catalysts have led to numerous and often confused discussions. The problem is not only complex in itself but it must be considered that, despite the studied systems are apparently similar, they actually correspond to several generations of catalysts. After the second generation Ziegler-Natta catalysts (purple TiCl,, Lewis base and chlorinated alkylaluminium) the first supported systems combine the MgC1, carrier with TiCl,, trialkylaluminium and 1 or 2 aromatic esters. A first aromatic ester is used in the solid component as internal Lewis base (ILB), the second (possibly the same compound) is used complexed with trialkylaluminium as an external Lewis base (ELB). Recent catalysts use a phtalate as an ILB and a silane (with at least 1 alkoxysilane group in the molecule) as an ELB. Many academic studies are restricted to simplified systems with 1 Lewis base only. An explanation of the role of the 2 bases acting together is necessary.

The differentiated functions of the two Lewis bases used with the

108 R. Spitz, C. Bobichon. L. Duranel and A. Guyot

The first family of supported catalysts has been reviewed in different papers, particularly by Pino et al. and Barb6 et al. 2 ) .

Scientific papers on the new systems were recently published in the literature ’-’) . The role of the Lewis bases has been examinated in a number of papers, indicating different functions, essentially leading to an increase in selectivity and often in activity. Different interpretations are found : Busico et a1.6) note : poisoning of the less hindered sites on the solid 7 - 1 1 ) : transformation from aspecific to isospecific talyst ’’). They notice that the problem is complicated by secondary reactions between the solid and the solution. The detailed examination of the interactions in the system is presented by Barb6 et al.2). Concerning the ILB , which is in the scope of our paper, it appears that aromatic esters are chiefly bound to MgCl,, even if issued from a TiCl,-ILB complex 1 4 - 1 6 ) . Ternary coumpounds (TiC1,-aromatic ester- MgC1,) are sometimes reported 1 4 * 1 7 ) . Many authors have established that a major part of the ILB is bound to MgC1, independently from TiC1,1a-21).

) changes in the reducing power of the coca-

The formation of a solid catalyst is a complex process depending on the chemical properties of the solid and on its porous and crystal structures. These different aspects have also been studied, often by X-ray diffraction, giving thus access to the size and organisation of the microcrystals. The activity of the solids is related to the decrease in size of the elemental crystals 2 2 - 2 4 ) . In a previous study, we have established the particular pore structure corresponding to active catalysts and how it depends on the grinding process 2 5 ) .

We have tried to understand how the ILB acts during the catalyst preparation. The catalysts are prepared using techniques previously developed ) . EXPERIMENTAL

different steps will be discussed in the paper. The typical preparation of the best catalysts comprises 4 steps :

The catalyst preparations were previously described ) and the

1 - anhydrous MgClz is milled 6 hours : 2 - the solid is comilled 2 hours with dibutylphtalate 3 - the resulting solid is then comilled 4 hours with TiC1, 4 - the resulting solid is suspended in TiC1, (10 m1.g- ) 2 hours

If washing steps are added, same conditions as in step 4 are

The propene polymerization conditions were also previously

(MgCl,/DBP = 16 (molar) ) :

(MgCl,/TiCl, = 1)

at 80’ C, washed with heptane and dried in vacuum.

used.

8. Effect o f h o r s in Supported Catalysts 109

described 5 ) . The typical conditions are : 70' C, total pressure 4 bars, including 0.1 bar hydrogen, heptane slurry. The cocatalyst components: triethylaluminium (6 mmoles. 1- ' ) and phenyltriethoxysilane (0.6 mmoles .l-') are premixed before contact with the catalyst. The polymerization time is generally 90 min.

JieDtane insoluble fraction (HI %) After polymerization, a fraction of the polymer remains in

solution in heptane. The insoluble polymer is extracted 2 hours by boiling heptane in a Kumagawa. The heptane insoluble fraction is expressed (in percent) as the ratio of the insoluble polymer to the whole polymer (including cold and hot heptane soluble). 2 hour Kumagawa extraction is equivalent on a powder to 24 hour Soxhlet extraction.

REBULTB AND DIBCUBBION

Defects distribution and ac tive cen ters distribut ion on maa nesium

The existence of an active center distribution has been chloride and on the catalv St

postulated for a long time to explain the broad continuous molecular weight distributions (MWD) observed with the Ziegler catalysts in the case of polyethylene, as well as in the case of polypropylene. It is one of the main conclusions of the review of Zucchini and Cecchin 2 6 )

MWD is due to the active center distribution and not to diffusion effects. The result also holds for other catalysts : McDaniel concludes in the same sense in the case of Cr supported catalysis * ' ) .

The idea of a continuous distribution must nevertheless be distinguished from a discrete distribution of sites with different oxidation or coordination states as postulated by Soga 2 8 - 3 0 ) to explain differences in reactivity during olefin copolymerization or to explain stereospecific control. The study of copolymers generally shows heterogeneities of the comonomers distribution within chain or of the chain ends distribution ' ) . Copolymers are easily fractionated by solvents 3 2 - 3 3 ) . Locatelli et al. also conclude to an active center distribution from the examination of the first monomer unit insertion with monomers differing in size 3 4 ) . The distribution corresponds then to a steric hindrance distribution.

A continuous defect distribution must be understood as follows : a distribution of structural defects with different local environment exists on an heterogeneous solid surface like MgC1,. These defects give rise to a distribution of active centers after titanium fixation. Moreover, the titanium fixed on the surface may correspond to 1,2 or several different chemical structures. Among the properties that may distinguish the defects, we have mentioned the steric hindrance, but the acidity (which is possibly related) is easier to characterize. The acidity is evidenced for instance by the displacement of the IR

110 R. Spitz, C. Bobichon, L. Duranel and A. Guyot

carbonyl bands when an aromatic ester is supported on MgClZ2) . Moreover, Pocchi has established that the first aromatic ester units bind to very acidic defects (r > C = 0 : 1620 cm- ’ ) . If more aromatic ester is added, the carbonyl band is displaced toward 1680-1685 cm-‘ and becomes very broad, suggesting a sensitivity to the acidity distribution.

active center selectFQn The idea of an active center distribution easily conducts to an

active center selection. In a simple form, it was clearly proposed by Corradini et al. 6 , . Depending on the crystal face on MgCl, , the ILB binds more strongly or more weakly and is then able to be displaced or not by TiC1,. The catalyst preparation according to the simple scheme of active center selection is then summarized in two steps : (1) masking and (2) unmasking of the surface. Similar ideas were presented with slight differences by other authors. Zakharov et al?# ” ) also conclude that the ILB binds to the most acidic sites which would lead to the formation of aspecific active centers ’ such a simple scheme does not easily lead to good catalysts‘: using milled MgCl,, the catalysts prepared according to the active center selection only have 10 % of the activity of the best ones and the selectivity remains poor (Table 1).

.But the application of

Table 1. Catalyst prepared by successive contact with ILB and TiC1,. MgCl2 has been previously milled 6 hrs

ILB ELB [Al]/[ELB] Heptane insoluble Productivity HI % g/g . cat. h

ethyl- ethyl- 4 93 < 2ooa1 benzoate benzoate

dibutyl- phenyl- 10 phtalate triethoxy-

silane

92 150b ’

polymerization conditions : a) 60’ C : 4 bars : 10 moles 1-j triethylaluminium in heptane

triethylaluminium in heptane b) 70’ C; 4 bars : 6 moles 1-’

ic active center selection The catalyst preparation is in fact a dynamic and not a static

process. The ILB is used to trap transcient defects, which are thus accumulated. Partial unmasking by TiC1, or a chlorinated solvent (1,2 dichloroethane (DCE) for instance) fonns the active centers or prepare their formation.

8. Effect of Donors in Supported Catalysts 111

Table 2. Typical catalyst preparations according to the dynamic active centers selection

MgC1, milling : pretreatment conditionning the initial pore structure

+ dibutylphtalate : comilling : accumulation of defects (masking)

TiC1, comilling : accumulation of sites@

{-b 1/2 DCE washing : TiC1, washing

TiC1, impregnation +L unmasking @

unmasking 0 reimpregnation

Catalyst preparation Ti ILB Productivity' ) HI (%) w/w % w/w % g.g cat.

@ TiC1, impregnation 1.5 12 1300 96.8

@ Tiel, comilling 2.5 15 500 81

@ TiC1, comilling 1.2 11 1200 97

0 + 1,2 DCE washing

TiC1, comilling 4.4 10 2200 96.7

+ TiC1, washing

a) standard polymerization conditions : 4 bars ; 70' C; [Al]/[PTES] = 10 : 90 min.

In order to produce a great number of defects, a preparation using comilling is chosen. Sequences concluding to different solid catalysts are presented in Table 2 , dibutylphtalate (DBP) being used as an ILB. The catalysts are tested with phenyltriethoxysilane (FTES) as an ELB. In process 1, the defects are accumulated during the MgC1,-DBP comilling. Unmasking/impregnation with TiC1, leads to a good selectivity but a rather low activity. To the accumulation of defects can be added the accumulation of potential active centers : in process 2 to 4, the MgC1,-DBP solid is comilled with TICl,.(TiCl,/DBP = 1 (molar)). The resulting solid has poor properties despite it contains the ILB and TiC1,. After a DCE washing (seq. 2 ) , which extracts a part of the titanium and of the ILB : the activity and mainly the selectivity are improved. If TiC1, is used instead of DCE (seq. 3), a TiC1, reimpregnation occurs and activity and selectivity are good together.

112 R. Spitz. C. Bobichon. L. Duranel and A. Guyot

Table 3. Effect of a 1,2 DCE washing following the MgCl,.DBP comilling. The preparation corresponds to Table 2 without prime

Catalyst preparation Productivity HI ( 2 ) g/g . cat.

1' TiC1, impregnation 14 50 93.5

4' TiC1, comilling 650 80

3' TiC1, comilling 1650 90

+ TiC1, washing

Table 3 illustrates the effects of a slight change in the catalyst preparation : an additional DCE washing follows the MgC1,-DBP comilling : the tacticity drops in all cases. A part of the DBP is extracted (about 40 %) before it has plaid his role. When the milling steps are inverted (MgC1, with TiC1, followed by DBP) the catalyst remains poor even after TiC1, washing (A = 1140 g/g cat.h : HI % = 87). The preparation operates against the idea of active center selection and the milling step contacting the 3 components of the solid is not long enough to compensate the inversion and to lead to a common final state.

peturn to 3rd ameration catalysts

Table 4. Catalysts prepared according to the sequences given in Table 2, ethylbenzoate being used instead of dibutylphtalate. Standard polymerization conditions (ELB = phenyltriethoxysilane)

Catalyst preparation MgCl,/EB Productivity HI mole/mole g/g* cat. ( % I

16 800 84.2

16 1900 81

11 1400 90

16 1500 80

The same scheme can be applied to catalysts with an ILB easier to displace than DBP : ethyl benzoate (EB) in Table 4. If used with PTES

8. Efject of Donors in Supported Catalysts 113

as an ELB, the results remain poor when a MgC12/ILB ratio = 16 is used like with DBP. The results are somewhat improved at MgCl,/EB = 11, but the selectivity remains always low. With a different preparation (Table 5) the results are almost the same : MgC1, is comilled with EB (12 hours) then contacted with excess TiC1, (60'C, 2 hours). As it was the case in table 11, TiC1, or DCE washing improves the catalyst but activity and selectivity remain low.

Table 5. Catalysts prepared according to sequence 1 (TiC1, impregnation) in table 2, followed by washing. The ILB is ethylbenzoate.

Catalyst preparation Productivity HI g/ g. cat. ( % I

1 900 80

1 + TiC1, washing 1700 86

1 + DCE washing 1660 90

This indicates that it is very difficult to prepare a catalyst corresponding to the new generation of supported catalysts. Not only the preparation sequence but also the ILB must be adapted. The preparation sequences force equilibria displacements in order to select particular species. It works better with a phtalate, probably because a bidentate reagent is strongly adsorbed on the surface. The selectivity is then determined by the choice and also the concentration of the ILB in the different reaction Steps.

COrJCLUBIO~ The new catalysts using a diester have been prepared with a

strong active center selection. Their activity in the absence of hydrogen is in fact very low : less than a half of the values reported in the tables, but is improved in the presence of hydrogen 5 , . Their potential stereospecificity is so high that they can be used at very high Al/ELB ratios : 10 or more. This is not the case with the older catalysts containing aromatic esters which need Al/ELB ratios, below 4. The crossing of the ILB and ELB of the two families (illustrated in table 6) never gives good results: the best catalyst of each type used with the ELB corresponding to the other catalyst have poor properties.

ILB must be part of the active center. The control of the reaction is possible even in an indirect manner like a selection.

Many authors, as does Soga in a recent paper postulate that

114 R. Spitz. C. Bobichon, L. Duranel and A. Guyot

Table 6. THE ILB-ELB association cannot be interchanged. Crossing reactions using ethylbenzoate and dibutylphtalate as ILB, ethylbenzoate and phenyltriethoxysilane as ELB

Catalyst [Al]/[EB] Productivity HI g/g.cat. (2 )

MgC1, -EB-TiCl, 3 1500 96

MgC1, -DBP-TiCl, 3 700 87

[All/ Productivity H I [PTES] g/g.cat. ( % )

10 800 84

10 2000 97.5

The fact that the ILB is not bound to the active center better

It is then not evident fits with common observations : ILB is bound to MgC1, and is displaced from the solid during polymerization * 0

that the amount of ILB remaining on the solid accounts for the active centers, even if the reported values are not always so high than those observed by Chien et al. ' 1 ' 9 ) : about 25 % of the titanium. The results presented by Ciardelli et al. "'with chiral mono and bidentate Lewis bases used in stereoselective polymerization of racemic olefins are more difficult to understand : the active center selection must work not only according to stereospecificity but also to chirality. Another interest of the study in ref. 40, is that it demonstrates the different roles of ILB and ELB : after exchange, the antipode is polymerized and this agrees with the idea that only one of the Lewis bases belongs to the active center 40.

ACRNOWLEWENEBJTB This work was supported by ATOCHEM-Groupe Elf Aquitaine.

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35. Focchi, citated in : M. Giannini, G. Giunchi, E.A. Albizatti in "Recent Advances in Mechanistic and Synthetic Aspects of Polymerization", NATO AS1 Ser. u, M. Fontanille and A. Guyot Ed., Reidel Dordrecht, 1987, p. 473

36. V.A. Zakharov, A. Sergeev, D. Bukatov, M. Moroz, Makromol. Chem., m, 2421 (1983)

37. S.A. Sergeev, V.A. Polyboyarov, V.A. Zakharov, V.V. Anufrienko, D. Bukatov, Makromol. Chem., L86, 243 (1985)

38. E.P. 86288 to Mitsui Petrochemical Industries (1982) 39. J.C. W. Chien - Communication to the International Symposium

"Transition Metals and Organometallics as catalysts for olefin polymerizationn, Hamburg, Sept. 1987 and J.C.W. Chien and Y. Hu, J. Polym. Sci. Polym. Chem. 26, 2973 (1988)

40. F. Ciardelli, C. Carlini, F. Menconi, A. Altomare, J.C.W. Chien, ibid. ref. 32, p. 109

41. R. Spitz, C. Bobichon, M.F. Llauro-Darricades, A. Guyot, L. Duranel, J. Mol. Cat. (in press)

117

9. Control of the Catalyst and Polymer Properties of Linear Polyethylenes

R. SPITZ , C. BRUN' ) and J. F. JOLY Laboratoire des Materiaux Organiques - CNRS BP 24 - 69390 VERNAISON (France) (*) Groupe de Recherches de Lacq BP 34 LACQ - 64170 ARTIX (France)

ABSTRACT

the molecular weight distribution (MWD) and to the comonomer distribution (CD) among and in the polymer chains. MWD can be controlled by the choice of the solid catalyst. Narrow MWD are obtained using an active center selection decreasing the diversity of the active centers, for instance by the use of an internal Lewis base. The result is generally improved by addition of an external Lewis base. On the contrary, the presence of different classes of active centers gives rise to wide MWD. CD is controlled in some extent by the same factors : however, the selection of a particular class of active centers does not necessarily correspond to the best properties. Composition differences between the chains lead to sticky polymers. CD statistics differing for chains having the same composition change the properties related to the crystallization.

The properties of linear polyethy-anes are essential-y related to

INTRODUCTION Supported Ziegler-Natta catalysts suited for linear polyethylene

synthesis can be prepared using anhydrous magnesium chloride and titanium tetrachloride. The polymer properties are often changed when additives are used with the catalyst or with the cocatalyst. According to the work done with the supported catalysts for propene polymerization, internal Lewis bases ( ILB) associated to the solid catalyst, as well as external Lewis bases associated to the cocatalyst seem to be able to change the behaviour of the system. As a difference with the propene polymerization for which the choice of Lewis bases is generally restricted to a small number of families including aromatic esters, amines and silane derivatives ' ) ) , an extended choice of bases can be expected to have effects. Fewer studies were presented in the case of polyethylene ' ) .

118 R. Spitz, C. B m and J. F. Joly

The properties of a high density polyethylene (HDPE) are essentially related to the molecular weight MW) and molecular weight distribution (MWD). In the case of copolymers, for instance linear low density polyethylene (LLDPE), the comonomer content and the statistics of comonomer distribution( CD) in the chains and among the chains must also be considered. All of these properties are often dependent on the polymerization conditions, the choice of the catalyst and the cocatalyst and the use of internal or external Lewis bases. Most of these properties are in fact related to the active center distribution : broad distributions corresponding to a broad distribution of properties within the chains, narrow distributions corresponding to a selection of the active centers. Broad molecular weight distributions are often assigned to a broad active center distribution5 v 6 ) . A more detailed discussion of the active center distributions and selections is presented in another paper The effect of the ILB is to select among the active centers '). The ELB selects how the active centers will work 8 . EXPERIMENTAL

w v s t g : detailed preparation of a catalyst containing dibutylphtalate (DBP) as an internal Lewis base have been given earl ier . The preparation comprises 4 steps: (1) anhydrous MgClz is milled 6 hours (2) the solid is co-milled with DBP (3) the solid is then co-milled with TiC1, (4) the solid is washed with excess TiC1, at 80' C and then dried under vacuum.

prepared according to the scheme. The molar ratios used are MgCl,/DBP = 16 in step (2) and TiCl,/DBP = 1 in step (3).

All the catalysts comprising an internal Lewis base have been

If steps (2) and (3) are ommitted, a MgCl,-TiCl, (MT) catalyst is obtained.

PAT catalva : 3 g of a MgC12-TiCl,solid are suspended in 50 ml dry n-heptane. 5 ml of pure chlorodiethylaluminium are then added. The suspension is heated 2 hours at 40' C. The brown solid obtained is thoroughly washed with n-heptane, contacted with 30 ml TiC1, 2 hours at 100' C. The color turns then to purple. The two reaction steps correspond to a reduction (R) followed by an allotropic transformation (AT)

m0 ca t a l m : 3 g of a MgCl,-TiCl, solid are suspended in 20 ml of a 1,2 mole/l solution of triethylaluminium in dry heptane. The suspension is heated 3 hours at 40' C. The grey-black solid obtained is washed with n-heptane and contacted with TiC1, like the RAT catalyst. The two reaction steps correspond to a reduction (R)

9. Control of the Catalyst and Polymer Properties of Linear Polyethylene 119

followed by a reoxidation (RO). The RRO solid is purple, indicating that allotropic transformation occurs during or after the reoxidation process.

polvmerizations : * polymerization is achieved in the same conditions previously described for propene polymerization 8 ) , except: temperature 80' C, total pressure 8 bars.

* gas Dhase : gas phase polymerization is achieved in a spherical reactor, equipped with a magnetic stirring. The catalyst is injected in the pressurized reactor containing the cocatalyst (trihexylaluminium : 0 , 7 mmoles), the monomer mixture and hydrogen, preheated to the reaction temperature (generally 85' C). The reactor pressure (10-16 bars) is maintained constant during the reaction time (1 h) by continuous addition of a monomer mixture corresponding to the desired polymer composition. The initial gas phase in the reactor is adjusted to the reactivity ratio between ethylene and butene to avoid any composition drift during polymerization. Typically, a 4 0 molar butene copolymer is obtained from a reactor containing 12-16 0 butene (the value changes with the catalyst) in the monomer mixture, controlled by gas chromatography.

Melt indices are measured at 190' C with 2.16, 5 and 21.6 kg load. The respective values are referred to as MI, , MI, and MI,,. The molecular weight distributions are estimated from melt index ratios : MI2 ,/MI2 , noted MFR (melt flow ratio) and MI, , /MI, , M15/MIZ. Broad MWD correspond to high ratio values (MFR > 60) (MI,,/MI, > 16) and narrow distributions to low ratio values (MFR < 30 : MI,, /MI, < 10 : MI,/MI,

The hexane soluble fraction is obtained by a 4 hour Kumagawa < 3).

extraction.


Molecular weiaht control for HDPE * Slurry polymerization Preparation of HDPE in heptane slurry polymerization results in

differences in gctivity, MW and MWD when different trialkylaluminia are used. The more reactive triethylaluminium (TEA) is able to form the active centers in a rather short time but also to deactivate them. The kinetic curve is of type 3 (fig. 1).

On the contrary, trihexylaluminium (THA) needs a longer time to activate the catalyst but does not destroy the activity, giving rise to type 2 kinetics. The MWD is then generally narrower with TEA and the molecular weight lower (Table 1).

120 R. Spitz, C. Brun and J. F. Joly

Figure 1. Kinetic behaviors observed with the catalytic systems studied in the paper. Kinetics of type I are generally observed in gas phase polymerization : type 2 and 3 in suspension polymerization. Activities are given in arbitrary scale.

u (f

I \ - - - I

I I /'I 1 I I I 1 4 1 0 20 30 4 0 5 0

TIME ( m i n )

Active centers producing high molecular weight polymer are probably destroyed by TEA. The use of different ILB generally results in a selection of active centers ') , especially with the silanes and the dibutylphtalate. The narrowing of the distribution is better demonstrated with THA, the distribution without ILB being broader. The active centers selected are more stable with TEA, giving more activity, but are more difficult to activate with THAI leading to the opposite effect. The examination of different chemical families shows that the result cannot be extended to any compound. The case of p-hydroxymethylben'zoate is particular. It irreversibly binds to the MgC1, surface and cannot be extracted by washing. The activity is then very low.

9. Control of the Catalyst and Polymer properties of Linear Polyethylene 121

Table 1. Heptane slurry polymerization at 80’ C, 8 bar ethylene pressure. Effect of ILB on melt index and melt index ratio with cocatalyst : triethyl and trihexylaluminium [All = 3 mM. 1- ’

I LB Trialkyl- H, Productivity 1 5 ‘2 1 . 6 / ’ 5 (bars) (gP/gcat) (g per 10 min.)

None THA 3 3600 TEA 3 2500

‘6 H5 si (“2 H5 3 THA 3 TEA 3

2700 6300

(C6H5 ),Si(OCH3 ), TEA 3 2600 THA 3.4 1130

Diphenylether TEA 3 1600

C6 H5 CH, SCH, C, H, THA 3

HO - 0 - COOCHS TEA 3

TEA 1.5

COOBu

COOBu

800

200

1330

1 4.2

1.6 3.65

0.55 1.6

9

1.19

1

4.3

1.77

13.2 10

9 8.3

9.4 10.26

8.4

10.33

13.26

11.4

8.5

THA 3.5 685 13 8


The effects of external Lewis bases containing oxygen is given in Table 2.

Table 2. Slurry polymerization at 80' C, 8 bar ethylene pressure. Effect of ELB on productivity, melt-index and melt-index ratio [All = 3 mM.1-l :

Cocatalyst H2 Productivity 1 5 '2 1 .6 / '5 (bars) (gp/g cats) (g per 10 min)

THA THA/ (CC Hp 1 2 0

T m / 9 1 yme THA/dimethoxypropane

THA/diglyme

diph6nyldimethoxysilane

phdnyltriethoxysilane

THA/dibutylphtalate

T M /

THA/

1.5

2

2 2

3.5 3.5

3.5

3.5

3.5 3.5

3.5

3.5

3400 2100

1230

1070

4500

2470

1280 1140

1950

2200

1980

3060

0.74

2.9

1.88

1.3

2.3

2.2

1.4 1.75

2.6

2.44

3.9

2.6

10.5 10.9

9.3

10.1

14.7 13

11.7 11.3

13.7

15.4

14.3

16

The activity of the MgCl2-TiCl4 catalyst used with THA is decreased when an ELB (Al/ELB = 20) is used and the molecular weight narrowed, chiefly when diethers are used. Silane and phtalate have no positive effects. The phtalate undergoes during polymerization a reduction towards aluminium alcoolate like other aromatic esters l o ) .

The changes in medium composition may explain the broad distribution observed. Similar results are obtained with TEA but the variation range is narrow. The same results are also observed when the catalyst contains an ILB but the properties vary in a very short range.

* Gas phase polymerization In gas phase, the polymerization kinetics are always of the first

type. The active centers are not very stable in the polymerization conditions. So, as it could be expected, the MWD are narrower than in slurry. Addition of an ELB also results in an increased stability of the system. Although a lowered maximum polymerization rate is observed, the productivity is often increased at long polymerization times. The viscosity variations presented in Table 3 correspond to similar trends as in slurry : the ILB and the ELB contribute to narrow the MWD.

9. Control of the Catalyst and Polymer Properties of Linear Polyethylene 123

Table 3. Effect of ILB and ELB on productivity melt-index and melt-index ratio in gas phase ethylene polymerization at 95' C.

Catalytic system H2 C2H, P '2.16 'Si'2.16 (bars) (bars) (g/gcat-) (g per 10 min.)

MgC1, dibutylphtalate Cocatalyst : THA

THA + DMP 1/20 THA + PTES 1/20 THA + DMPES 1/20 THA + DMP 1/20

MgC1, -TiCl,

cocatalyst : THA

5 10

6 5

5 10

5 10 5 10 5 10

2.5 5

5 5

16 4

3300

1000

3400

2400 4000 4000

6000

5625 5600

2.7

11.6

2.5

2

3.4 7

1.54

3.1

41

3

2.8

2.8

2.9

2.6 2.6

3.5

3.4

3.3 ~~ ~~ ~~~~

* Broad molecular weight distributions Broad molecular weight distributions are difficult to obtain with

supported Ziegler catalysts but are in fact obtained by many ways . Often, 2 transition metals are associated ' ) or special treatment of the catalyst creates or stabilizes new active centers 6 ) . Limiting the starting transition metal compound to TiCl,, a broad active center distribution is obtained when different states of Ti are present at the same time. Titanium can be used with different valencies (essentially 4 and 3 are useful) and different allotropic forms 1 2 ) .

We have used two ways starting from a MgCl,-TiCl, catalyst : 1) reduction in mild conditions to brown Ti(II1) with A1 (C2 HS ) C1 followed by allotropic transformation to purple Ti (111)

2) reduction to black Ti(I1) followed by oxidation with TiC1,The solids (RRO) obtained in the different steps are detailed in Table 4.

(RAT)

Purple catalysts corresponding to the color of d-TiC1, are obtained in both cases. X-ray synchrotron spectroscopy (XANES and EXAFS) seems to indicate that a major part of the Ti(II1) is really converted to a 6-TiC1, -like strucure' content, the TiC1, final contact (reoxidation or allotropic transformation) is accompanied by Ti(1V) reimpregnation. So, the two solids contain together purple Ti(II1) and TiC1, and perhaps brown Ti(II1). In order to compare the results to simpler systems other catalysts were prepared : the intermediate brown catalyst obtained by the A1Et2C1 mild reduction of the MgCl,-TiCl, solid, noted MgC12-TiC1, (R) and the same contacted with TiC1, for a short time : the conversion to purple does not occur. The solid is noted MgCl,-TiCl, TIC& (RR). A last solid is obtained by comilling MgC1, and 6-TiC1, :

. According to the titanium

MgC12 -6 -TiC1, .


Table 4. Typical synthesie and compositions of the RAT and RRO catalysts

RAT RRO

0 Ti

s m 2 / s Aluminium compound :

( ~ 1 ) mol.1- l Al/Ti

T reduction t

Color TiC1, contact

TiC1, (ml)

T ('C)

t (hr)

solid : 0 Ti Z A1

Composition of the

s W2g Color

2.5

23.4 DEAC

0.7 17.7 40' C 2 h

brown

30

loo

2

3.8 0.8

9

Purple

2.5

23.4 TEA

1.2 15

40'C 2 h

black

30

100

2

11.5 1.5

14.4

purple

The results obtained with these different catalysts in slurry polymerization are collected in Table 5.

Table 5. Slurry ethylene polymerizations with catalysts containing titanium in different forms or oxidation states. The catalysts refered (1) or (2) are prepared from the corresponding MgCl,-TiCl, solids. CocatalyElt : trihexylaluminium ([All = 3 mM 1-')

Catalyst Ti H, Productivity Kinetic Is 12,/Is ( g / g cat.) profile

MqC1, -TiCl, (1)

MgC1, -TiC1, (2)

MgC1, -TiC1, (R) (1)

MgC1, -TiCl, (RR) (1)

MgCl-6 -TiC1,

RAT (1) RAT (2) RRO (2) RRO (2)

1.22 3

2.5 4.3

1.14 3

1.4 3.2

1.88 3

4.7 4.2 3.8 4.3 11.5 4 11.5 4.6

7400

2500

5000

3000

1840

2300 2500 1100 600

I1 1.2

I1 1.3

I1 0.85

I1 1.18

I11 1.6

I11 1.5 I11 0.7 I11 0.6 I11 2.3

13

17

12.5

16

12.7

19 23.4 22 20

9. Control of the Catalyst and P D l p PrOpert'es of Linear Polyethylene 125

Two different starting MgC12-TiC1, solids corresponding to the (1) and (2) indices were used. The two initial catalysts have different Ti contents, different activities and also differ in MWD. The mild reduction with AlEt,Cl has no effect on the distribution. Reimpregnation with TiC1, only has a little effect on the titanium content, and also on MWD (RR catalyst). On the contrary, important changes are observed when the RAT or RRO treatments are used : the Ti content increases to high values. The activity drops but the MWD corresponds to very broad distributions. The broadest distributions are observed with the RRO catalyst.

The same catalysts were used in gas phase polymerization. Results are given in Table 6.

Table 6. Gas phase ethylene polymerizations with catalysts containing mixed valencies of titanium.For definitions (1) and (2), see table 5.

Catalyst T 'C Ethylene H, P '5 '21/'5 pressure pressure g/g cat.

MgC1, -TiCl, (1) 85 10 4 4500 0.9 12

(1) 85 10 4 1800 0.8 13

RAT (1) 85 14 4 2400 0.4 13.7

RRO (2) 80 5 4.5 2000 1 16

RRO (2) 95 5 5 2500 3 15

The same trends are observed in the case of the reduced reoxidated solid : low activity, higher molecular weight, broader distribution. The distributions are, by far, narrower than in slurry, so that the difference in MWD between MgCl,-TiCl, and the RAT catalyst are negligible. The results confirm that it is by far more difficult to obtain broad MWD in gas phase than in slurry.

8 Linear low densitv D olvethvlene D r e D D d bv ethylene - butene - 1 aa phase coDolymerhtion

* Activity and MWD control In copolymerization, the activity is higher than in ethylene

polymerization. The kinetics are always of type I. Typical productivities after 1 hour polymerization are given in Table 7 in polymerization conditions producing a copolymer with a density near 920 kg/m3 .

126 R. Spitz, C. B m and J. F. Joly

Table 7. Typical productivities in kg/g cat. in gas phase ethylene-butene copolymerization. Experimental conditions are : duration : 1 hr : monomer pressure : 10 bars : hydrogen : 1.5 to 2.5 bars : temperature : 85' C : cocatalyst THA : 0.8 mM in 2.5 liter reactor. The monomer ratio is adjusted to a constant value in the reactor during polymerization. The productivities correspond to roughly 4.5 Z molar butene in the polymer.

Catalyst A Kg/g . cat.

MgCl, -TiCl, 6 - 15 MMgCl2-dibutylphtalate-TiC1, 8

MgClz-phenyltriethoxysilane-TiClb 20

MgCl, -TiCl, -Tiel, 3 - 10 (RRO or RAT)

Activities are depressed in the presence of an ELB. The MW are always lowered. The presence of butene enhances the transfer reaction with hydrogen" ) . The MWD are narrower than in homopolymerization and often vary with the butene content with the same trend : butene decreases MW and narrows MWD. Results are summarized in Table 8.

Table 8. Gas phase ethylene-butene copolymerization at 85' C. Effect of the catalyst and butene content on melt index and melt flow ratio (12,.6/12.16) at different comonomer content given by the number of ethyl branches. PTES, DPDMS and DBP are respectively for phenyltriethoxysilane, diphenyl-dimethoxysilane, dibutylphtalate.

Catalyst C,~/lOOO C I,. MFR

MgClz -PTES-TiCl, 14 1.6 33

17.5 2.1 33

MgCl, -DPDMS-TiCl, 17 1.1 29

MgCl, -DBP-TiCl, 18.1 2.2 28

MgCl, -TiCl, 14.1 0.5 37 34.5 4 26

17.5 1.5 40 21.4 3 34

MgCl, -TICl, -Tiel, 21.6 0.5 63"

RRO 20 2.6 48

17.1 1 65b)

12.6 0.5 70 a) t = 60' C : b) 65' C

9. Control of fk Catolpt ond Polymer Properties of Lineor Polyethylene 127

Narrow MWD are obtained when an ILB is used, while broader distributions are observed if different titanium chloride species are present on the catalyst. The broader distributions are very sensitive to the temperature and the butene content.

Narrowing effects are also observed with ELB. Results are examplified in Table 9.

Hydrogen was adjusted in order to maintain the 2.16 kg melt index near 1 g per 10 min. The effect of Lewis bases chosen in different chemical families is presented at different butene contents. Most of the ELB induces a MWD narrowing. Good results are obtained with ethers for instance. The best melt flow ratio indices are very low : 22 to 24.

Table 9. Gas phase ethylene butene polymerization (85' C ; 10 bar total pressure) : effect of butene content and ELB on the me'lt-flow ratio. The solid catalyst used cotnains dibutylphtalate as an internal Lewis base.

Lewis base C, H,/1000 C I,. MFR g per min.

diphenyldimethoxysilane (DMPS) 24.7 2 26 THF 23.5 0.7 22

Without ELB 22.8 1.6 29 dibutylphtalate 20.7 0.5 24

DMPS 19.4 1.1 24 ( ' 4 % ) Z 0 18.9 1.5 24

Without ELB 18.1 1.5 27

( c 4 % ) Z 0 17.2 0.7 24

diglyme 16.8 0.9 24

2,2 dimethoxypropane 15.5 0.7 22 dioxanne 14.7 0.7 23

piperidhe 14.3 1 26

* Heterogeneity of the copolymer The copolymer composition and heterogeneity determines the

properties of the product. The variations in composition between the polymer chains can be studied by T.R.E.F. 1 5 - 1 6 ) . In fact, it appears generally that the copolymer is a mixture of two fractions : a low comonomer-content fraction and a high comonomer-content fraction. Such a fractionation is easily obtained in one step solvent extraction. In a previous study using SiO, bi-suppported catalysts, we have shown that a boiling hexane fractionation extracts a well-defined fraction,


almost not sensitive to the MI and to the catalyst but sensitive to the butene content : the soluble fraction varies as a function of the square of the comonomer in the whole polymer 0 ' . Most of the polymers obtained with the catalysts studied in this paper are on the same curve without ELB. With ELB soluble fractions are sometimes far below the common values : it is the case with cyclic ethers for instance. For instance : 5.7 % soluble (THF) instead of 15 % (no ELB) when the polymer contains 23.5 methyls (Table 10). Such a polymer will not be sticky.

Table 10. Gas phase polymerization at 85' C. Effect of the catalytic system on the hot hexane soluble fraction and on the fraction composition. DMP is for 2,2 dimethoxypropane. For other abreviations, see table 8.

Catalyst/cocatalyst ethy1/1000 C soluble fraction ethy1/1000 C whole polymer ( % I hexane fraction

MgC1, -TiCl, cocatalyst : THA

MgC1, -PTES-TiCl, cocatalyst : THA

THA : DMP THA : diglyme

MgC1, -DBP-TiCl, cocatalyst : THA

THA : DMP THA : diglyme THA : DPMS

RRO cocatalyst : THA

THA : PTES

MgCl, -VCl, THA

14.1 22

17.5 18 16.8

20.5 13 13.2 24.7

20 17.7

18.4

5.4 14

5.5 10.4 8

10.6 4.6 4.5 19.2

15

7.6

20

66

66

62.5

53 57

58

58 57 54.5

68

63

49

The examination of the butene content in the soluble fraction of the polymer brings new information : it was previously found 1 7 ) that the butene content in the hexane soluble fraction is almost independent from the butene in the whole polymer in the L.L.D.P.E. range and also on the molecular weight of the polymer (M12<10). All the values measured on polymers prepared with the silica bi-supported catalyst ranged between 53 and 62 ethyl branches per 1000 carbons.

9. Control of the Catalyst and Polymer PrOpertieS of Lineur Polyethylene 129

Differences are found when different catalysts are used : the soluble fraction contains less branches when an ILB is used, and more branches with the llheterogeneousll catalyst containing titanium in different states (Table 10). The use of an ELB also depresses the butene content.

The trends observed also correspond to the control of the MWD. In order to be sure that the differences in solubility are not directly related to the MWD, a MgCl,-VCl, catalyst is presented for comparison. A MFR of 60 is obtained with the vanadium catalyst, but the number of branches (49/1000 C) is the lowest observed in the L.L.D.P.E. range.

The differences in solubility are then only due to the comonomer distribution in the polymer and not to a molecular weight effect. The meaning is then clear : differences in statistics of the branches distribution change the polymer solubility. If the distribution of branches is regular, as it is probably the case with a vanadium catalyst which generally leads to rather ideal copolymerization ' ) , less branches are necessary to destroy the crystallinity of the polymer and allow dissolution. The same phenomenon will also play a role on the control of the lucomonomer efficiencyuu, i.e. the density variation versus comonomer content. This will be detailed in a further paper.

CONCLUSION

Selection effects acting on the catalyst or the oocatalyst, control the active center population of the Mg supported catalysts. These effects can be used to monitor the MWD. In slurry polymerization, narrow to very broad molecular weight distributions are thus achieved. The same monitoring works in gas phase in a different range : from very narrow to medium, but very broad distributions are not easily found : some active centers are not stable in gas phase polymerization conditions. At the same time, the composition of the ethylene-butene copolymers varies : a narrow MWD is generally associated to a low hexane soluble fraction and to a lower butene content in the soluble polymer. The selection does not only work according to the molecular weight but also according to the reactivity toward comonomer.

ACXNOWLDEQEMENTS

support and help. The authors are indebted to ATOCHEM - Groupe Elf Aquitaine for

130 R. Spitz. C. Brun and J. F. Joly

RBIBREMCEB 1. P.C. Barb&, G. Cecchin, L. Norisiti, Adv. Polym. sci.,

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R. Nocci, U. Giannini, P.C. Barbe, v. Scata ; Chem. Abstr., 181808V (1982)

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aspects of polymerizationo1, ed. by M. Fontanille and A. Guyot, Nato AS1 Ser. C. Reidel a, 485 (1987)

Polymerization of olefins8s ed. by T. Keii, K. Soga, Kodansha Elsevier Amsterdam, 1986 p. 147

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131

10. Easy Conversion of Aspecific into Isospecific Sites

KAZUO SOGA & JOON RYE0 PARK

Research Laboratory of Resources Utilization, Tokyo Institute

of Technology, Nagatsuta, Midori-ku, Yokohama 227, Japan

ABSTRACT

A donor-free MgC12-supported TiC13 catalyst with an

extremely low titanium content was prepared from TiC13.3Py

(pyridine) and MgC12 in the presence of A12(C2H5)3Cl?. The

catalyst combined with A1(C2H5)3 selectively gave atactic

polypropylene. Carrying out the polymerization of propylene

in detail by modifying this catalyst, it was found that the

catalyst isospecificity can be easily converted from

completely aspecific to highly isospecific either by adding a

suitable Lewis base or by using C P ~ T ~ ( C H ~ ) ~ in place of

A1(C2H5I3. The structures of aspecific and isospecific sites

are discussed based on the results with emphasis on the role

of the Lewis base.

INTRODUCTION

Since the discovery of the Ziegler-Natta catalyst,

tremendous research efforts have been aimed at improving

catalyst isospecificity. This effort has yielded new genera-

tions of Ziegler-Natta catalysts with superior isospecifici-

ty. Today, it is well known that catalyst isospecificity is

dramatically improved by using suitable Lewis bases such as

e thy 1 benzoate , e t c. -5) However, the complexities arising

from the heterogeneity of common catalyst systems have

hindered understanding of the role of such Lewis bases.

For example, ordinary MgC12-supported TiClq catalysts

combined with A1(C2H5I3 do not show high isospecificity, but

they give at least 20 wt% isotactic polypropylene even in the

132 K. Soga and J. R. Park

absence of any Lewis base. Thus, these catalysts originally

contain at least two kinds of different active species which

differ in isospecificity.

We have recently prepared a completely aspecific

ca talyts t which selectively produces a tac t ic polypropylene.

The catalyst seems to be very useful for understanding how to

convert the aspecific into isospecific sites. From such a

viewpoint, we conducted propylene polymerization by modifying

this catalyst.

EXPERIMENTAL

- Materials Propylene (from Mitsubishi Petrochemical

Co.) , MgC12 , titanium-reduced TiC13 (from Toho Titanium Co.) A1(C2H5I3 and A12(C2H5I3Cl3 (from Toso-Akzo) were used

without further purification. Research grade heptane and

ethylbenzoate commercially obtained were purified according

to the usual procedures. Cp2Ti(CH3 l 2 was prepared according

to the literature reported by Clauss et a1.,7) diluted into

0.25 mol/dm3 in heptane and stored as stock solution.

Preparation of the aspecific catalyst TiC13.3Py (Py:

pyridine) was prepared from the reaction of TiC13 with

stainless steel vibration mill pot with 50 balls ( 2 5 m m in

diameter) under nitrogen for 48 h at room temperature. The

mixture of the resultant MgC12 (15 g, 97 m2/g) and TiC13 3Py

(54 mg) was treated with an excess amount of A12(C2H5)3C13

(15 mmol in heptane) to obtain the TiC13/MgC12 catalyst. It

was confirmed from the elemental analysis that pyridine was

completely removed from the catalyst.

Polymerization analytical procedures Polymerization

of propylene was conducted either in a 200 cm3 glass reactor

or in a 100 cm3 stainless steel autoclave equipped with a

magnetic stirrer. Polymerization was terminated by adding a

dilute hydrochloric acid solution in methanol. The polymer

produced was fractionated by extraction with boiling heptane

for 10 h to determine the isotactic index (1.1.). The

pyridine at room temperature. MgC12 was ground in a 1 dm 3

10. ConversMn of Catalyst IsospeCficity 133

molecular weight distribution of the polymer was measured at

14OOC by GPC (Waters 15OOC) using o-dichlorobenzene as

solvent. The 13C NMR spectrum of the polymer was recorded at

12OoC using a JEOL GX-270 spectrometer in the pulse FT mode.


The content of Ti in the MgC12-supported TiC13 catalyst

was extremely small (0.043 wt%). It is assumed, therefore,

that most of the TiC13 molecules are separately supported on

the MgC12 surface to form the mononuclear species having two

uncoordinated sites. Since the oxidation state of active Ti

for propylene polymerization is Ti3+,8) addition of A1(C2H5)3

to the catalyst may give an aspecific active species such as

the one shown in Figure 1.

c1

Figure 1 . Plausible mechanism for the formation of active

species in the TiC13/MgC12-A1(C2H5)3 catalyst system.

In fact, polymerization of propylene with this catalyst

system gave totally atactic polypropylene as reported previously. 6)

Modification of the catalyst was attempted either by

changing the cocatalyst from A1(C2H5)3 to Cp2Ti(CH3I2 or by

the addition of e thy1 benzoa te.

Polymerization of propylene was first performed with the

TiC13/MgC12-Cp2Ti(CH3)2 catalyst system. The results

obtained are shown in Table 1. It is obvious from Table 1

that the catalyst isospecif icity is completely changed from

aspecific to isospecific by replacing A1(C2H5)3 with


C P ~ T ~ ( C H ~ ) ~ . Table 2 shows the pentad sequence distributions

of whole and boiling heptane-insoluble polypropylene produced

with the TiC13/MgC12-Cp2Ti(CH3)2 system, indicating that the

catalyst isospecificity is very high.

Table 1. Results of propylene polymerization with the TiC13/MgC12-Cp2Ti(CH3)2 catalyst system a)

b) Act ivi t y 1.1. 3 Cocatalyst (mmol/dm )

(Kg-PP/g-Ti. h ) ( % I

Cp2Ti( CH3 l2 2.5 0.78 23.6

10.0 5.85 93.0 I,

II 20.0 6.30 95.5

,I 35.0 5.70 96.0 ................................................. Al( C2H5 13 c, 20.0 127.0 0

a) Polymerization was conducted at 40°C for 1 h in

a 100 cm autoclave using 0.3 moles of propylene,

250 mg of TiC13/MgC12, and 100 cm3 of heptane

polypropylene

3

b) Weight fraction of boiling heptane-insoluble

c For reference.

Table 2. Steric pentad sequence distributions of polypropylene

produced with the TiC13 /MgC12 - Cp2 Ti ( CH3 ) catalyst s ys tem . a) Polymer fractions

mmrm mmmm mmmr rmmr mmrr rmrm rrrr mrrr mrrm rrmr

Whole polymer 89.4 3.0 0.6 1.8 1.2 0.3 2.1 0.7 0.9

C7-insoluble 94.5 1.6 0.3 0.7 0.6 0.2 1.2 0.4 0.5

a) For the polymer obtained with 20 mm01/dm3 of Cp2Ti(CH3)2

The model illustrated in Figure 2 may be plausible for

the formation of isospecific species between the TiC13/MgC12

catalyst and Cp2Ti(CH3I2. Judging from the observations that

10. Conversion of Catalyst Isospecaficiiy 135

the combinations of Cp2Ti(CH3I2 and A1RnC13-, as well as

C P ~ T ~ ( C H ~ ) ~ and MgC12 are inactive for propylene polymeriza-

tion, the active titanium is considered not to be tetravalent

but trivalent 0. This hypothesis is supported by the fact that the oxidation state of active Ti for propylene

polymerization is Ti3+.8) Since the Ti has only one uncoor-

dinated site, it can selectively give isotactic polypro-

pylene.

c1

Figure 2. Model of isospecific sites formation.

Propylene polymerization was then performed using TiC13/

MgCl2-A1(C2H5I3 catalyst system by the addition of ethyl-

benzoate (EB). The results obtained are shown in Table 3.

Table 3 . Results of propylene polymerization with the TiC13/MgC12-A1(C2H,)3 catalyst system. a)

~~ _____

EB Activity 1.1.

(Kg-PP/g-Ti. h ) (8) 3 (mmol/dm )

0

1.0

2.0

4.0

10.78 0

5.00 73.0

3.76 84.6

3.11 94.4 ~

a) Polymerization was conducted under atmospheric 3 pressure of propylene at 4 0 ° C for 1 h in a 200cm

glass reactor using 250 mg of TiC13/MgC12, 1 mmol

of A1(C2H5)3 and 100 cm3 of heptane.


The [ m m m m ] pentad sequence distribution of the boiling

heptane-insoluble polypropylene w a s approximately 95%.

Figure 3 shows the molecular weight distribution curves of

the polymers obtained with different concentrations of EB.

I - I. The whole polymers Mn K w / Ki

( A ) o . 9 8 * i o 4 7 . 0 7 (B) 2 . 3 3 ~ 1 0 9 . 4 6 (C) 8 . 5 4 r 1 0 4 6 . 7 8

11. The fractionated polymers from sample P-3 Ki Kw I rjrn (D) 0 . 8 7 ~ 1 0 ~ 8 .27 (E) 5.12x10 4.64

103 104 106

Figure 3 . Molecular weight distribution curves of the polymer

obtained with TiC13/MgC12-A1(C2H~)3/EB catalyst system.

(A)EB=O; (B)EB=Z.O; (C)EB=4.0 mOl/dm3

(D)Boiling heptane-soluble; (Elboiling heptane-insoluble part.

10. Caversian of Catalyst IsosPecificCity 137

The molecular weight of whole polymer increased dramatically

with an increase in the EB concentration. That of atactic

polymer (boiling heptane-soluble part), however, remained

almost unchanged. The increase in the molecular weight of

isotactic polymer may be mainly attributed to a decrease in

the concentration of a transfer reagent, A ~ ( C ~ H S ) ~ , by the

formation of the A1(C2H5)3-EB complex. '-lo) The mechanism

for the conversion of aspecific species into isospecific ones

with the help of EB can be shown as follows (Figure 4 ) .

aspecif ic isospecif ic

Figure 4 . Plausible mechanism for the formation of

isospecific active species in the TiC13/MgC12-

A1 (C2H5) 3/EB catalyst system.

Thus, it was found that an aspecific catalyst can be

easily converted into an isospecific one either by replacing

the cocatalyst or by using ethylbenzoate. It is well

recognized that the propagation rate constant of isotactic

polymerization is several times faster than that of atactic

polymerization. The present results, therefore, indicate

that only some aspecific species can be converted into iso-

specific ones; the rest are deactivated. Such a deactivation

may also occur in commercial catalysts, suggesting that

catalyst efficiency could be much improved if this problem is

overcome.


REFERENCES

1. P.Pino, R.Mulhaupt, Angew.Chem.Int.Ed.Engl.,~, 857(1980)

2. V.Bisico, P.Corradini I L.DeMartino, A.Proto, V.Savino,

E.Albizzati, Makromol.Chem., 186, 1279(1985) 3. K.Soga, T.Shiono, Y.Doi, Polym.Bull., 10, 168(1983) 4. K.Soga, T.Sano, K.Yamamoto, T.Shiono, Chem.Lett.,

5. A.W.Langer, T.J.Burkardt, J.J.Steger, in "Transition

Metal Catalyzed Polymerization"; R.P.Quirk Ed., Harwood

Academic Publishers, New York, p421(1983)

425( 1982)

6. T.Shiono, H.Uchino, K.Soga, Polym.Bull., 2 l , 19(1989)

7. K.Clauss, T.Bestian, Justus Liebigs Ann.Chem., g , 654( 1962)

8. K.Soga, T.Sano, R.Ohnishi, Polym.Bull., 4, 157(1979)

9. T.Keii, E.Suzuki, M.Tamura, Y,Doi, in "Transition Metal

Catalyzed Polymerization," R.P.Quirk Ed. I Harwood

Academic Publishers, New York, p83(1 983)

10. R.Spitz, J.L.Lacombe, J.Polym.Sci.Part A, 22, 2611(1984)

1 1 . N.Kashiwa, J.Yoshitake, Polym.Bull., l2 , 99(1984)

139

1 1. A 13C CP- MAS NMR and Elemental Analysis Study of Adsorp- tion of Silyl Ethers on the MgC12- Supported Ziegler -Natta Catalysts

Pekka Sormunen', Tuula T. Pakkanenb, Eila V&hbarjab, Tapani A. Pakkanenb and Eero Iiskola"

'Polyolefins R & D, Neste Chemicals, SF-06850 Kulloo, Finland bDepartment of Chemistry, University of Joensuu. SF-80101 Joensuu, Finland

ABSTRACT

We describe here our results from a 13C CP-MAS NMR and elemental analysis study of adsorption and interaction of a silyl ether, RSi(0Me)s (R = Ph), as an internal and an external electron donor with a MgCIz-supported Ziegler-Natta catalyst. A chemical activation of anhydrous MgC12 with EtOH and AIEt3 produces a high surface area support stabilized by an organoaluminium compound, AIEtAOEt). In a treatment of the thus obtained MgClz with silyl ether the aluminium surface complex is retained and silyl ether is almost totally incorporated into the support. The effects of Tic14 and AIEt3 treatments are also discussed.

INTRODUCTION

Organic Lewis bases are widely used as electron donors in the third generation supported Ziegler- Natta catalysts for alpha-olefin polymerization to enhance activity and to improve stereospecificity.' ' These catalysts comprise a solid catalyst, MgCl2/TiCl4/electron donor (=ED), and a cocatalyst, an aluminium alkyl usually complexed with an electron donor.

The role of the Lewis base as internal and external electron donors is not well understood. The electron donor may have several functions : to complex or to react with MgC12, Tic14 and the aluminium alkyl and to inactivate the nonstereospecific polymerization sites." We have chosen silyl ethers, a recently found3e4) group of active promoters, as the electron donor to probe the interaction mechanism between the Lewis base and the cocatalyst and between the Lewis base and the solid catalyst.

EXPERIMENTAL

Preparation and manipulation of the solid catalysts were all carried out under a dry, oxygen free nitrogen gas (99.998 %) using standard inert atmospheres techniques. m. Solution NMR spectra were recorded on a Bruker AM-250 spectrometer operating at

62.9 MHz for 13C-NMR and at 49.7 MHz for %-NMR. The 13C CP-MAS NMR experiments were

140 P. Sormunen, T. T. Pakkanen. E. Vahasarja and E. Iiskola

conducted at the same spectrometer equipped with an auxiliary high-power amplifier and a narrow bore solid state probe with magic-angle spinning capability.

The powder samples were placed in a glove bag in two-piece boron nitride/deldrin rotors. The deldrin end caps of the rotor provide a 13C signal at 89 ppm. The magic angle was set by using the TPBr signal of KBr. The Haartman-Hahn matching condition for cross-polarization (CP) was calibrated with adamantane. The "C CP-MAS spectra were obtained at a spinning speed of 4.7 - 4.8 kHz using a 14 kHz spectral window with 2.44 Hz data points. The single-contact pulse sequence used a 3 ms contact time (unoptimized). The proton field used for dipolar decoupling during the acquisition time was 10 G. Between 1000 and 20000 scans were normally acquired with a 5s recycle delay. The chemical shifts are reported relative to TMS with use of an external sample of adamantane as reference.

The C and H analyses were done on a Carbon, Hydrogen, Nitrogen Analyzer CHN-600 (Leco Corporation). Samples were weighted in dry nitrogen atmosphere into small copper samples holders. The samples were burned in oxygen.atmosphere at 950'C. and hydrogen was detected as H20 using an IR cell and carbon as C02 by another IR cell.

Samples for the Mg, Ti and Al analysis were dissolved in I:l hydrocloric acid. The metal ions were determined with a Perkin Elmer 1100 Atomic Absorption Spectrometer.

The chlorine content was measured with argentometric titration from the samples dissolved in

Surface area determiartioa. The surface areas were determined by the BET method with Accusorb 2200 (Micromeritics) according to the standard ASTM D 3663-78.

b c t l v u of MPCI~ . To a slurry of anhydrous MgCl2 ( I mol) in hexane was added dropwise 3 moles of anhydrous ethanol at ambient temperature. The mixture was stirred for 24 hours. The solution was decanted, the remaining solid was washed with hexane and dried in vacuum. The thus obtained MgCI2*3EtOH was treated twice with AIEt3 in hexane to remove the alcohol. The product was separated from the liquid with decantation, washed with hexane and dried in vacuum. Anal. Found: Mg, 13.3; CI, 52.4; Al, 4.1.

C h e & a h d y & m

7.5 N H$Ob.

Characterization of the "active" MgClz gave a surface area of 460 m2/g. a of rl Ivl ether on MnCb The "active" MgC12 was stirred for two hours with an

electron donor in hexane at room temperature in a 1: 0.5 mole ratio. The product was repeatedly washed with hexane and dried in vacuum.

The product (7 g) obtained in the previous step was reacted with Tic14 (52 g) in hexane at the reflux temperature for 2 h. The light brown solid was separated, rinsed with hexane and dried in vacuum.

The solid from the former step (2.5 g) was treated with AIEt3 in a 150 or 1:IO Ti/AI molar ratio in hexane. The mixture was stirred at 50°C for 1 h. The thus obtained black solid was washed with hexane and dried in vacuum.

The Tick treat ment of the crtrlrst .

The AIEt. activ&loa o f the catalyst .

11. Analysis of Sib1 Esters on Mgclz Supported Catalysts 141


3. At ambient temperature silyl ethers of the type RSi(0Me)s form with the AIEt3 cocatalyst in solution instantaneously a donor acceptor complex. The resonance of the methoxy group of PhSi(0Me)s has shifted ca. 2 ppm downfield with respect to the uncomplexed silane signal (Figs. 1. and 2.). A single 13C signal is observed for the complexed and uncomplexed, magnetically inequivalent methoxy carbons. This averaging is assumed to be due to a rapid chemical exchange interconverting them.

The thus formed presumably 1:l complex , e.g. PhSi(OMe),*AIEt3, is relatively stable under an inert atmosphere even at elevated temperatures provided that the AIEt3 : silyl ether ratio is one. However, in the presence of excess AIEt3 the complexes between AIEt3 and silyl ethers containing more than one methoxy group (n) readily rearrange and are subjected to alkylation n-1 t i r n e ~ . ~ ' ~ )

The chemical activation of the MgC12 support of the catalyst was performed by treating anhydrous MgClz with an activating agent, ethanol. The "active" MgCl2 was obtained by a subsequent reaction of MgC12*3EtOH with AIEt3. According to chemical analysis the "active" MgC12 contains 4.7 wt-% aluminium (Table 1.). which on the basis of the 13C CP-MAS NMR data (Fig. 3.) was identified as A1Eti?(OEt).7' This species can be formed in a reaction between EtOH and AIEt3.

m i c a 1 retivlfjpp of the MnCh suDsort .

Table 1. Changes i n Chemical Carposition a t the Stages of Preparation of MgCl2 - sLpported catalyst

with PhSi(Olle)3 as the electron donor (ED).

Hater i a l Caposition, w t -% Mole ra t io of conponmts SUET Mg C l T i A1 C H 110 C l T i A1 ED $0-1

MgC12 13.3 52.4 . - 4.7 c c 1 2.7 0.3 460 MgClZ/ED 10.8 31.0 - 3.0 27.6 6.5 1 2.0 0.25 0.41' 33 MgC lz/ED/T i Cl4 11.6 50.0 5.9 2.9 13.2 2.1 1 3.0 0.26 0.22 0.21b 130 MpC Iz/ED/T i C 14/TEAd 0.9 46.0 5.3 4.0 11.8 2.8 1 2.4 0.19 0.26

'mtnmt of the electron donor ( E D ) calculated assming A 1 as AL(Et)EtZ. bnount of the electron donor (ED) calculated assming A1 as Al(Et)CL2. Cnot determined %i : A 1 = 1 : 50 i n the activation, TEA = A l E t j

Adsorption of AIEtAOEt) is proposed to take place by coordination of the ethoxy oxygen to Mg2* on the 110 face of the MgC12 lattice. The broad "C signals of AIEtAOEt) are indications of heterogenous nature of the coordination sites on the MgCI2 surface.

The incorporation of PhSi(0Me)~ as an internal donor into the "active" MgC12 support was performed in a 2 1 MgClz : ED ratio. The results of

Adsomtion of elect con dono r on MeC12 .

142 P. Sonnunen. T. T. Pakkanen, E. Vahasarja and E. Iiskola

elemental analysis (Table 1 .) indicate almost a quantitative adsorption of electron donor onto MgCI2. In addition, the organoaluminium compound is retained on the support.

The 13C CP-MAS spectrum (Fig. 4.) shows signals of the MgC12 - attached AIEtAOEt) and a single broad resonance at ca. 50.7 ppm due to silicon bound methoxy carbon and the resonances of the aromatic carbons of PhSi(0Me)p The methoxy resonance is only slightly shifted from the 13C isotropic chemical shift of the liquid silyl ether at 50.6 pprn (Table 2.). Most of the electron donor held on the MgC12 support can thus be considered as "intercrystalline fluid" ') which does not experience a strong interaction with the support.

Table 2.

PhSi(OMe)3 at the stages of the preparation of MgCl2 - supported catalysts. 13C Chemical Shift (in ppm from Si(Me)4) of the "C resonance of the OCH3 group of

Material ED = PhSi(OMe)3

50.7

53.4

53.2

50.6

53.6

Ti:AI = 150 in the activation

TiCL treatment of the crtrlvJt . The Tic14 treatment of the MgCl2 material is associated with displacement of almost half of the electron donor content (Table 1.). The Tic14 treatment removes also some of the aluminium incorporated to MgCIE After this the AkED molar ratio is close to one. The 13C CP-MAS spectrum (Fig. 5.) shows only the resonances of PhSi(0Me)s. A single methoxy signal, which has shifted 2 ppm downfield upon Tic14 treatment, is observed for the complexed and uncomplexed OMe groups. The carbon signals of the aluminium compound are poorly observable or no longer visible. Chlorination of AlEtAOEt) by Tic14 is proposed to have occurred. The silyl ether does not seem to be directly bound or complexed to titanium since the shift of the methoxy resonance is not large. The titanium bound OMe species are known to resonate at 72 - 76

ppm. In addition, in solution silyl ethers do not form with TIC16 stable isolable complexes, but undergo with Tic14 an exchange r ea~ t ion .~ ) The chemical shift of the the methoxy resonance at 53.4

ppm equals that of PhSi(OMe)3*AIEt3 found in solution. This result together with the observed AkED mole ratio of 1 support an 1:1 type coordination between A1 and the silyl ether.

After an AIEt3 activation of the catalyst the Ti-content has decreased and the aluminium content increased (Table I .). The 13C CP-MAS spectrum (Fig. 6.) of the activated catalyst contains unexpectedly a methoxy signal at 53.2 ppm of very low intensity in regard to the intensities of the methoxy and phenyl signals. The chemical shift of the methoxy

AlEtr - .ctivrtioa of the I .

11. Analysis of S l y 1 Estns on MgCl, Suppolted Caitalysts 143

signal is nearly equal to that of the complexed silyl ether in solution. Thus most of the silyl ether can still be considered complexed to the aluminium site of the MgClz support. The low intensity of the methoxy resonance may arise from a gradual alkylation of PhSi(0Me)s by AIEtp

CONCLUSIONS We can conclude from the present results that 13C NMR in conjuction with the CP-MAS

methods can be used to probe the interaction mechanism between the electron donor and the Ziegler-Natta catalyst at the natural 13C isotope abundance if a high enough loading level of the electron donor is used.

The structure and exact assignment of coordination sites of the silyl ether on the MgClz support is not unambigious on the basis of mere 13C CP-MAS NMR, where relatively small changes in the isotropic chemical shift for the coordinating methoxy group of the silyl ether species were observed on adsorption. A small change in the isotropic chemical shift does not necessarily reflect the real changes in the electronic environment of the methoxy group of RSi(0Me)S upon coordination, since the large opposing changes in the three components of the chemical shift tensor can cancel and result in a small change in the isotropic chemical shift lo).

These studies and the results of RSi(OMe)3 (R = Et or OMe) will be the subject of the forthcoming paper.9’

REFERENCES 1. P. Pino and R. Mulhaupt. Angew. Chem. Int. Ed. Engl., l2, 857 (1980).

2. J.C.W. Chien, J.C. Wu and C.I. Kuo, J. Polym. Sci. Polym. Chem. Ed., a, 2019 (1982).

3. S. Parodi, R. Nocci, U. Giannini. P.C. Barbe and U.Scata, Eur. Pat., 45975-45977.

4. a) Montedison SPA, Eur. Pat. Appl., 223 010 ; b) A. Monte and G. Cecchin, Eur. Pat. Appl., 29232 ; c) Nippon Oil KK, US. Pat., 4 619 981.

5. E. Whasarja, T.T. Pakkanen, T.A. Pakkanen, E. Iiskola and P. Sormunen, J. Polym. Sci. Polym. Chem. Ed., 2, 3241 (1987).

6. P. Sormunen, E. Iiskola, E. Vahbarja, T.T. Pakkanen and T.A. Pakkanen, J. Organomet. Chem., m, 327 (1987).

7. L. Cocco and D. P. Eyman, J. Organomet. Chem., D, I (1979).

8. C. E. Bronnimann and G. E. Maciel, J. Am. Chem. Soc.. U, 7154 (1986).

9. T.T. Pakkanen, E. Vahbarja, T.A. Pakkanen, E. Iiskola and P. Sormunen, submitted for publication

10. N.J. Clayden, S. Holmes and P.J.V. Jones, J. Chem. Soc. Chem. Commun., 1289 (1988).

144 P. Sonnunen, T. T. Pakkanen, E. Vihasarja and E. Iiskola

1

I i

* I

FIQUR8 2. 62.9 YE8 "C- ( 'a) MNR 8paattur of a I t 1 rixturr o f A l B t , an4 PhEi(ON.), in C6D6. ("C 8ign.18 OS irpurit im8 in A l E t , *)

11. Analysis of Sib1 Esters MI MgClz Supported Catalysts 145

150 I 4 0 110 I 2 0 110 100 90 80 20 60 50 40 30 20 LO 0 PPM

FIQURB 4. 62.9 H H r "C'CP-HA6 spectrum of tha Ph8i (ONm)s modiiiad NpCl,. ("C signals of delrin , Allt,(OBt) Qs

146 P. Sonnunen, T. T. Pakkanen, E. Vahasarja and E. Iiskola

~ I O U R B 5 . 62.s YES 13c CO-NAI mpaatrur or the roditiad H g C l , mupport a t t a r t h e T I C l , traatmant. ("C mignalm of d a l r i n )

. . . . . . . . . . . . . . . . . . . . . . . . . . I50 I40 I30 120 110 100 90 80 70 60 50 40 30 20 I0 0 -10

PPH

I I Q U R X 6 . 62.9 YES "C CO-UALI mpaotrur of thm MgCl,-mupportad o a t a l p s t a t t a r the A l x t , a a t i v a t i o n . tl'c mignalm ot dalr in *, haxana

147

12. Infrared Characterization of Supported Propylene Polymerization Catalysts - A Link to Catalyst Performance

Gregory G. Arzoumanidis and Nicholas M. Karayannis

Amoco Chemical Company P.O. Box 3011 Napenrille, Illinois 60566 United States of America

INTRODUCTION

Application of IR spectroscopy in supported olefin polymerization catalyst characterization has been rapidly increasing in recent years. 1-3 However, most of the work on propylene polymerization catalysts has focused on the spectra of the catalysts at 1800-1600 cm-1,1-3 i.e. , the vC-0 region of the internal modifier (mainly ethyl benzoate [EB] or dibutyl phthalate [ DBP] ) . ' polymerization catalysts, 4-6 we have used various regions of the IR spectrum, including the far-IR region, to determine the presence of undesirable contaminants in the final catalysts, arising from either use of insufficiently pure raw materials or temperature deviations during catalyst activation. characterization of supported polypropylene catalysts and its usefulness in predicting catalyst performance in some detail.

During research in these laboratories on supported propylene

The present communication describes our IR method of

EXPERIMENTAL

The catalysts studied, consisting of a titanium chloride-active species on a magnesium-containing support and including DBP as internal modifier, were prepared by employing standard procedures previously described. 4-6 IR spectra of the catalysts were recorded on Nujol mulls between NaCl or CsI windows over the range of 4000-200 cm-l using a Model 683 Perkin-Elmer recording spectrometer with an attached 3600 data station. The mulls were prepared in a dry, deoxygenated nitrogen atmosphere (drybox) by grinding the dry catalytic solid with an agate mortar and pestle and combining 50 mg of the solid with 5-6 drops of Nujol. The conclusions drawn from the IR evidence were compared to 2-hr batch slurry propylene polymerization evaluations of the catalysts with triethylaluminum-diphenyldimethoxysilane as cocatalyst and external modifier, respectively, (Al/Si/Ti molar ratio: 600/20/1) , performed as described elsewhere;4i7 and to catalyst analyses for Ti, Mg, C1, DBP and, in the case of samples with substantial phthaloyl dichloride (PDC) content, phthalic acid (PA), produced by hydrolysis of PDC .

148 G. G . Arzoumanidis and N. M. Karayannis


Properly activated and well-performing catalysts exhibit the following IR spectral features (Figures 1-3):

1. The uC-0 mode, occurring at ca. 1730 cm-' in free DBP, 3i4

appears as a very strong absorption at 1700-1685 cm-', arising from coordination of DBP to Mg, via the C-0 oxygen. Mg(I1) complexes with DBP show the uC-0 mode at 1688 cm-', whereas TiCl,-DBP complexes exhibit a uC-0 doublet at 1650 and 1584 The uC-0 band is relatively sharp with no significant shoulder at ca. 1650 cm-', due to Ti-DBP complexes and minimal absorption at 1900-1750 cm-', where PDC exhibits the uC-0 mode and various vibrational overtones and combination modes;'*' free PDC shows strong maxima at 1865, 1805, and 1785 cm-' in this region, as well as uC-C1 bands at 898 and 865 cm-'.'

In fact,

2. Three main uM-ligand bands at 460-370 cm-', appearing at 458- 454, 413-409, and 375-372 cm-', tentatively assigned as uMg-0 (C-0 of DBP) , lo uMg-Cl," and vTi-Cl (terminal C1) ," respectively.

3. Minimal absorption in the uOH (hydroxyl/water) regions, i.e., 3700-3200 cm-1.13*''

When during catalyst activation, which involves treatment of the support with TiC1, and DBP in a hydrocarbon or chlorocarbon diluent (e.g., toluene, chlorobenzene) , '-' the temperature of the mixture is significantly higher or lower than that prescribed (which is in the 120- 140°C range, depending on the particular type of catalyst being prepared) ,'-' catalysts exhibiting inferior performance (yields, boiling hexane extractables) relative to those properly activated are obtained. Overactivated catalysts (i.e., activated at temperatures higher than the optimum) show increasing levels of PDC, produced by chlorination of DBP with TiCl,, with increasing activation temperatures. spectrum of an overactivated catalyst is illustrated in Figure 4. uC-0 mode of PDC appears triply split with the strongest maximum at 1761- 1755 and relatively weaker maxima at ca. 1770 and 1753-1751 cm-'. 1900-1800 cm-', several bands also appear, including the strongest at 1864 with satellites at 1874 and 1853, a quartet with its center at ca. 1835 and very weak maxima at 1818, 1807, and 1798 cm-'. Figure 4) of overactivated catalysts at 460-370 cm-' do not appreciably differ from those of satisfactory catalysts, but those at 950-850 cm-' show increased absorbance due to the uC-Cl bands of PDC.' Since even underactivated catalysts contain some PDC, the effects of this contaminant on performance are estimated by the absorbance ratio of uC-0 at 1761- 1755/uC-0 at 1700-1685.

A typical IR The

At

Spectra (not shown in

This ratio is in the 0.1-0.3 range, and

12. IR Analpi of Suppwted Cutahst 149

occasionally as high as 0.35 in catalysts with satisfactory performance, but beyond this range activity decreases with increasing absorbance ratio.

Underactivated catalysts invariably contain significant amounts of TiC1, complexes with DBP, coprecipitated with the catalytic solid and resulting in an adverse effect on performance. shown in Figures 5 and 6. manifested by a maximum at 1650-1640 ~m-',~~' as well as by additional bands in the lower-frequency IR spectrum, as follows: at 435-430, whilst the intensity of the absorption at 413-409 becomes almost equal to that at 375-372 cm-' (see Figures 3 and 6). are most probably due to vTi-C1 (terminal C1) modes of bi- or poly-nuclear chloro-bridged TIC1,oDBP complexes. 15*16 In fact , whereas monomeric octahedral adducts of TiC1, exhibit the vTi-C1 band at ca. 375 cm-1,12i15 di- or pol -meric chloro-bridged complexes, such as TiC1,oEB or 2TICl4oEB,' and the Ti,Cl, anion, l6 reportedly exhibit strong uTi-C1 absorption bands at 435-405 ~rn-'.'~.~~ It should be noted that a 1:l TiC1,oDBP complex synthesized showed maxima at 406, 400, 383, and 374 cm-'.

The IR spectra of such catalysts are The presence of TiC1,oDBP complexes is

A new band appears

These bands

An illustrative example of the effects of proper activation versus over- or underactivation is given in Table I, which shows performance, IR, and analytical data for a series of catalysts produced by activating aliquots of the same support batch at various temperatures in the 115-135°C range. For this particular catalyst, the optimum activation temperature is between 120-125'C. Underactivation (115°C) results in lower yields and significantly increased DBP content, while slight overactivation (130°C) also leads to yield decreases, as well as reduced DBP content, Overactivation at 135°C leads to dramatic yield decrease, conversion of substantial amounts of DBP to PDC, and incorporation of 3-4 times more Ti in the catalyst. On the other hand, the Ti content steadily decreases as the activation temperature increases in the 115-130°C range. This is also reflected in the IR spectra of the corresponding catalysts, in which the vC-0 band at 1700-1685 cm-' becomes sharper with activation temperature increase, due to decrease of TiC1,oDBP complex (shoulder at 1650 cm-') content. Phthalic acid (PA) determinations for the catalysts activated at 115-130°C did not show the expected increase with increasing temperature, despite the obvious PDC content increase shown by the absorbance ratio of the two vC-0 bands. However, the catalyst activated at 135°C showed a PA analysis compatible with the IR ratio.

Occasionally, supported catalysts exhibiting uOH (hydroxyl) and uOH and 6HOH (water) bands have been produced, owing to use of support precursors contaminated with Mg-OH containing impurities and insufficiently dried starting materials (e.g., DBP). Catalysts of this t e show decreased activities and exhibit uOH (hydroxyl) at 3550-3520,"uOH (water) at ca. 3370, and 6HOH at ca. 1612 cm-' (Figure 7).14

150 G . G . Arzoumanidis and N. M. Karayannis

In conclusion, catalyst IR characterization is not only useful in detecting either employment of improper activation temperatures or use of contaminated starting materials in catalyst preparation, but also can provide fairly accurate predictions regarding catalyst performance in propylene polymerizations. Current IR studies are directed toward the identification of additional characteristic catalyst absorption bands, as well as characterization of intermediate products of catalyst preparation.

REFERENCES

1.

2.

3 .

4.

5.

6.

7.

8.

T. J. Burkhardt, A. W. Langer, D. Barist, W. G. Funk, T. Gaydos, in "Transition Metal Catalyzed Polymerizations. Ziegler-Natta and Metathesis Polymerizations," R. P. Quirk, Ed., Cambridge University Press, Cambridge, England, 1988, p 227.

E. Rytter, S. Kvisle, 0. Nirisen, M. Ystenes, H. A. Oye, ibid., p 292.

M. Terano, T. Kataoka, M. Hosaka, T. Keii, in "Transition Metals and Organometallics as Catalysts for Olefin Polymerization," W. Kaminsky and H. Sinn, Eds., Springer- Verlag, Berlin, 1988, p 55.

N. M. Karayannis, B. V. Johnson, C. R. Hoppin, H. M. Khelghatian, ibid., p 231; Makromol. Chem., in press.

G. G. Arzoumanidis, S. S. Lee (to Amoco Corporation), U.S. Patent 4,540,679 (1985); G. G. Arzoumanidis, H. M. Khelghatian, S. S . Lee (to Amoco Corporation), U.S. Patent 4,612,299 (1986); G. G. Arzoumanidis, N. M. Karayannis, H. M. Khelghatian, S. S. Lee, B. V. Johnson (to Amoco Corporation), U.S. Patent 4,866,022 (1989).

B. V. Johnson, N. M. Karayannis, C. R. Hoppin, L. Ornellas (to Standard Oil Company, Indiana), U.S. Patent 4,581,342 (1986); N. M. Karayannis, J. S. Skryantz, B. V. Johnson (to Amoco Corporation), U.S. Patent 4,657,882 (1987).

N. M. Karayannis, S. S. Lee, Makromol. Chem., m, 1171 (1982); 184, 2275 (1983).

H. N. Al-Jallo, M. G. Jahloom, Spectrochim. Acta, 288, 1665 (1972).

12. IR Analysis of Suppmted Cutulyst 151

9. C. Garrigou-Lagrange, N. Claverie, J.-M. Lebas, M.-L. Josien, J. Chim. Phys. Physicochim. Biol., x, 559 (1961); P. Delonne, V. Lorenzelli, A. Alemagna, ibid., a, 4 (1965).

10. E. C. Gruen, R. A. Plane, Inorg. Chem., 4 , 1123 (1967).

11. K. Handlir, J. Holecek, L. Benes, Coll. Czechosl. Chem. Commun., s, 2422 (1985).

12. R. J. H. Clark, W. Errington, J. Chem. SOC., 8 , 258 (1967).

13. R. T. Mara, G. B. B. M. Sutherland, J. Opt. SOC. her., 42, 1100 (1953); L. H. Jones, J. Chem. Phys., 2, 217 (1954).

14. I. Nakagawa, T. Shimanouchi, Spectrochim. Acta, a, 429 (1964) .

15. M. Ystenes, E. Rytter, Spectrosc. Lett . , a, 519 (1987). 16. R. J. H. Clark, M. A. Coles, J. Chem. SOC., Daltan Trans.,

2454 (1972).

152 G. G. Arzoumanidis and N. M. Karayannis

TABLE I

Effect of Supported Catalyst Activation Temperature pn Performance and ComDosition of th e Catalytic Sol ip

Activation TemDerat ure Slurrv Perf onnance 115°C 120°C 125°C 130°C 135°C

Yield g PP/g cat 12,400

Boiling Hexane Extractables, % 2.3

Catalyst Color Yellow

Catalvst Cornnosition.

Ti 3.3

Mg 14.3

c1 50.2

DBP 16.3

PA 0.2

Ratio uCO(PDC)/uCO(DBP) 0.04

20,800

2.3

Tan

3.2

14.8

51.8

10.4

0.4

0.10

15,200

2.2

Tan

2.7

15.5

52.1

10.3

0.2

0.14

11,200

2.1

Orange

2.4

15.4

50.3

7.1

0.2

0.28

6,900

7.5

Brown/ Orange

10.9

13.4

51.0

2.7

3.6

1.25

12. IR Analysis of Supported Catalyst 153

IR 5 We1

lpectra of Properly Activated and -Performing Catalysts

N pl ull,

2O00 1900

T 1 5 5 0 5

Fig. 1

le00 1700 1600

Fig. 2 1 1500 an-’

Fig. 3

1 an-’

IR Spectrum of Overactivated Catalyst

1800 1700 1600

Fig. 4

1 1500 crn-'

IR Spectrum of Underactivated Catalyst

2000 1900 I '0 Fig. 5 1'

+ VI P

IR Spectrum of Underactivated Catalyst n

e

Fig. 6

IR Spectrum of Contaminated Catalyst

4000 I 3000

1 Nujol +ll, NaCl n

2000 1500 1(

Fig. 7

K) crn-'

155

13. Microtacticity Distribution of Polypropylenes Prepared with MgC12 Supported Ti Catalyst Systems

Tatsuya Miyatake, Kooji Mizunuma, Masahiro Kakugo*

Chiba Research Laboratory, Sumitomo Chemical Co., Ltd., 2-1 Kitasode, Sodegaura-cho, Kimitsu-gun, Chiba 299-02, Japan

ABSTRACT The effect of phenyltrimethoxysilane as an external donor on

the microtacticity distribution of the isotactic parts of

polypropylenes prepared with MgC12-supported Ti catalyst-A1Et3 system was studied by programmed temperature column fractionation (PTCF)

technique. Both catalysts produce two kinds of isotactic polymers,

i.e., low isotactic and highly isotactic. The proportion of highly

isotactic polymer increases and the microtacticities of low and

highly isotactic polymers increase by the addition of the electron

donor. Models for active sites on the Mg-Ti catalyst system and the

action of PTMS to each active site are discussed based on these

results.

INTRODUCTION

In the polymerization of propylene with MgC12-supported Ti (Mg-Ti)

catalyst systems, electron donors used as internal and external donors play an important role in improving the stereospecificity of the catalyst systems. For example, the isotactic index (1.1.) of

polypropylene (i.e., the proportion of boiling heptane insoluble

fraction) prepared with Mg-Ti catalyst including ethyl benzoate as

internal donor (Mg-EB-Ti) catalyst-AlEt3 system is only 28% but when methyl p-toluate (MT) is added as external donor, the 1.I.X increases

to 88%.l) Moreover, the microtacticity of the isotactic part of

polypropylene, isotactic pentad (mmmm) fraction, is also improved by

the addition of MT.l) From the microtacticity distribution of the

isotactic part of the polypropylenes prepared with Mg-EB-Ti catalyst

with or without external donor, MT, determined by a programmed

temperature column fractionation (PTCF) technique, we showed that the

156 T. Miyatake, K. Mizunuma and M. Kakugo

highly isospecific active site is generated by the addition of MT and

proposed that a nonstereospecific active site is converted into a

highly isospecific active site.l)

Recently, some patents have shown that the combination of aromatic

diester and organosilicon compounds as internal and external donors

markedly improve the stereospecificity of the Mg-Ti catalyst system

(I.I.>95%). 2*3) In a previous paper,4) we reported that two

isospecific active sites are present in Mg-Ti catalyst including

diisobutyl phthalate (DBP) as an internal donor (Mg-DBP-Ti) catalyst -AlEt3 with or without external donor, phenyltrimethoxysilane (PTMS),

and that the stereoregulating ability of two active sites increase with the addition of PTMS.

In the present work we investigated the effect of individual

electron donors separately. The objective of the present study is

specifically to understand the effect of the external donor, PTMS,

using Mg-Ti catalyst free from internal donor. PTCF technique was

used to determine the microtacticity distribution. As a result, it

was found that two isospecific active sites differing in

stereoregulating ability are present in Mg-Ti catalyst systems, and

that PTMS plays two roles, i.e., 1) deactivation of nonstereospecific and low isospecific sites and 2) enhancement of the stereoregulating ability of highly isospecific sites.

EXPERIMENTAL Material s

Anhydrous MgC12, TiC14, and phenyltrimethoxysilane (PTMS) were purchased from Wako Pure Chemical Industries. Triethylaluminum (TEA)

was purchased from Toyo Stauffer Chemical. These materials were used

without purification. Catalyst preparation

Anhydrous MgC12 was dried at 300°C for 5h in vacuo. The dried

MgC12 (75 g) was put into a 250 ml stainless steel vessel containing

9 mm diameter steel balls (260 g), then ground on a vibrating mill

for 6h. TiC14 (200 ml) was introduced, and the grinding process was

continued for 4h. The resulting solid was transferred into a 100 ml

flask, washed seven times with heptane (20 ml), and dried in vacuo.

The Ti content of the solid catalyst was 0.43 wt%. These operations

were carried out under argon.

13. MicrofaCtiCiry Distribution of PP 157

Polymerization procedure

Polymerizations were carried out in an 1-L autoclave in heptane

(400 ml) at 70 "C. Hydrogen and propylene were fed into the

autoclave, and the mixture of solid catalyst, TEA, and PTMS

introduced. The polymerization was continued for lh, then stopped

by the addition of 2-methylpropanol. After the catalyst residue

was removed by extraction with 1N HCl/methanol solution, the product

was dried in vacuo. Detailed polymerization conditions are given in

Table 1.

Solvent extraction

The sample was completely dissolved in boiling xylene and the

solution was cooled gradually to 20°C. The precipitated polymer was

separated by filtration. The polymer soluble in xylene at 20°C was

recovered from the filtrate by evaporation. Further, the precipitated polymer was extracted with boiling heptane in a Soxhlet

extractor.

Elution column fractionation

Ten grams of the whole polymer was dissolved at 130 "C in xylene,

then 1200g of sea sand (35-48 mesh) kept at 130°C was put into the

solution. The mixture was cooled gradually 'to 20°C. By this

treatment, the higher isotactic polymer is deposited first and the

lower last to achieve satisfactory fractionation. Then the

mixture was put into a column (74 mm in diameter and 435 mm in height) immersed in an oil bath maintained at 20°C. The first

fraction was eluted at 20°C by dropping xylene into the column.

Five hundred ml of xylene was used to elute each fraction.

However, when a precipitate or milky turbidity appeared by the addition of the last several droplets of the eluate into methanol,

some additional xylene was introduced until the one or the other

disappeard. The time required was about 1 hr. Consecutive

fractions were obtained by raising the elution temperature stepwise

up to 130°C. The polymer fractions were precipitated by the addition of the eluates into 2.5 1 of methanol, recovered by

filtration and dried in vacuo. The fractions were obtained every 10" to 20°C in the region of 20"to 60"C, every 2"to 10°C in the region of

60" to 90 "C, every 1" to 2 "C in the region of 90" to 110°C. and every 0.5" to 1°C over 110°C. The elution temperature was controlled to

within fO.l"C. As a result, the number of fractions varied from 26


to 37, depending on the isotacticity of the samples. The

differential distribution curve was determined from the slope of the cumulative distribution.

Analytical procedure Melting temperature of the samples was measured on a Perkin Elmer

type-2 differential scanning calorimeter (DSC). The sample was pre- melted in DSC at 220 "C for 5 min. then rapidly cooled to room temperature. Thermogram was recorded by raising the temperature

from 40" to 180°C at a rate of 5 "C/min. I3C NMR spectrum was obtained at 135°C on a JEOL FX-100 pulsed Fourier transform NMR spectrometer. Experimental procedure and instrument conditions are described in a previous paper. Pentad tacticity was determined from the area of the resonance peaks of the methyl region. The

molecular weight distribution of the samples was determined with GPC (Waters Associates type 150C) in o-dichlorobenzene at 140°C. The intrinsic viscosity (IV) of the samples was measured in tetralin

at 135 "C.

Table 1. Results of propylene polymerization and solvent extract iona)

CataPys t Activity IVb) So 1 vent Micro- system extract ionc) tact ici tyd)

(g-PP/g-Ti. h) Atactic% Isotactic%

A Mg-Ti/AlEt3 21900 0.7 46.1 25.8 0.952

B Mg-Ti/AlEt3 7950 1.1 17.5 61.3 0.967

/PTMS~) a) Polymerization Conditions: 1-L autoclave; heptane, 0.4 1;

pressure, 6 kg/cm2G; HzI 3.3 ~01%; AlEt3, 1.8 mmol; polymerization temperature] 70°C; time, 1.0 h.

b, IV; Intrinsic viscosity measured in tetralin at 135°C. c, Atactic%; % fraction soluble in xylene at 20°C.

Isotactic%; % fraction insoluble in boiling n-heptane. d, Isotactic pentad (m) fraction of the fraction insoluble in

boiling n-heptane. e, PTMS; Phenyltrimethoxysilane. PTMS/Al; 0.15 mol/mol.

13. MicrotaCiiCity Distribution of PP 159

RESULTS

Table 1 shows the results of propylene polymerization by Mg-Ti catalyst-AlEt3 systems with or without PTMS, and the results of the solvent extraction of the polymers obtained. The addition of PTMS decreased the catalytic activity but increased isotacticity of the

polymer to a great extent. Moreover, the microtacticity of the isotactic part, i.e., mmrnm fraction, was improved by the addition of PTMS. These results are similar to the case of the Mg-DBP-Ti

catalyst-AlEt3 systems reported previ~usly.~,~) In order to understand the additive effect of PTMS, we have

investigated the detailed microtacticity distribution of these samples by PTCF technique. Figure 1 shows the cumulative and differential distribution curves in the region of the elution temperature of over lOO"C, and the melting temperatures of the fractions obtained. The melting temperature of the eluted polymer increases monotonically with increase in elution temperature due to the linear relationship between the melting temperature of the fractions and the mrnmm fraction. This indicats that fractionation takes place according to isotacticity. In the absence of PTMS two peaks of the differential curves are seen at the elution temperatures of 115"and 107°C. Similarly, two peaks are seen in the presence of PTMS, but the peaks are located at 119°C and 109"C, higher than those of the corresponding peaks in the absence of PTMS. This reflects increase of the mrnmm fraction. The molecular weight distribution (MWD) curves of the fractions were measured by GPC. The average molecular weight of the fraction increased with increase in the elution temperature and the values of Mw/Mn ranged from 1.9 to 2.4 in both samples.

From the differential fractionation curves and the MWD curves, bird's eye views of the isotactic parts are depicted in Figure 2 based on the mmmm fraction converted from the elution temperature. In the absence of PTMS, the microtacticity of the two peaks were 0.960 and e. 0.94, and in the presence of PTMS 0.973 and ca. 0.95. The microtacticity increased and the proportion of highly isotactic polymer to low isotactic polymer was estimated to have changed from 60140 to 75/25 by the addition of PTMS.

cd r

CU

MU

LATI

VE

(WT

%)

ME

LTIN

G T

EMPE

RA

TUR

E (“

C)

-L

-L

-L

Q)

-A 0

0

P

Q)

43

UI

0 0

0

0

0

I I

I I

I I

I 1

13. Mimtactici& Distribution of PP 161

[mmmm]=0.960 kw 4

1 PTMS

4

Figure 2. Bird's eye views of the isotactic parts of polypropylenes.

Catalyst systems: (A) MgC12-supported Ti catalyst-AlEt3;

(B) MgC12-supported Ti catalyst-AlEt3-phenyltrimethoxysilane.


DISCUSSION

Analogous to the active sites for Tic13 catalyst reportd

previously,’) three types of active sites, models 1, 2, and 3 shown in Figure 3, are assumed for Mg-Ti catalyst systems. According to

Arlman and C o s ~ e e , ~ , ~ ) the isospecific active site in the 6-Tic13

system consists of four C1 ions, an alkyl group, and a C1 vacancy,

and the nonstereospecific site three C1 ions, an alkyl group, and two

C1 vacancies. In the case of the Mg-Ti catalyst two types of isospecific sites can be assumed to be present on the surface of

MgC12 crystal similar to Tic13 catalyst. One consists of four

firmly bound C1 ions, an alkyl group, and a C1 vacancy (model 1) and the other two firmly bound C1 ions, two loosely bound C1 ions, an

alkyl group, and a C1 vacancy (model 2). The former isospecific

active site (model 1) appears to be structurally more rigid than the

latter active site (model 2) because the C1 ions are all bound to Ti atoms. The former active site will, therefore, possess stronger

isospecificity and the latter active site containing a loosely bound

C1 ion (model 2) will be attributed to the low isospecific site.

The active sites having two vacancies (model 3) probably become

nonstereospecific sites. Table 2 shows a comparison of relative activities of the

nonstereospecific, and low and highly isospecific sites in the absence and presence of PTMS. The addition of PTMS reduced the

activity of the nonstereospecific site to 1/10 and the activity of

the low isospecific site to 112, but influenced only slightly the

activity of the highly isospecific site.

CONCLUSION PTMS plays two roles, i.e., 1) deactivation of nonstereospecific

and low isospecific sites and 2) enhancement of stereoregulating ability of highly isospecific sites. This is different from the

case of MT, which produces highly isospecific sites anew.

13. Microkrcticily Distribution of PP 163

1. HIGHLY ISOSPECFlC

0 2. LOW ISOSPECFlC 3. NONSTEREOSPECFIC

Figure 3. Models &Jr the active sites in MgC,2-supported Ti

catalyst; (0) C1 vacancy.

Table 2. Relative activities of individual active sites in the absence and presence of PTMS

Active site Catalyst system Relative Mg-Ti/AlEt3 Mg-Ti/AlEt3/PTMS activity

( g-PP/g-Ti- h)

nons t ereos peci f ica) 1 ow is ospeci f icb) highly isospecificb) 4.9

10.1 3.3

1.4 1.5

4.4

0.1

0.5

0.9

a) Based on the fraction soluble in xylene at 20°C. b, Based on PTCF data.

REFERENCES

1. M. Kakugo, T. Miyatake, Y. Naito, and K. Mizunuma, Macromolecules,

2. Eur. Pat. 45977 (1981), Montedison S.p.a., invs.: S. Parodi, 21, 314 (1988).

R. Nocci, V. Giannini, P. C. Barbe, and V. Scata; Chem. Abstr. 96, 181808V (1982).

Y. Ushida, N. Kashiwa; Chem. Abstr. pp, 195588 (1983). 4 . M. Kakugo, T. Miyatake, Y. Naito, and K. Mizunuma, in: Transition

Metal Catalyzed Polymerizations, Ziegler-Natta and Metathesis Polymerizations; R. P. Quirk, Cambridge University Press: New York, New Rochelle, Melbourne, Sydney, 1988; p. 624.

5. E. J. Arlman and P. Cossee, J . Catal., 3 , 99 (1964). 6. E. J. Arlman, J. Catal., 5, 178 (1966).

3. Eur. Pat. 86288 (1983), Mitsui Petorochemical Industries, inv.:


165

14. Development of SiOa - Supported Type Catalyst for Propylene Polymerization

W.Hurata, A . N a k a n o , H . F u r u h a s h i a n d W.Imai

T o n e n S e k i y u k a g a k u K . K .

T o n e n C o r p o r a t e R e s e a r c h & D e v e l o p m e n t L a b o r a t o r y

I r u m a g u n , S a i t a m a . 354, J a p a n

1 . I n t r o d u c t i o n

H i g h a c t i v i t y , h i g h i s o t a c t i c i t y a n d g o o d p a r t i c l e m o r p h o l o g y

( s p h e r i c a l s h a p e a n d n a r r o w s i z e d i s t r i b u t i o n ) o f p o l y m e r p o w d e r a r e

r e q u i r e d t o a c h i e v e a s i m p l i f i e d p r o c e s s f o r p o l y p r o p y l e n e p r o d u c t i o n .

H i g h a c t i v i t y a n d h i g h i o s t a c t i c i t y o f p r o d u c e d p o l y m e r a r e

n e c e s s a r y t o a c h i e v e n o - d e a s h i n g p r o c e s s a n d n o - r e j e c t i o n p r o c e s s of

a t a c t i c p o l y p r o p y l e n e , r e s p e c t i v e l y . F o r t h e s e p u r p o s e s , Wg c o m p o u n d

s u p p o r t e d t y p e c a t a l y s t a r e u s e d w i t h e l e c t r o n d o n a t i v e c o m p o u n d s

(EDs). EDs a r e c o m m o n l y u s e d f o r b o t h c a t a l y s t p r e p a r a t i o n a n d

p o l y m e r i z a t i o n . G o o d p a r t i c l e s of p o l y m e r p o w d e r m a k e p o s s i b l e n o t

o n l y a n o - p e l l e t i z i n g p r o c e s s b u t a l s o t h e g a s - p h a s e p o l y m e r i z a t i o n

p r o c e s s w h i c h is c o n s i d e r e d t o b e t h e m o s t e c o n o i i c a l a m o n g v a r i o u s

p r o c e s s e s . P o l y m e r p o w d e r m o r p h o l o g y is g o v e r n e d by c a t a l y s t p o w d e r

m o r p h o l o g y , b e c a u s e t h e s e m o r p h o l o g i e s l o o k l i k e r e p l i c a .

So f a r S i O 2 - s u p p o r t e d c a t a l y s t s h a v e s h o w n l o w a c t i v i t y a n d l o w

i s o t a c t i c i t y in s p i t e of e x c e l l e n t p a r t i c l e m o r p h o l o g y b a s e d o n t h e

m o r p h o l o g y of S i O z p a r t i c l e i t s e l f . ' ) Ue a t T o n e n S e k i r u k a g a k u K.K. s u c c e e d e d in d e v e l o p i n g a S i O 2 - s u p p o r t e d t y p e c a t a l y s t w i t h h i g h

a c t i v i t y , h i g h i s o t a c t i c i t y a n d g o o d p a r t i c l e m o r p h o l o g y .

In t h i s p a p e r , t h e p e r f o r m a n c e o f o u r S i O 2 - s u p p o r t e d t y p e

c a t a l y s t will be i n t r o d u c e d a n d t h e r o l e of S i O 2 o n t h e p r o p e r t i e s o f

p o l y m e r i z a t i o n a c t i v e s i t e s will b e a l s o d i s c u s s e d .

166 M. Murata, A, Nakano, H. Furuhashi and M. Imai

2. Experiment

1 ) C a t a l y s t p r e p a r a t i o n - SiO2-Support e d C a t a l y s t (Cata1.A) P r e p a r a t i o n

S u p p o r t mat e r i a l v a s p r e p a r e d by t h e precipitation o f s p e c i f i c

M g c o m p o u n d on Si02. T h e c a t a l y s t v a s obtained by the t r e a t m e n t o f

support material vith Ti compound and E D s .

- Reference Ca t a l y s t (Cata1.B) P r e p a ration

Cata1.B vas p r e p a r e d by the s a m e p r o c e d u r e a s Cata1.A e x c e p t f o r

t h e absence of Si02.

2) Propylene polyme r i z a t i o n

- Propylene Bulk P o l y m e r i z a t i o n

Bulk polym e r i z a t i o n o f p r o p y l e n e v a s c o n d u c t e d at 70C. T h e

prescribed a m o u n t s of AIEt.3 and 3 r d - c o m ponents vere used a s the c o -

catalyst system. H 2 vas a l s o i n t r o d u ced a s t h e transfer reagent.

- Propylene Slu r r y P o l y m e r i z a t i o n

The slurry p o l y m e r i z a t i o n w a s c o nducted in n-heptane s o l v e n t by

t h e combination o f t h e c a t a l y s t a n d A l Et3 under 1 a t m p r e s s ure o f

propylene.

3) Determination of isotacticity ( 1 . 1 , ) o f polymer

1.1. value vas d e t e r m i n e d by 15 hrs extraction in boiling

n-heptane.

4) Measurement o f t h e n u m b e r of a c t i v e c e n t e r s

The numbers of a c t i v e c e n t e r s of both Cata1.A and Cata1.B v e r e

determined using t h e " s t o p p e d - f l o v " t e chnique, developed by Keii et

a1.,2' at 25T. BY the stopped- f l o v P o l y m e r i z a t i on vith Cata1.A. t h r e e phase

slurry, i.e., S i O 2 s o l i d c o n t a i n i n g vith polymer, EtOH/HCI s o l u t i o n

used a s quenching r e a g e n t a n d n - h e p t a n e o f polymerization solvent, vas

obtained. T h e p u r i f i c a t i o n of p o l y m e r v a s c a r r i e d o u t by t h e

folloving procedure. After r e m o v i n g EtOH/HCl solution, n-heptane vas

evaporated .

14. SO, Supported Cohzlyst fw PmpyCene P o l ~ t i o n 167

The solid (the mixture o f S i O z and polymer) was vashed with H 2 O

several times. In order t o d i s s o l v e the polymer, xylene v a s

introduced and r e f l u x e d f o r 1 hr under N 2 a t m o s p h e r e . T h e solution

was separated from S i O z s o l i d by hot filtration. T h e polymer v a s

obtained b y drying u p the x y l e n e solvent. The veight of polymer was

determined and t h e molecular veight vas measured by GPC. In addition,

t h e residual Si O z gel v a s c h e c k e d by I R . vhich d i d not c o n t a i n any

polymer.

5 ) Measurement b y X-ray P h o t o e l e c t r o n Spectroscopy(XPS)

Binding e n e r g i e s of Wgzs a n d T i ~ p o f Cata1.A a nd Cata1.B vere

determined b y XPS (Kratos. Exam 800). WgKa vas used a s t h e X-ray

source. The peak of C I S o f a seal t ape, by vhich catalyst powders

vere fixed on t h e s a m p l e cell. was used a s the s t a n d a r d f o r the

determination of the b i n d i n g energies.

3. Results and Discussion

3-1 Catalytic P e r f o r m a n c e of S i O z - S u p ported Catalyst (Cata1.A)

F i g . 1 . s h o v s t h e d e p e n d e n c e of p olymerization time on polymer

yield i n the c a s e of Cata1.A. P o l y m e rization v a s c o n d u c t e d in

propylene liquid at 70C. 15kg of polypropylene per l g o f c a t a l y s t

was produced in lhr of polymerization. This activity is equivalent

t o polymerizati o n using W g C l z - s u p p o r t e d type catalysts. T h e activity

durability during the c o u r s e of p o l y m e rization v a s excellent,

indicating that o p e r a t i o n control in a commercial Process may be easy.

F i g . 2 s h o v s the effec t of p o l y m e r ization t i m e o n isotacticity of

polymer vhich is produced under t h e s a m e polymerization c o n d i t i o n s a s

shorn in F i g . 1. T h e isotacticity vas constant at 97vtX. This may

indicate that Cata1.A can produce p o l y mers with uniform p r o p e r t i e s

independent of p o l y m e r i z a t i o n time.

168 M. Murata, A. Nakano. H. Furuhashi and M. Imai

4 0 0 0 0

$2 - 10000

0 1 2 3

T i m e ( h )

Fie.1 D e p e n d e n c e of polymerization t i m e on polymer

y i e l d with Cata1.A

P o l y m e r i z a t i o n C o n d i t i o n s ;

S y s t e m : C a t a l y s t / AlEt3 / 3rd-component / H z

p r o p y l e n e liquid, 70t

Fie.2 Effect of polymerization t i m e o n isotacticity

I s o t a c t i c i t y vas d e t e r m i n e d b y b o i l i n g

n - h e p t a n e e x t r a c t i o n f o r 15 hrs.

14. SiO, Supported Catahst for PrOpvCene Polyrneriuttimr 169

0 0

5 0

0

Particle s i z e d i s t r i b u t i o n s (PSDs) of Cata1.A and P o l y m e r

produced rith Cata1.A a r e s h o r n in Fig. 3. The PSD pattern o f Catal. A c o r r e s p o n d e d r i t h that o f Si02 itself, and the PSD pattern o f t h e polymer is equiv a l e n t t o t h a t o f t h e catalyst, a s s h o r n in Fig. 3.

F i g . 4 s h o v s S E l l p h o t o g r a p h s of Cata1.A a n d t h e produced polymer.

Both particles had s p h e r i c a l s h a p e s r ith smooth surface. These

resultsindicate t h a t t h e r e is a r e p l i ca relation of r o r p h o l o g i e s

betreen catalys t p a r t i c l e s and p o l y m e r particles.

, 1 , , a ,

Cata1.A

-

I , I . ,

1

x 2

c 4

3

.-

s

Fig.3

1 / p o l y " r

0 0

P a r t i c l e s i z e d istribution c u r v e s

As mentioned above,Catal.A s h o r s high activity, h i g h

isotacticity and e x c e l l e n t polymer p a rticle morphology. The

catalytic perfor m a n c e is good enough t o produce p o l y p r o p y l e n e in a

simplified process.

170 M

. Murata, A

. Nakano, H

. Furuhashi and M. Im

ai

C a t a l . A Polymer. o b t a i n e d w i t h C a t a 1 . A

F i g . 4 P a r t i c l e m o r p h o l o g i e s of S i O z s u p p o r t e d c a t a l y s t

a n d i t s p o l y m e r

14. Si02 Supported Cutolyst fw Propykne Polymerization 171

I I I 1

3 - 2 Investigat i o n of the R o l e of S i O z

F i g . 5 s h o w s the e f f e c t s of the concentration of AlEt3 (IAlEt31)

on isotacticities of p o l y m e r s produced rith Cata1.A and Cata1.B.

Propylene polym e r i z a t i o n s were c o n d u c ted by the s l u r r y polymerization

method without a n y third c o m p o n e n t or H z . In t h e c a s e o f both

catalysts, the i s o t a c t i c i t i e s g r a d u a l ly decreased with increasing

[AlEt31. The p o l y m e r isotacticity f or Cata1.A was higher t h a n that

for Cata1.B. T h e c o n t e n t of ED in Cata1.A was 2wtX. and t h e ED/Ti, E D / U g r a t i o s were 0.67(wt/wt) and 0.29(wt/wt), respectively. On the

other hand, the c o n t e n t o f E D in Cata1.B was lOrtX (ED/Ti 3.3(wt/

wtY) and ED/Ug = 0.50(wt/wt)). T h e s e r e s u l t s indicate t h a t Cata1.A

contains much lower E D than Catal.B, which is a u n i q u e c h a r a c t e r i s t i c

property of Cata1.A. From these results, it is c o n s i d e r e d that S i O z

affects the act i v e s i t e s to improve isotacticitu.

0

0- Catal.6

Fig.5 E f f e c t s of t h e concentration of AlEt3 on

isotacticity of polymers

Polym e r i z a t i o n C o n d i t ions ;

S y s t e m : Catalyst / AIEt3

n-heptane slurry p o l ymerization, 90min, 48C

Propylene pressure = 1 a t m

172 M. Murata, A. Nakano, H. Furuhashi and M. Imai

The result s o b t a i n e d by t h e s t o p ped f l o v p o l y m e r i z a t i o n vith

Cata1.A a r e summa r i z e d in Fig. 6. The p o l y m e r i z a t i o n s v e r e c a r r i e d

o u t in 100 mmol/l of AlEt3 c o n c e n t r a t i on at 25C. T h e d e p e n d e n c e o f

poludispersity, Zv/Wn, p o l y m e r y i e l d , Y , and t h e number-average

molecular veight, ~ n , on t h e p o l y m e r i z ation t i m e is discussed. T h e

values of flr/in a r e a l m o s t c o n s t a n t at 4. T h i s m e a n s that t h e n a t u r e

o f the active c e n t e r s is not c h a n g e d in e a c h polymerization. Y increased p r o port i o n a l l y vith time. in increased vith t i m e and

saturated to an intrinsic value. T h e n o n l i n e a r r e l a t i o n s h i p betveen

i n and t i m e s h o r s t h e o c c u r r e n c e o f c h ain t r a n s f e r reactions. T h e

r e s u l t s obtained f o r Cata1.B a r e a l s o s u m m a r i z e d in Fig. 7. S t o p p e d

f l o u polymerizat i o n c o n d i t i o n s a r e t h e s a m e a s t h o s e f o r Cata1.A.

Each result is s i m i l a r t o t h a t f o r Cata1.A. However, t h e wv/in value

of almost 5 for Cata1.B is different from that f o r Cata1.A (fiv/Wn = 4 ) .

These result s indicate t h a t t h e a c t i v e c e n t e r s o f Cata1.B a r e nore

heterogeneous t h a n t h o s e of Cata1.A.

Fig.6

2

1

c 'f P

R e s u l t s of "stopped flow" P o l y m e r i z a t i o n s

uith Cata1.A

P o l y m e r i z a t i o n C o n d i t i o n s ;

IAIEt3) = 100 m m 0 1 / 1 , 2 5 t

14. SiO, Supported Catalyst for Propvlene Polymerization 173

0 0.2 0.4 0.6 0. a

Poluwriutlon T i r e (S)

Fig.7 R e s u l t s o f "stopped flov" polymerizations

with the r e f f e r e n c e catalyst (Cata1.B)

P o l y m e r i z a t i o n C onditions ;

CAlEt31 = 100 m m 0 1 / 1 , 25C

The nurbe r of a c t i v e centers, [C"], and t h e propagation r a t e

constant, kp. v e r e d e t e r m i n e d by using t h e data o n polymer yield, Y, a n d t h e m o l e c u l e r veight, in. T h e r elationship betveen t h e nuaber-

average molecula r veight, a n d p o l y m e r yield, can expressed by equation

(1).

Wn = Y

42 x (1) [Cnl + S R t r dt

v h e r e [C'] a n i R t r s h o w t h e n u m b e r of active c e n t e r s at t i r e t a n d

transfer rate, r e s p e c t i v e l y . Y and S Rtr dt a r e expressed a s

fol lovs.

Y = kp[MI 5 [C'ldt

5 Rtr dt ktr (Ct)dt

(2) ( 3 )

174 M. Murata. A. Nakano, H. Furuhashi and M. Imai

w h e r e k p a n d k t r indicate t h e p r o p a g a t ion r a t e c o n s t a n t a n d t h e

transfer r a t e c o n s t a n t , r e s p e c t i v e l y . S u b s t i t u t i n g e q u a t i o n s (2) and

( 3 ) in equation (1) y i e l d s t h e f o l l o w i ng relation.

k t r

k ~ ( W 1

- Y/Wn = IC'I + * Y ( 4 )

- Equation ( 4 ) e x p r e s s e s t h e linear r e l a tion between Y/Mn a n d Y .

o n equation ( 4 ) . G o o d linear r e l a t i o n s between Y/in and Y a r e

o b t a i n e d for both Cata1.A a n d Cata1.B. B Y t h e e x t r a p o l a t i o n of t h e

lines to z e r o , t h e numb e r s o f a c t i v e c e n t e r s were d e t e r m i n e d a s 2.0 x

Fig. 8 s h o w s t h e " s t o p p e d f l o w P o l y m e r i z a t i o n r e s u l t s based

mol/mol-Ti f o r Cata1.A and 0.08 mol/mol-Ti f o r Cata1.B.

When the values o f [C'] a n d [ M I = 0.756 mol/l in equation(5). k p

v a l u e s a r e c a l c u l a t e d a s 990 (I/mol*s) a t Cata1.A and 2200 (l/mol*s)

at Catal.B, respectively.

0 20 40 60 80

Y Wmol-Ti)

Fig.8 R e l a t i o n s b e t w e e n Y/ln a n d Y

A s u m m a r y o f [C'l a n d k p is listed in T a b l e 1. SiO2-supported

catalyst (Cata1.A) has high [C*l v a l u e a n d low k p v a l u e s in c o m p a r i s o n

with the case o f Cata1.B. T h e d i f f e r e n c e s in k p values between Catal.

A and Cata1.B indicate c l e a r l y t h a t Si02 a f f e c t s the active s p e c i e s .

14. SiO, SupPored Gatulysi for Propvlene porvmCritation 175

Table 1 Surrarr o f k P a n d [C'l rvalurtlon

Cata I yst kP C0

(l/uol*s) (%-Ti)

Catal.6 2200 0.08

I n order t o clarify t h e cherical interaction of S i O z t o a c t i v e

species. X-ray p h o t o e l e c t r o n s p e c t r o s copy ( X P S ) r e a s u r r e n t s were also

carried out. XPS data is summ a r i z e d in Table 2. T h e binding

energies of M g z s a n d T i ~ p a t o m s w e r e d eterrined f o r both Cata1.A and

Cata1.B. The binding e n e r g y of Wgzs in Cata1.A was 90.7 (eV). On

the other hand, 90.4 (eV) was o b s e r v e d in Cata1.B. The d i f f e r e n c e s of

the two catalys t s in binding energy c an be regarded a s s i g n i f i c a n t ,

because the err o r of the value is commonly within 0.1 (eV). The

binding energie s of T i ~ p a t o m s a r e o b s erved b y a 0.3 (eV) s h i f t

between Cata1.A and Cata1.B.

T a b l e 2 XPS results

Binding Energy (eV)

Cata 1 yst M g z s T i 2 ~

Cata1.A

Cata1.B

90.7 459.0

9 0 . 4 458.7

The h i g h binding energy of T i ~ p in Cata1.A s h o w s the low electron

density o f Ti atom in corpar i s o n with Cata1.B. Soga et

demonstrated an e x c e l l e n t r e l a t i o n s h i p between t h e electron density of

Ti ator and k p value for metal c h l o r i de supported catalysts. T h e

h i g h electron density of a c t i v e Ti stabilizes t h e coordination o f

propylene uolecule with a c t i v e Ti due to t h e back-donation o f electron

fror active Ti to propylene monomer. That is to say, t h e high

electron density of a c t i v e Ti results in accelerated coordination o f

176 M. Murata, A. Nakano. H. Furuhashi and M. Imai

propylene into a t i t a n i u m - p o l y m e r c h a i n bond (increase of kp).

B a s e d on t h i s it c a n b e c o n c l u d e d that t h e lov electron density

o f Ti atom in Cata1.A g i v e s t h e lor k p value. T h i s is s u p p o r t e d by

t h e kP v a l u e s (see T a b l e 1 ) .

T h e s e X P S d a t a d i r e c t l y indicate that t h e electron e n v i r o n u e n t

in t h e a c t i v e cen t e r c a n be c h a n g e d b y t h e p r e s e n c e o f SiOz.

4. Conclusions

A h i g h p e r f o r m a n c e S i O 2 - s u p p o r t e d t y p e c a t a l y s t for propylene

From a n a l y s e s of t h e isotacticity o f polymer, t h e d e t e r m i n a t i o n

o f [ C ' ] a n d k p v a l u e s and X P S m e a s u r e u ent, it v a s c o n c l u d e d that Si02

is not a n inert s u p p o r t but a r e a c t i v e s u p p o r t vhich a f f e c t s a c t i v e

s p e c i e s t o c h a n g e c h e m i c a l properties.

polvrerization h a s been developed.

References

1 ) J P N . Kokai 54-148093. J P N . Kokai 5 6 - 9 8 2 0 6

2 ) T.Keii et al., Wakrouol.Chem., Rapid Commun.. 8, 583(1987).

3) K.Soga et al., K o u b u n s h i , 33, 682(1984) (in Japanese).

177

15. Effect of Silane Compounds on Catalyst Isospecificity-A Plausible Model Based on MO Calculation

T.OKAN0, K.CHIDA, H.PURUHASH1, A.NAKAN0, and S.ULKI Tonen Sekiyukagaku K . K . Tonen Corporate Research I Development Laboratory, Irumagun, Saitama, 354, Japan

INTRODUCTION Various k i n d s of e l e c t r o n donat ive compounds a r e commonly used f o r

The a d d i t i v e e f f e c t s of t h e e l e c t r o n donat ive compounds on propene polymerization t o achieve high i s o t a c t i c i t y of produced polymer.

i s o t a c t i c i t y have been i n v e s t i g a t e d . Tr i t t e t a1 . I ) demonstrated t h a t t he s t e r i c hindered amines gave h i g h i s o t a c t i c polymer w i t h both T i C 1 3 - and Mg-supported c a t a l y s t systems. Yano e t a1.2’ found t h a t the Uammt cons t an t s of t h e s u b s t i t u e n t s of p - s u b s t i t u t e d benzoates a r e r e l a t e d t o i s o t a c t i c i t y . These r e s u l t s i n d i c a t e t h a t t h e i s o t a c t i c i t y is a f f e c t e d b y both t h e s t e r i c a l f a c t o r and t h e e l e c t r o n i c f a c t o r of mod i f i e r s .

On t h e o the r hand, t h e r ecen t d i scovery of s i l a n e compounds i s e s p e c i a l l y noteworthy f o r t h e improvement of i s o t a c t i c i t y . The e f f e c t s of a lkoxys i l ane compounds on i s o t a c t i c i t y have been s t u d i e d f o r both T i c 1 3 - 3 1 and HgCln - supported type catalyst^,^. 5 , b u t un fo r tuna te ly , t he c o r r e l a t i o n between i s o t a c t i c i t y and t h e t y p e of s i l a n e compound has no t been made c l e a r .

The ob jec t of t h i s s t u d y is t o demonstrate the e f f e c t of s t r u c t u r a l a n d e l e c t r o n i c f a c t o r s of a lkoxys i l ane compounds on the a c t i v i t y and i s o t a c t i c i t y of propene polymer iza t ion . The volume of the

a lkoxys i l ane compound is cons idered a s t h e s t r u c t u r a l f a c t o r , and t h e e l e c t r o n dens i ty of oxygen atom i n alkoxy group is assumed a s the e l e c t r o n i c f a c t o r s i n c e t h e a lkoxys i l ane compounds i n t e r a c t w i t h T i i n t he c a t a l y s t a t t h e oxygen atom.5’ For q u a n t i t a t i v e a n a l y s i s , the volume and e l e c t r o n dens i ty a r e determined b y molecular o r b i t a l (MO) c a l c u l a t i o n s .

In this s t u d y , t h e S i02 - suppor t ed c a t a l y s t developed b y Tonen Sekiyukagaku K . K . i s used f o r t h e eva lua t ion of t h e a d d i t i v e

178 T. Okano, K. Chida. H. Furuhashi, A. Nakano and S. Ueki

e f f e c t s of a lkoxys i l ane compounds on i s o t a c t i c i t y .

EXPERINENTS and CALCULATIONS Si02-suppor ted c a t a l y s t p r e p a r a t i o n . Support n a t e r i a l was

prepared by the p r e c i p i t a t i o n of s p e c i f i c Hr compound on SiOo. The c a t a l y s t was obta ined by the t r ea tmen t of suppor t m a t e r i a l w i t h T i compound and ED.

Propene s lur ry po lvmer i za t io n . The slurry poymerization was conducted i n cyclohexane s o l v e n t b y s y s t e m c o n s i s t i n g of t h e c a t a l y s t , A l E t 3 , and i n d i v i d u a l s i l a n e compounds.

t i n e was 90 n inu te s . Propene p res su re was 1 atm.

polymer is represented by t h e weight f r a c t i o n of polymer residues i n b o i l i n g n-heptane e x t r a c t i o n f o r 15 hours (1.1.). I s o t a c t i c polymerization r a t e (Rp,!pp) and a t a c t i c po lymer iza t ion r a t e (Rplapp) were d e t e r i i n e d from t h e va lue of 1.1. and t h e whole polymer iza t ion r a t e (Rp) b y the fo l lowing equa t ions .

The polymer iza t ion t e n p e r a t u r e was 4 8 C , and t h e polymer iza t ion

Determination of i s o t a c t i c i t y of p o l y r e r . The i s o t a c t i c i t y of

Ca lcu la t ion of volume of s i l a n e compound molecule and e l e c t r o n d e n s i t y on oxigen atom. The e l e c t r o n d e n s i t y on the oxygen atom of a s i l a n e compound is obta ined b y N N D O (Modified Neglect of D ia ton ic Overlap) procedure,6.’1which is a v a i l a b l e f o r u s i n g NOPAC (QCPE # 4 5 5 ) * ’ . SCP convergence and energy minimization c r i t e r i o n were l i m i t e d to t h e program d e f a u l t va lues . The volume of t h e s i l a n e compound is eva lua ted from the volume of t h e s u m of t h e van de r Uaals r a d i i of t h e a tomsg’of s i l a n e compounds.

RESULTS and DISCUSSION The r e l a t i o n s h i p between t h e polymer iza t ion r a t e and t h e

concen t r a t ion of A 1 E t 3 , [ A l E t 3 3 was i n v e s t i g a t e d u s i n g S i02 - suppor t ed c a t a l y s t . The polymer iza t ion r a t e i n c r e a s e s g radua l ly w i t h i n c r e a s i n g [ A l E t 3 1 t o reach t h e cons t an t va lue . Based on this resul t , t h e subsequent polymerization e x p e r i n e n t s were c a r r i e d out a t t h e c o n s t a n t

15. Effect of Sihne Cumpounds on the Cotahst Isospecifin’ty 179

[ A l E t 3 1, 100 mmol/l, given t h e cons t an t po lymer iza t ion r a t e . Table 1 summarizes t h e r e s u l t s of propene polymer iza t ions w i t h

S iOp -supported type c a t a l y s t / A l E t 3 / d i a l k y l d i r e t h o x y s i l a n e c a t a l y s t s y s t e m . The c a t a l y t i c a c t i v i t y and t h e i s o t a c t i c i t y of produced polymer a r e shown i n Table 1 . The i n t r i n s i c va lues of t h e a c t i v i t i e s and i s o t a c t i c i t i e s seem t o depend on t h e type of s i l a n e compound. These r e s u l t s i n d i c a t e t h a t t he s i l a n e compounds a f f e c t t h e c a t a l y t i c p r o p e r t i e s of SiOe-supported c a t a l y s t as well a s TiC13-type and MgCl2-

supported c a t a l y s t s .

Table 1. The effect of various dialkyldiiethoxysi lane on polymerization rate of propene and isotacticity of produced PP” .

Dia 1 ky 1 - Rp 1.1. Run.Ho dilethoxysl lane e-PP/e-cab 1. hr X

1 (CH3)2Si (OCHd 2 22.2 84.3

2

3

4

49.3

30.3

96.3

94.5

7 97.3

8 0 2 - 0 SI(OCH3)a 54.5 90.4

.’ Catalyst system: SiOe-supported catalyst / AI(C*Hs), / dialkyl- dimethoxysilane Polymerization conditions: Cyclohexane slurry, 48’C, 1.5hr Concentration o f dialkyldiiethoxysilanc = lOmiol/l

In order t o c h a r a c t e r i z e t h e s i l a n e compounds, molecular o r b i t a l (no) c a l c u l a t i o n was conducted f o r each compound. The volume of s i l a n e compound and t h e e l e c t r o n dens i ty on t h e oxygen atom i n t h e alkoxy group w h i c h a r e determined from HO c a l c u l a t i o n s a r e summarized

180 T. Okano, K. Chida, H. Furuhashi, A. Nakano and S. Ueki

i n Table 2. Both the volume and the e l e c t r o n d e n s i t y i n each s i l a n e compound have c h a r a c t e r i s t i c va lues . The a c t i v i t i e s of i s o t a c t i c po lymer iza t ion , R P , I P P , and a t a c t i c po lymer iza t ion , R ~ , ~ p p , a r e a l s o shown i n Table 2 .

P i g . 1 shows a good r e l a t i o n s h i p between t h e volume of s i l a n e compounds and R P , I P P . the va lue of R P , I P P i n c r e a s e s w i t h t h e i n c r e a s e o f t h e volume. T h i s i n d i c a t e s t h a t R p , ~ p p depends on t h e s i z e of t h e s i l a n e compound i n propene polymer iza t ion . On t h e o t h e r hand, no c l e a r r e l a t i o n s h i p between the e l e c t r o n dens i ty of oxygen atom and R P , , ~ ~ is observed (P ig . 2 ) .

WKUME A'

P i g . 1

F i g . 1 Dependence o f i s o t a c t i c p o l y m e r i z a t i o n r a t e on voluue o f s i l a n e

coapound a o l e c u l e s .

F i g . 2 l s o t a c t i c p o l y u e r i z a t i o n r a t e vs. e l e c t r o n d e n s i t y o f oxygen atom o f s i lane coapounds.

R p , n p p is p l o t t e d a g a i n s t t h e e l e c t r o n d e n s i t y of oxygen atom i n P i g . 3 . R P , A P P decreased d r a m a t i c a l l y w i t h e l e c t r o n d e n s i t y . However, R P , ~ P P is not r e l a t e d t o volume of s i l a n e compound ( see F i g . 4 ) .

completely d i f f e r e n t f a c t o r s of s i l a n s compouds. R P , ~ P P changes w i t h volume of s i l a n e compound. On t h e o t h e r hand, R p , n p p is de te rn ined by

t h e e l e c t r o n dens i ty of t h e oxygen atom i n s i l a n e compounds.

These r e s u l t s s t r o n g l y i n d i c a t e t h a t R p , ~ p p and R P , ~ P P depend on

T a b l e 2. R e s u l t s o f MNDO c a l c u l a t i o n and i s o t a c t i c p o l y m e r i z a t r i o n r a t e ( R P , , ~ ~ ) and a t a c t i c p o l y m e r i z a t i o n r a t e ( R P , ~ ~ ~ )

RP. APP Di a 1 ky 1 - Volume Electron Density "RP. I P P a)

Run No. dimethoxysi lane x3 b)a.u. g-PP/g-cata 1. hr g-PP/g-catal . hr

120.1

154.0

171.0

175.5

205.2

222.1

222.4

231.2

0.6802

0.6874

0.7092

0.6933

0.6857

0.6892

0.7300

0.6989

18.7

41.6

47.5

34.3

45.8

51.5

57.0

52.5

3.5

2.9

1.8

2.0

4.2

2.5

1.6

2.0 B P

a) Rp. I P P = Rp x I.I./lOO , R P . A P P = RP x (1 - I.I./100 b, a.u.= atomic unit

182 T. Okano, K. Chida, H. Funhashi, A. Nakano and S. Ueki

0 -

1.0 I a61) am am a71 an a73

UEtTROn DEm /. O.U.

Pig.3 VOUM / A'

P i g . 4

F i g . 3 Dependence o f atactic polymerization rate on electron density o f oxygen atom o f silane compounds.

P i g . 4 A t a c t i c po lymer iza t ion r a t e v s . volume of s i l a n e compound molecules.

CONCLUSION

a c t i v i t y and i s o t a c t i c i t y were s t u d i e d w i t h S i02-suppor ted c a t a l y s t . Both a c t i v i t y and i s o t a c t i c i t y change w i t h t h e t y p e of s i l a n e compound.

The a p p l i c a t i o n of molecular o r b i t a l c a l c u l a t i o n t o t h e s i l a n e compounds make p o s s i b l e q u a n t i t a t i v e a n a l y s i s of changes i n a c t i v i t i e s and i s o t a c t i c i t i e s . I s o t a c t i c po lymer iza t ion ra te depends on t h e volume o f s i l a n e compound while t h e a t a c t i c po lymer iza t ion r a t e i s r e l a t e d t o the e l e c t r o n d e n s i t y of t h e oxygen atom i n s i l a n e compounds.

The a d d i t i v e e f f e c t s of d i a lky ld ime thoxys i l ane coipounds on both

P r o i t h e s e r e s u l t s , i t is concluded t h a t the c h e i i c a l p r o p e r t i e s of i s o s p e c i f i c s i tes a r e q u i t e d i f f e r e n t from those of n o n - s p e c i f i c s i tes , i . e . t h e r e e x i s t s he t e rogene i ty of a c t i v e s i t e s i n s o l i d c a t a l y s t s .

15. Effect of Sihne Compounds on the Catalyst Isospectfictty 183

Reference

1) I.Tritto, M.C.Sacchi, P.Locatelli, and G.Zannoni ; Hacromolecules, - 21, 384-387 (1988)

2) T.Yano, T.Inoue, S.Ikai, Y.Kai, M.Taaura, and H.Shimizu ; Eur

3) N.M.Karayannis, S.S.Lee, and D.J.Mangan ; J .Appl.Polym.Sci.,

Polym.J., 2-2, 637-641 (1986)

1329-1333 (1987)

4 ) K.Soga, T.Siono, and Y.Doi ; Makromol. Chem., 189, 1531-1541

- 9 34

1988)

5) K.Soga and T.Siono ; in "Transition Nethod Catalyzed Polymerizations, Ziegler-Natta and Metathesis Polymerizations " R.P.Quirk, Ed.,

Cambridge University Press, 1988, p,266 6) M.J.S.Dewar and W.Thiel ; J.Am. Chem. SOC., 99, 4899-4907 (1977) 7) M.J.S.Dewar, H.L.McKee, and H.S.Rzepa ; J.Am.Chem.Soc., 100, 3607

8) MOPAC,QCPE 1455 ( V A X version) :A General Molecular Orbital Package,

9) A.Bondi ; J. Phys. Chem., @, 441-451 (1964)

(1978)

Quantum Chemistry Program Exchange, Indiana University


185

16. 13C NMR Investigation on Lewis Base Activation Effect in High Yield Supported Ziegler-Natta Catalysts

Maria Carmela Sacchi, Incoronata Tritto, Chengji Shan Istituto di Chimica delle Macromolecole del CNR Via E. Bassini 15/A - 20133 Milano Italy

Lucian0 Noristi Himont Centro Ricerche Giulio Natta Piazzale Donegani 12 - 44100 Ferrara Italy

ABSTRACT

In this paper we will approach the study of the machanism of

the Lewis base activation in high yield supported Ziegler-Natta

catalysts by three different experimental routes: i) stereo-

chemical study, by 13C NMR analysis, of samples of polypropene

prepared using selectively 13C enriched AlEt3 as cocatalyst; ii)

GPC characterization of the most isotactic fractions; iii) study

of the exchange between internal and external base6 by GC

analysis of the base content of the solid catalyst. Despite the

well known complexity of the problem, on the basis of all these

data it is possible to single out some general trends of the

Lewis base activation and these trends depend more on the

characteristics of the specific pair of internal and external

bases than on those of the single internal or external base.

186 M. C. Sacchi, I. Tritto, C. Shan and L. Noristi

INTRODUCTION

In previous papers we reported a study of the mechanism of

the Lewis base activation in high yield supported Ziegler-Natta

catalysts for isotactic propene polymerizationl.2. It is well

known that the Lewis bases exert at least two different and

concurrent effects: i) poisoning of both isotactic and atactic

sites; ii) activation of the isotactic ones. A dominating

poisoning or activation is observed depending on the

polymerization Our approach consisted in finding

the conditions in which various Lewis bases, used both as

internal and external bases, produced a prevailing activation

effect. In such conditions we studied the effect of the Lewis

bases on the steric structure of isospecific centers of different

catalytic systems. The method we used to obtain structural

information on the active centers was the investigation, by 13C

NMR, of the initiation step in propene polymerization in the

presence of the selectively 13C-enriched cocatalyst

A1(13CHzCH3)3. Indeed, taking into account only monomer insertion

on the isotactic-specific centers, when polymerization starts on

a selectively enriched titanium-l'CHzCHs bond it is possible to

detect and distinguish the two possible stereoisomers of chain

end groupsa#g:

erythro threo

Erythro (or isotactic) is the stereoisomer in which the two

16. NMR Investigation on hi Base Actioation Effed 187

first monomeric units have the same configuration and threo (or

syndiotactic) that one in which they have the opposite

configuration. If e and t are the integrated peak areas of the

enriched methylene resonances assigned respectively to the

erithro and threo placements of the first propene unit, the e/t

ratio represents the extent of the first step stereoregularity.

We observed that the increase of the isotactic productivity due

to the presence of either the internal or the external bases, is

accompanied by a change in the extent of the first step

stereospecificity. On the basis of these findings and of our

previous data concerning conventional Ziegler-Natta catalystslo-12

we deduced that both the internal and the external bases are

present in the environment of at least some of the isospecific

centers and consequently the activation derives, at least

partially from a direct effect of the Lewis bases on the active

sites. In this paper some insights arrived at thorough different

experimental investigations will be summarized and we will

individuate some new aspects of the base activation effect

concerning the behaviour of the specific pairs of internal and

external bases rather than the behaviour of the single internal

or external base. In spite of the well known complexity of the

problem an attempt will be made to find out about some general

trends in the Lewis base behaviour.


1) Propylene polymerization in the absence of external base.

Propylene was polymerized with MgClz/TiClr, HgClz/EB/TiClr and

188 M. C. Sacchi. I. Tritto. C. Shan and L. Noristi

MgC12/DEHP/TiC14 catalytic systems (EB=ethyl benzoate, DEHP=di(2-

ethylhexyl)phthalate), using selectively 13C enriched AlEts as

cocatalyst. All the polymers were separated into isotactic and

atactic fractions by extracting them with boiling heptane. The

isotactic fractions were further extracted with boiling octane.

The heptane insoluble-octane soluble and octane insoluble

fractions of all the samples were characterized by gel permeation

chromatography and 13C NMR analysis. The polymerization

conditions and the results obtained are reported in Tab.1. The

polymerizations in the absence of the internal base were

performed with two differently prepared MgClz supports (runs 1

and 2). The polymerization with the catalyst containing EB (run

3 ) was repeated under different conditions (run 4 ) . In fact when

the catalysts containing an internal base are placed in contact

with AlEt3, they progressively lose the internal base and the

extent of this base extraction depends heavely on the time, the

aluminum/titanium ratio and the temperatures. Therefore, in order

to analyze the catalyst's behaviour in the conditions in which

the internal base should be at least partially present on the

solid catalyst, we repeated the polymerization 3 in milder

COnditiOn6, that 1s at lower time and temperature. In Tab.1 the

isotactic productivities of all the samples are shown. However a

correct evaluation of the increase of isotactic productivity due

to the presence of the internal bases is not possible in this

case since the samples are performed with catalysts containing

different amounts of fixed titanium (see note 12) observe that

with the catalysts that do not contain any base the isotactic

heptane insoluble fraction is nearly completely octane soluble

Table I EFFECT OF DIFFERENT INTERNAL BASES ON MgC1z SUPPORTED CATALYSTS

Catalyst

MgClz/TiClr

MgClz/TlClr

MgCl2/EB/TiClr

HgCl2/EB/TiClr

Ti% Y

0.34 22

2.43 50

1.33 65

1.33 31

MgClz/DEHP/TiClr 3.04 62

1.1.

49

41

45

72

73

I.P.

3170

843

2199

1678

1489

S-8 42

1-8 7

S-8 41

1-8 0

S-8 45

1-8 0

S-8 60

1-8 12

S-8 49

1-8 24

216

489

192

-

200

-

398

623

250

497

3.9

2.6

4.0

-

4.7

-

4.9

3.0

4.5

3.0

[mml

0.95

0.98

0.95

-

0.95

-

0.93

0.97

0.94

0.95

Cocatalyst: A1(13CH2CH3)3; Y: yield in grams of polymer/grams of catalyst-hour 1.1.: isotacticity index=weight percent of heptane insoluble fraction I.P.: isotactic productivity=grams of isotactic polymer/grams of Ti-hour S-8: octane soluble fraction; 1-8: octane insoluble fraction [mml: molar fraction of isotactic triads by NMR; e/t: intensity ratio of resonances related to the isotactic (e) and syndiotactic (t) placement of the first propene unit 8 : T=room temperature, time=l hr; b: T=O ‘C; t=30’ c : see note 13

e/tc

1.7

-9 -J

2.1

-

3.9

-

4.5

y8

2.0

“5


(run 2 ) and is characterized by a relatively low 'Hw. A small

octane insoluble fraction is present in run 1 (MgClz activated by

milling), and is characterized by higher g w and lower Ew/h

value. A greater octane insoluble fraction is obtained with the

catalyst containing DEHP as an internal base (run 5 ) . As to the

catalyst containing EB as an internal base, an octane insoluble

fraction is obtained only in the conditions in which the base is

less easily removed from the solid surface (run 4 ) .

The NMR data show that all the octane insoluble fractions have a

higher stereoregularity of both propagation and initiation with

respect to the octane soluble ones.

All these data suggest that EB is present in the environment of

the active titanium and its presence makes the isotactic sites

able to produce more stereoregular polypropene, characterized by

higher z w and lower Rw/Rn value. Indeed only this assumption

accounts for: i) the fact that only in mild polymerization

conditions (that is only when the base is maintained on the

catalyst surface) the octane insoluble fraction is present; ii)

the fact that in the octane insoluble fraction so obtained, the

e/t ratio is higher than in the octane soluble one. As to the

catalyst containing DEHP as an internal base (run 5 ) , the fact

that a noticeable octane insoluble fraction is already present at

standard polymerization conditions can be in principle accounted

for by two hypotheses: i) the diesters can be less easily removed

from the catalyst by AlEt313; ii) the removal of DEHP leaves

active sites characterized by higher isospecificity and/or higher

stability with respect to the catalyst without any base. The fact

that a small octane insoluble fraction is present even in the

16. NMR Investi&~tion on h i s Base Activation Effect 191

absence of internal base (run 1) shows that this kind of active

sites (which are characterized by high iw, low iw/Mn value and

noticeable first step stereoregularity) may be present, on the

catalyst surface, even without any base.

2 ) Propylene polymerization with different pairs of internal and

external bases.

Be

0

EB

Table I1

Y

65

38

TMPip 69

PTES 46

1.1

45

94

91

94

EFFECT OF DIFFERENT BASES ON THE CATALYST

I.P.

2199

2685

4721

3251

MgClz/EB/TiClr

Wt%

E-8 45

1-8 0

S-8 40

1-8 5 4

5-8 41

1-8 50

S-8 47

1-8 47

- MW. 10- 3

200

-

218

491

207

531

323

573

Rwlk [mml

4.7 0.95

- -

5.7 0,96

2.9 0.99

4.5 0.96

3.2 0.99

5.5 0.96

2.9 0.99

eltc

3.9

-

4 . 0

y7

2.8

‘10

5.4

“/lo

Cocatalyst: A1(13CH2CH,), Be: external base Y: yield in grams of polymerlgrams of catalyst*hour 1.1.: isotacticity index=weight percent of heptane insoluble

I.P.: isotactic productivity=yield in grams of isotactic

S-8: octane soluble fraction; 1-8: octane insoluble fraction [mml: molar fraction of isotactic triads by NMR elt: intensity ratio of resonances related to the isotactic (e)

c : see note 13

fraction

polymer/grams of Tiehour

and syndiotactic (t) placement of the first propene unit


Three different bases, EB, TMPip (2,2,6,6-tetramethylpiperi-

dine) and PTES (phenyltriethoxysilane) have been used with both

catalysts containing EB and DEHP respectively as internal bases.

All the results are shown in Tab.11 (EB as an internal base) and

Tab.111 (DEHP as an internal base). Some similarities and some

differences between the two series of experiments can be

recognized.

Table I11 EFFECT OF DIFFERENT BASES ON THE CATALYST

MgClz/DEHP/TiClr

Be Y

0 62

EB 75

TMPip 66

PTES 65

1.1. I.P.

73 1489

76 1875

91 1976

94 2010

Wt%

S-8 49

R-8 24

S-8 66

1-8 10

S-8 47

1-8 44

S-8 45

1-8 49

- MU-10-3

250

497

195

449

260

493

238

467

- Mw/i?n [mml

4.5 0.94

3.0 0.95

3.5 0.93

2 . 8 0.98

4.4 0.92

2.9 0.96

4.9 0.97

2.8 0.96

e/tc

2.0

55

2.2

%5

1.7

4.4

3.0

??a

Cocatalyst: Al(?’CH2CH,), Be: external base Y: yield in grams of polymer/grams of catalyst-hour 1.1.: isotacticity index=weight percent of heptane insoluble

I.P.: isotactic productivity=yield in grams of isotactic

S-8: octane soluble fraction; 1-8: octane insoluble fraction [mm]: molar fraction of isotactic triads by NMR e/t: intensity ratio of resonances related to the isotactic (e)

c : see note 13

fraction

polymer/grams of Tiohour

and syndiotactic (t) placement of the first propene unit

16. NMR Investigufirm on h i s Base Activofirm Effect 193

As to the former, if we take the experiments without any

external base as starting points, we can observe that the

addition of the external base always produces an increase of the

isotactic productivity, even if to a different extent depending

on the base. Moreover, when the external base is added, an octane

insoluble fraction is always present, and this can reach more

than 50% of the overall isotactic polymer and is characterized

by higher Mw and lower iiw/in value with respect to the

corresponding octane soluble fractions. However the behaviour of

every base with the two different solid catalysts is not the

same: e.g. the greatest improvement of isotactic productivity is

produced by TMPip with the catalyst containing EB and by PTES

with the catalyst containing DEHP; moreover EB is a relatively

efficient isotacticity improver with the former and an

inefficient one with the latter. The NMR data show that the [mml

contents are higher in the series of experiments with EB as an

internal base than in that with DEHP. All the e/t ratios of the

octane insoluble fractions are higher than those of the

corresponding octane soluble ones. It is interesting to observe

that all these e/t values are widely different from each other

and depend both on the characteristcs of the external base, as we

have already shownl, and on those of the specific combination of

external and internal base. In particular, with EB as an internal

base, both TMPip and PTES produce catalytic sites having an

initiation stereoregularity nearly as high as the propagation

stereoregularity while different and lower e/t values are

observed when the same two base8 are used with DEHP as an

internal base.

-


As to the octane soluble fractions, they are roughly

characterized the

[mml are slightly lower than in the corresponding octane

insoluble fractions. The e/t values are different and mostly

higher than those of the octane soluble fractions of the

corresponding catalysts without external base. It seems likely

that these fractions are produced by a mixture of active sites of

different kinds containing and not containing the internal and/or

the external base. The fact that TMPip produces a decrease of the

e/t values of the octane soluble fractions of both catalysts is

not easy to be accounted for.

by relatively low fiw and high fiw/Mn value and

3) Study of the interactions between the solid catalysts and the

external bases.

In order to get a better understanding of the activation

mechanism we have compared the above stereochemical data with the

results coming from a study of the exchange of components that

takes place between the solid catalyst and the cocatalyst

solution. It is known that when the solid catalyst is placed in

contact with a solution containing both AlEt3 and an external

base a partial replacement of the internal base by the external

one occurs.’ Table IV shows the results obtained by determining

the base content of both MgClz/EB/TiClr and MgClz/DIBP/TiCl4

catalysts after treatment with AlEt3 or AlEta/external base

mixtures. The contact conditions were chosen as close as possible

to the polymerization conditions. The contact procedure is

described in the Experimental Part. Methyl-para-toluate (MPT) was

16. NMR Investigation on Lewis Base Activation Effect 195

used instead of ethyl benzoate as an external base to make it

possible to recognize the internal-external base exchange when EB

is the internal base. The use of a catalyst containing di-

isobutyl phtalate (DIBP) as an internal base instead of DEHP

should not change the results, since it is likely that both

diesters have similar behaviour. The data of Table IV show that

the diester can be removed from the catalyst by this treatment to

a higher extent than EB, either with and without external base.

Table IV BASE CONTENT OF THE CATALYSTS TREATED WITH AlEtj/EXTERNAL BASE MIXTURES

Catalyst Treatment Base Content

MgClz/EB/TiClr (Ti = 1.7 % )

MgClz/DIBP/TiClr (Ti = 2 . 4 % )

Contact with In terna 1 mmol/lOOg

None 58

AlEt:, 10

AlEts/MPT (3/1) 27

AlEt 3 /PTES I' 18

AlEt 3 /TMPip " 15

None 44

AlEt 3 6

AlEt3/MPT (10/1) 8

AlEt 3 /PTES 'I 3

AlEt 3 /TMPip I' 5

External mmol / 1 oog

21

27

34

6

41

22

Contact conditions: T=50 'C; time=l hr; cat.conc.=4 g/1

Al/Ti=20 m.r.; solvent=hexane


We can also observe that in both series of experiments the best

catalytic systems (that is those that give the highest

isotacticity index and isotactic productivity) are those in which

the external base is able to be absorbed on the solid catalyst to

the largest extent. Moreover the external bases have different

behaviour depending on the solid catalyst they are contacted

with. In fact MPT, that can be noticeably absorbed on the first

catalyst, is hardly absorbed on the other one and PTES and TMPip

show opposite trend of absorption in the two series of

experiments.

CONCLUSIONS

The results mentioned above allow us to individuate some

general trends in the Lewis base activation mechanism:

i) The isotactic activation effect of the internal base may be

due either to the presence of the base itself on the isotactic

active sites or to the fact that the removal of the internal

base leaves active sites characterized by higher isospecificity

and/or higher stability with respect to the catalyst without any

base. The latter effect should prevail in the catalyst containing

a diester as an internal base since a noticeable octane insoluble

fraction is observed despite the fact that the diester is

strongly removed by AlEts.

ii) The variation of the extent of the first step stereoregula-

rity (e/t) with the external base confirms that the isotactic

activation effect of the external base derives by its direct

interaction with the active sites. However these e/t values

16. NMR Investigation 011 L.awis Rase Activation Effeci 197

depend not only on the characteristics of the.externa1 base but

on those of the internal base too.

iii) The isotactic activation effect of the external base has been

shown to be proportional to the base capability of being fixed on

the solid catalyst by replacing the internal base. Therefore

the fact that with a diester as an internal base the e/t values

of the octane insoluble fractions are lower than with EB could be

accounted for by the larger room due to the replacement of the

diester. However it is not possible to distinguish whether the

extremely high e/t values observed with EB as an internal base

are due to the smaller room left in the active site environment

by the replacement of the monoester or to the effect of both

internal and external base on the same active site.

iiii) From all the data observed it seems evident that the

effectiveness of a catalytic system depends more on the specific

pair of internal and external base than on the single internal or

external base. Moreover, while the amount of activation effect

clearly depends on the choice of the external base, the internal

base seems to affect prevailingly the stereoregularity of both

initiation and propagation.

EXPERIMENTAL

Reasents. The MgClz/TiClr catalyst containing Ti = 0.34%

was obtained starting from MgClz activated by 1 0 days of ball

milling in a roller-type milling machine. The MgClz catalyst

containing Ti=2.43% was obtained sterting from MgClz synthetized


by chlorination of the Grignard compound n-C4H9MgCl as described

in the patent literature.14 The catalyst containing ethyl

benzoate as an internal base (Ti = 1.33%, E.B. = 10.5%), was

kindly supplied by dr. Albizzati of Istituto G. Donegani, Novara.

The catalyst containing di(2-ethylhexy1)phtalate as an internal

base (Ti = 3.04%, DEHP = 17.9%), was prepared from soluble MgClz,

2-ethyl hexanol, phtalic anhydride and TiClr according to patent

1iterat~re.l~ A1(13CHzCH3)3 was prepared by reaction of

CH313CHzLi with AlC13 as reported in literature.16

pol- All the polymerizations were carried out in

a glass reactor containing 50 mL heptane as a solvent.

Al(13CHzCH3)s (Al/Ti = 20 m.r . ) , the Lewis base (base/Al = 0.3

m.r. with the catalyst containing EB and base/Al = 0.1 m.r. with

the catalyst containing DEHP) and the solid catalyst (0.2 9.)

were added in the said order. The reactor was filled with

propylene and the polymerizations were performed under

atmospheric pressure for 1 hr at room temperature. Different

conditions were used for run 4 of Tab.1. These conditions are

shown on the Table. The polymers were fractionated with boiling

solvents by conventional methods.

GEGAnalvsls, ' The polydispersity and Ew of all the heptane

insoluble/octane soluble and octane insoluble fractions were

determined by gel permeation chromatography (GPC) in 0-

dichlorobenzene at 135 'C, using a Waters 150-C gel permeation

chromatograph equipped with a Ultrastyragel column (106, 105, 104

and lo3 A' pore size).

-. The NMR samples were prepared by dissolving

ca. 100 mg of polymer in 1 mL of lr2,4-trich1orobenzene in a 10

16. NMR Iuvestigntion on h i s Base Actiwtion Effect 199

mm-0.d. tube. One half mL of CzDzC14 was added as a lock

solvent, and 1% of hexamethyldisiloxane was used as an internal

chemical shift reference. All the spectra were obtained by using

a Bruker AM-270 spectrometer operating at 67.89 MHz in PFT mode,

at a temperature of 115 'C.

Analvsis nf solid W v s t s , Four grams of solid

catalyst were placed in the reactor under nitrogen and the

temperature was raised to 50 'C. Then 950 mL of hexane and the

solution of AlEt3 or of the AlEt~/external base mixture were

added in the said order, reaching one liter total volume. The

reaction mixture was stirred for one hour at 50 'C, filtered and

washed several times with hexane at the same temperature and

dried under vacuum. The amount of base contained in the samples

so obtained were determined by GC.

REFERENCES

Sacchi,M.C.; Shan,C.; Locatelli,P.; Tritto,I. Macromolecules, 1989, in press.

Sacchi,M.C.; Tritto,I.; Locatelli,P. in "Transition Metals and Organometallics as Catalysts for Olefin Polymerization" W.Kaminsky, H.Sinn (Eds), Springer-Verlag Berlin, 1988, p.123.

Soga,K.; Sano,T.; Yamamoto,K.; Shiono,T. Chem.Lett., 1982 , 425.

Kashiwa,N. in "Transition Metal Catalyzed Polymerization: Alkenes and Dienes" ( R.P. Quirk, ed.), Harwood Acad. Publ., New York, 1983, p.379.

Barbe',P.C.; Cecchin,G.; Noristi,L. Adv. Polym. Sci. 1986, 81, 1.

Sacchi,M.C.; Tritto,I.; Locatelli,P. Eur. Polym. J., 1988, 24, 137.


(7) Tritto,I.; Locatelli,P.; Sacchi,M.C. "Int. Symp. on Transition Metal Catalyzed Polymerization", R.P.Quirk (Ed.), 1988, p.255.

(8) Zambelli,A.; Sacchi,M.C.; Locatelli,P.; Zannoni,G. Macromolecules 1982, 15, 211.

(9) Zambelli,A.; Locatelli,P.; Sacchi,M.C.; Tritto,I. Macromolecules 1982, 15, 831.

(10) Tritto,I.; Sacchi,M.C.; Locatelli,P. Makromol.Chem. 1986, 187, 2145.

(11) Sacchi,M.C.; Locatelli,P.; Tritto,I. Makromol. Chem. 1989, 190, 139.

(12) In fact it is well known that, while the activity referred to the entire catalyst increases with the titanium content, the activity expressed as the amount of polymer produced per titanium unit increases as the titanium content decreases.

(13) It must be said that the e/t values of the octane insoluble fractions are evaluated with a higher error than those of the octane soluble ones and of the heptane insoluble fractions.1.2 Indeed, due to the high molecular weight and to the high first step stereoregularity of these fractions, the smaller peak of the erithro resonance, in some cases, can be hardly detected.

(14) Soga,K.; Shiono,T.; Doily. Makromol.Chem. 1988, 189, 1531.

(15) Luciani,L.; Kashiwa,N.; Barbe',P.L.; Toyota,A.; German Patent 26431436, 1977.

(16) Blg. Pat., 895019, Mitsui Petrochem. Ind., C.A. 98, 2162126,

(17) Mole,T.; Jeffery,E.A. "Organoaluminum Compounds", Elsevier,

1983.

Amsterdam, 1972.

201

17. A New Electron Donor for the Stereospecific Polymerization of Propene

T. S U C A N O , Y. Y A H A H O T O , and T. F U J I T A

Y O K K A I C H I R E S E A R C H C E N T E R , H I T S U B I S H I P E T R O C H E H I C A L CO.,LTD.

N O . l T O H O - C H O , Y O K K A I C H I - S H I , H I E , 510, J A P A N

A B S T R A C T

We h a v e f o u n d t h a t t h e k e t a l c o m p o u n d , d i p h e n y l d i m e t h o x y -

nethane(DPDH!i),is u s e f u l f o r t h e s t e r e o s p e c i f i c p o l y m e r i z a t i o n o f

p r o p e n e . K i n e t c s t u d i e s a r e c a r r i e d o u t o n t h e r e a c t i o n o f D P D H H

w i t h a l k y l a l u n nium. T h e r e a c t i o n r a t e a n d t h e r e a c t i o n p r o d u c t s

a r e i n f l u e n c e d by t h e r e a c t i o n a t m o s p h e r e . T h e s t e r e o s p e c i f i c i t y

o f t h e p o l y m e r d e p e n d s o n t h e c o n c e n t r a t i o n o f D P D H H at t h a t time.

I N T R O D U C T I O N

T h e s t e r e o s p e c i f i c i t y o f h i g h l y a c t i v e HgClg s u p p o r t e d

c a t a l y s t is i m p r o v e d b y u s i n g v a r i o u s t y p e o f e l e c t r o n d o n o r ( E D )

a s m o d i f i e r o r c o a c t i v a t o r s . H a n y p a p e r s h a v e b e e n r e p o r t e d o n t h e

r o l e o f e l e c t r o n d o n o r s f o r t h e s t e r e o s p e c i f i c polymerization.'-''

K a s h i w a et a1 s u g g e s t e d t h a t e t h y l h e n z o a t e ( E B ) h a s t w o r o l e s , o n e

i s t o d e a c t i v a t e t h e n o n - s t e r e o s p e c i f i c c a t a l y s t c e n t e r s e l e c t i v e l y

a n d t h e o t h e r is t o l e a d t h e e n h a n c e m e n t o f t h e y i e l d .o'f i s o t a c t i c

p o l y m e r by d i r e c t p a r t i c i p a t i o n in t h e f o r m a t i o n of s t e r e o s p e c i f i c

c a t a l y s t c e n t e r s . S o g a et a1 s u g g e s t e d t h a t i n t e r n a l e l e c t r o n d o n o r

a n d e x t e r n a l e l e c t r o n d o n o r h a v e s l i g h t l y d i f f e r e n t roles. G u y o t e t

a 1 r e p o r t e d t h a t A l R a and t h e a r o m a t i c a c i d e s t e r f o r m s t h e b i n a r y

c o m p l e x e s and t h a t a d s o r p t i o n e q u i l i b r i u m o f c o c a t a l y s t c o m p o n e n t s

o n t h e s o l i d c a t a l y s t g o v e r n s t h e a c t i v i t y a n d s t e r e o s p e c i f i c i t y .

R e c e n t l y w e h a v e f o u n d t h a t t h e n e w e l e c t r o n d o n o r , d i p h e n y l -

d i m e t h o y m e t h a n e , is u s e f u l f o r t h e s t e r e o s p e c i f i c polymerization."

In t h i s p a p e r w e w i l l i n v e s t i g a t e t h e r e a c t i o n r a t e a n d p r o d u c t s

b e t w e e n D P D H H a n d A l R a , a n d w i l l d i s c u s s t h e r o l e o f D,PDHH i n t h e

202 T. Sugano, Y. Yamamoto and T. Fujita

s t e r e o s p e c i f i c p o l y m e r i z a t i o n .

E X P E R I M E N T A L

P r e p a r a t i o n o f S o l i d C a t a l y s t C o m p o n e n t

I n s t a i n l e s s - s t e e l pot (500 c m 3 i n s i d e v o l u m e ) c o n t a i n i n g 40

pi-eces of s t a i n l e s s s t e e l b a l l s ( 1 2 d i a m e t e r ) , 2 0 g o f a n h y d r o u s

M g C l g , a n d 4 c m 3 of d i b u t y l p h t h a l a t e ( D B P ) a r e c o - g r i n d e d f o r 2 4 h r s

u n d e r n i t r o g e n . 4 g r a m of t h e r e s u l t i n g s o l i d i s t r e a t e d by 2 5 c m 3

of T i c 1 4 a n d 2 5 c i a of h e p t a n e f o r 2 h r s at 8 O 0 C a n d w a s h e d w i t h

h e p t a n e . T h e t i t a n i u m c o n t e n t s of t h e c a t a l y s t is 1.28 % by w e i g h t .

P o l y m e r i z a t i o n

T h e P O y m e r i z a t i o n o f p r o p e n e is c a r r i e d o u t in a o n e l i t e r

s t a i n l e s s s e e l a u t o c l a v e . A l l r e a g e n t s a r e i n t r o d u c e d at r o o m

t e m p e r a t u r e u n d e r n i t r o g e n s t r e a m i n t h e o r d e r : a 500 C D a o f h e p t a n e

a 1 2 5 mg o f t r i e t h y l a l m i n i u m , a c e r t a i n a m o u n t o f e l e c t r o n d o n o r ,

a n d a 30 mg o f s o l i d c a t a l y s t c o m p o n e n t . T h e r e a c t o r is p r e s s u r i z e d

w i t h p r o p e n e ( 7 k g C ) and h e a t e d a t t h e p o l y m e r i z a t i o n t e m p e r a t u r e

( 7 O o C ) . T h e p r e s s u r e is k e p t c o n s t a n t d u r i n g t h e p o l y m e r i z a t i o n .

A f t e r t h e p o l y m e r i z a t i o n a l l s l u r r y s a r e e v a p o r a t e d a n d dried. T h e

i s o t a c t i c i n d e x ( 1 . 1 . ) is m e a s u r e d a s t h e f r a c t i o n b e i n g i n s o l u b l e

i n b o i l i n g h e p t a n e .

K i n e t i c s t u d y o f t h e r e a c t i o n of D P D M M a n d AlRa

In a o n e l i t e r a u t o c l a v e t h e r e a c t i o n b e t w e e n D P D M M a n d A I R 3

a r e i n v e s t i g a t e d in t h e s e v e r a l c o n d i t i o n s . R e a c t i o n m i x t u r e s a r e

s a m p l e d p e r i o d i c a l l y a n d a r e d e c o m p o s e d b y HoO. H e p t a n e l a y e r s a r e

a n a l y z e d by G a s c h r o m a t o g r a p h y and M a s s s p e c t r o s c o p y .

17. New E&nm Donor for h p y l e n e P o l ~ t i o n 203

R E S U L T S A N D D I S C U S S I O N

T a b l e 1 s h o w s t h e r e s u l t o f p o l y m e r i z a t i o n o f p r o p e n e w i t h o r

w i t h o u t s o m e k i n d o f e x t e r n a l .ED. T h e h i g h e s t s t e r e o s p e c i f i c i t y is

o b t a i n e d by D P D H H e s p e c i a l l y o n t h e c o n d i t i o n o f E D / A I = 0 . 5 , and t h e

p r o d u c t i v i t y is n o t s o lowered. But in t h e c a s e o f E B n o p o l y m e r is

o b t a i n e d o n t h e c o n d i t i o n o f m o r e t h a n 0.5 o f E D / A l m o l e ratio. T o

e l u c i d a t e t h i s d i f f e r e n c e t h e r e a c t i o n b e t w e e n D P D H H a n d A I E t a . By

u s i n g G a s c h r o m a t o g r a p h y a n d H a s s s p e c t r o s c o p y t h r e e k i n d s o f

p r o d u c t s a r e i d e n t i f i e d

1

as f o l l o w s :

2 3

Fig.1 s h o w s t h e d e p e n d e n c e o f t h e p r o d u c t s f r a c t i o n o n time.

T h i s r e s u l t s u g g e s t s that t h e r e a c t i o n o f D P D H H and A l E t a p r o c e e d s

a s f o l l o w s :

__t_

P h z C ( O t i e ) z

-.+--. P h 2 C ( O l e ) E r

0- - _- - P h n C ( 0 K e ) U

A

--+ --,, P h n C = C K e l l

0 1 1 2 1

T I M E ( H R )

FIC.1 D E P E N D E N C E O F T E E P R O D U C T S F R A C T I O N O N T I M E

( 7 O o C , u n d e r N 2 , A I E t a = O . 25(g/1), E D / A 1 = 0 . 2 ( H / H ) )

TABLE.l EFFECT OF ELECTRON DONOR FOR THE STEREOSPECIFIC POLYNERIZATION

CONDITION: SOLID C A T ( N g C 1 2 / D B P / T i C l r ) = 3 O m g 7 0" C , C3 = 7 K C , 1 E R

R U N ELECTRON DONOR ED/Al AIEtt PRODUCTIVITY(g/gCAT) I. I. (mole r a t i o ) (g/l) ( a t % )

OVER ALL ISOTACTIC ATACTIC

1 NO 0 0. 25 5,000 3,625 1,375 72. 5

2 Phn C (0Ne)n 0.1 0. 25 6,500 6,208 2 92 95.5

3 0. 25 0. 25 6,000 5,850 150 97.5

4 0. 50 0. 25 4,500 4,433 67 98. 5

5 PhCOOEt 0.1 0. 25 4,500 3,713 788 82. 5

6 0. 25 0. 25 4,000 3,540 460 88. 5

0. 50 0. 25 NO POLYHER 7

2 D

W

9

8 P h S i (0Et)o 0. 1 0. 25 7,500 7,200 300 96. 0

9 0. 25 0. 25 7,000 6,760 240 96. 6

17. New EIeCtron Donw fwpropUhe Polytneriurtkm 205

R E A C T I O N S C H E K E

PbC(OKe)p + AlEtj -------- PhzC(0Ke)Et + EtpAl(0Ke) (1)

OR

-+Ph2C(OKe)K + EtpAl(OKe) + GA4 t (2)

PhpC(0Ke)p t AlEtpH -------Ph:,C(OKe)H + Et2Al(OKe) (3)

PhpC(0Ke)Et + AIEta -------) PhpC=CH-Ke + EtzAl(0He) + 7 (4)

A s p r o d u c t 2 is p r o d u c e d o n l y at t h e b e g i n n i n g , t h i s r e a c t i o n

p r o c e e d s by t h e s c h e m e 3 , n o t by t h e s c h e m e 3. T r i e t h y l a l u m i n u m n a y

c o n t a i n a b o u t 2 m o l e X of d i e t h y l a l u m i n i u m h y d r i d e . P r o d u c t 3 is n o t

d e t e c t e d u n t i l m o s t o f D P D H H d e c o m p o s e , so t h i s m e a n s t h a t t h e

r e a c t i o n o f D P D H H and AlEtj p r o c e e d s c o n s e c u t i v e l y . T h i s may b e

b e c a u s e t h e r e a c t i v i t y o f s c h e m e 1 , 2 , and 3 is m u c h d i f f e r e n t a n d

D P D H H and A l E t j forms o n l y 1 : l c o m p l e x o n a c c o u n t o f t h e s t e r i c

h i n d r a n c e . I i s k o l a et a1 s u g g e s t e d t h e s i m i l a r r e s u l t o n t h e s t u d y

o f t h e c o m p l e x o f s i l y l e t h e r s w i t h A1Eta.6'

R e a c t i v i t y

PhpC(0He)p / A l E t p H > PhpC(0He)p / A l E t a > P h p C ( O H e ) E t / A l E ta

Fig.2 s h o w s t h e r e a c t i o n r a t e b e t w e e n D P D H H a n d AlEta. C i s

t h e c o n c e n t r a t i o n o f r e s i d u a l D P D H H at t h a t t i m e , a n d Co is t h e

i n i t i a l one. T h e In(C/Co) a g a i n s t t i m e is a s t r a i g h t l i n e , so t h e

o r d e r of r e a c t i o n is c o n c l u d e d t o b e o n e o n DPDKII. . A-

wi th C A T

. . . . . . . : E D / A 1 =O. 2

. . . . . . . . . . . . . . .

' --o-- - . . . . . . . . . . . . . . .

: E D / A I = O . 05

w i t h o u t C A T

u l i - - 3 T I K E ( I I R )

FIC.2 R A T E O F R E A C T I O N B E T W E E N D P D H H A N D AlEt:,


iI3-I I 1 I I I

2 3 4 0 I 3

T I H E ( I I R ) F I G S 3 E F F E C T OF 1 2 , ca

( A l E t a - 0 . 2 5 ( e / l ) , ED/AI=O. 2 , 7 0 O C )

U I T K O U T H2

U I T H C A T

U I T H Ca A

W I T H O U T 112

V I T H O U T C A T

.- - -... - _ - W I T H O U T 82

W I T H O U T C A T W I T H O U T Ca --*.- W I T H H 2

Y I T H O U T C A T

W ITK C a

W I T H c 3

F i g . 3 shows t h e d e p e n d e n c e on t h e r e a c t i o n a t m o s p h e r e . The

e x i s t e n c e of 10 f a i r l y e n h a n c e s t h e r e a c t i o n r a t e . To e l u c i d a t e

t h i s phenomenon t h e r e a c t i o n p r o d u c t s i s i n v e s t i g a t e d . T a b l e . 2

shows the r o l e f r a c t i o n of r e a c t i o n p r o d u c t s w i t h and w i t h o u t H 2 .

The main p r o d u c t i s n o t PhpC(0He)Et b u t PhgC(One)H, and t h e amount

o f t h i s p r o d u c t i s i n c r e a s i n g t o g e t h e r w i t h t h e r e a c t i o n t i m e .

T h i s r e s u l t s s u g g e s t t h a t Ha and AlEta h a v e s o r e i n t e r a c t i o n , t o

T A B L E . 2 R E A C T I O N P R O D U C T D I S T R I B U T I O N

C O N D I T I O N : AIEt ,*0 .25g/ l , E D / A 1 = 0 . 2 W I T H O U T C A T A L Y S T 7 0 a C , AFTER 1 . 5 l i R , U N D E R C3*5KgC

PRODUCT D I STR I B U T I O N C O N D I T I O N

Pb2C(One)2 PhpC(0le) E r P h 2 C (One) H Ph2C=CH-ne

U I T H O U T H2 0 .58 0.28 0. 1 4 0. 0

WITH H2 0.20 0 . 2 0 0. 61 0. 0 ( 8 ~ 0 1 % )

17. New Eketnm Damfor RopvCene PalymeriZah 207

m a k e complex o r t h e r e a c t i o n a s f o l l o w s :

A I E t a t Hp -----+ A1Eta:Hn

T h i s i n t e r a c t i o n seems t o have some r e l a t i o n s h i p w i t h t h e f u n c t i o n

o f m o l e c u l a r w e i g h t c o n t r o l r e a g e n t .

O n t h e c o n t r a r y t h e e x i s t e n s e of p r o p e n e s u p r e s s e s t h e

r e a c t i o n . S i m i l a r r e s u l t s was r e p o r t e d b y R.SPITZ e t a l . 4 0 6 ’ T h i s

r e s u l t a l s o s u g g e s t s t h e i n t e r a c t i o n o f AlEta w i t h p r o p e n e . T a b l e . 3

shows t h e r e a c t i o n p r o d u c t s u n d e r p r o p e n e a t m o s p h e r e . T h e p r o d u c t

a f f e c t e d b y p r o p e n e i s d e t e c t e d i n t h e p r o p e n e and A l E t a s y s t e m ,

b u t PhnC(OHe)CaH7 i s d e t e c t e d i n t h e p r o p e n e and A l i s o B u a s y s t e m .

A n d Al i soBu3 p r e m i x e d w i t h p r o p e n e p r o d u c e s o n l y PhtC(0He)H a n d .

PhpC(OHe)CaH?. T h i s r e s u l t a l s o s u g g e s t s t h e r e a c t i o n a s f o l l o w s :

AlisoBua + C a ---+ A1isoBua:Ca ---+ i s o B u ~ A l C a H ~ t i soC4

TABLE.3 R E A C T I O N P R O D U C T W I T H P R O P E N E

C O N D I T I O N : A l R a = O . 2 5 g / l , ED/A1=0.2 WITH C A T

70°C. A F T E R 1.5HR, U N D E R Ca=7KgC

PhpC(0He)n P h , C H P h g C C n H6 P h n C C a H7 P h p C C 4 He

One One One One ~ ~

A 1 E t a / Nn 0 . 18 0 . 1 1 0 . 70 0 0

A 1 i soBu3 / C a / H 2 0 . 51 0 . 17 ( 0 . 0 5 ) 0 . 1 9 0 . 0 9

AlisoBu3/Ca/Hn

( p r e m i x e d ) 0 . 4 9 0 . 3 4 0 0 . 18 0


1w-

n

= qJ- &

m c(

c(

v

- 80-

70

Fig.4 s h o w s t h e r e l a t i o n s h i p b e t w e e n t h e s t e r e o s p e c i f i c i t y a n d

t h e c o n c e n t r a t i o n o f DPDNN. T h e c i r c l e i s 1 . 1 . o f t h e p o l y m e r by 30

min.,which is p o l y m e r i z e d o n t h e c o n d i t i o n o f D P D N N / A l . T h e s q u a r e

d a t a is t h e c a l c u l a t e d 1 . 1 . o f t h e s e c t i o n s 1 polymer(1Ist.). T h e

c a l c u l a t i o n f o m u l e is a s f o l l o w s :

.................. ......... ... ,,-.. - , ........... ,. ....... ......... I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I . I I , , . -0 , * * .

. . . . . . . . . : : =: : : : : : : 9 * . d u r i n g t n a n d t n - l

. . . . . . . . . ' ' ' s e c t i o n a l p o l y m e r * . * . . . . . . . . . . . . . . . ,%:: . . . . . . . . . . . . . . . . . . * .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . o . . . . . . . . . . . . . . . . .

........... . - a _ - . . , * . . .............. .,_.. . ,, .......... _ ._ ,_ . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . rn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ' , . : : 1 : : : p o l y m e r . . . . . . . . . . . . . . . . . ................................. i - ~ . , ' - ...... . . . . . . . . . . . 3 0 @in. . . . . . . . . . . . . . . . . . . . . I * . . , I , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

* . . : : t : : : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I . a * I . , . . . . . . . . . . . . . . . . . . . , I , . . , . .

. . . . . . . . . . . . . . . .

I l t n = I s o t a c t i c I n d e x o f P t n p o l y m e r

P t n = t h e a m o u n t of p o l y m e r d u r i n g 0 t o t n h r

I l s t n = l s o t a c t i c I n d e x o f s e c t i o n a l p o l y m e r a t t n h r

P t n - P t n - 1 5 S e c t i o n a l p o l y m e r a t t n

= t h e a m o u n t o f p o l y m e r w h i c h is p r o d u c e d u r i n g

t h e t i m e o f t n a n d t n - 1

T h e s e d a t a s h o w f a i r l y g o o d c o r r e s p o n d e n c e . T h i s r e s u l t s u g g e s t s

t h e s t e r e o s p e c i f i c i t y o f t h e p o l y m e r h a s m u c h d e p e n d e n c e o n t h e

c o n c e n t r a t i o n o f DPDNN.

D P D N N / A l ( D P D N N t n / A l )

F I C . 4 DEPEND E N C E O F 1 . 1 . ON D P D H H /AI

DPDNNt. t h e c o n c e n t r a t i o n of D P D N N a t t h e t i m e t n - 1

17. New EIeCtron Donor for Propvlene Polyme?%zh 209

C O N C L U S I O N

We have found t h a t

1. PhpC(0He)n i s t h e u s e f u l e l e c t r o n d o n o r f o r t h e s t e r e o s p e c i f i c

p o l y m e r i z a t i o n of propene

2 . PhnC(0He)e r e a c t s w i t h AlEta and p r o d u c i n g f o l l o w i n g compounds

PheC(OHe)Et, PhpC(OHe)H, PhaC=CH-He

3. R e a c t i o n r a t e i s i n f l u e n c e d b y t h e a t m o s p h e r e

H2 i n c r e a s e s r a t e

C3 d e c r e a s e s r a t e

These e f f e c t s depend on t h e i n t e r a c t i o n of A1Ra and both

H2 a n d C 3

4 . S t e r e o s p e c i f i c i t y of t h e polymer produced a t t h a t t ime has

s t r o n g dependence on t h e c o n c e n t r a t i o n of r e s i d u a l PheC(OHe)e

R E F E R E N C E S

1 ) P . PIN0 R . H U L H A U P T A N C E W . C H E H . I N T . E D . E N C L . 19 (1980) 857

2 ) N.KASHIWA,J.YOSHITAKE " T R A N S I T I O N H E T A L C A T A L Y Z E D P O L Y H E R I Z A T I O N "

R . P. Q U I R K (1988) P 2 4 0

3 ) K.SUCA T S H I O N O Y . D O I H A K R O H O L . C H E H . 189 1531 (1988)

4 ) A . G U Y O T R . S ' P I T Z L . D U R A N E L J . L. L A C O H B E "STUDY I N SURFACE SCIENCE

A N D CATALYSIS 25" T . K E I I (1986) P147

5 ) E . I I S K O L A P . S O R H U N E N T . C A R O F F "TRANSITION HETALS A N D O R C A N O H E T A L L -

ICS AS C A T A L Y S T S FOR O L E F I N POLYHERIZATION" W.KAIINSKY ( 1 9 8 8 ) P 1 1 3

6 ) R . SPITZ J . L A C O N B E K. P R I H E T J. P0LYH.SCI. P O L H . C H E N . ED.22(1984)2611

7 ) USP4700515


211

18. Formation of Cationic Species and Additive Effect of Ethyl Benzoate on Polymerization of Isobutene and Styrene with Ti& - Alkylaluminum Catalyst

K.ENDO and T.OTSU

Department of Applied Chemistry, Faculty of Engineering, Osaka City

University, Sugimoto, Sumiyoshi-ku, Osaka 558, Japan

ABSTRACT

The polymerization of isobutene (IB) and styrene (St) was carried

out with TiC13, (C2H5)2A1C1, TiC13-(C2H5)2A1C1, and TiC13-(C2H5)3A1

catalysts. In the polymerization of IB, the catalytic activity de-

creased in the following order: TiC13 > TiC13-(C2H5)2A1C1 (Al/Ti =

3.0) > (C2H5)2A1C1 > TiC13-(C2H5)3A1 (Al/Ti = 3.0) = 0. This order

suggests that the polymerization of IB proceeds via a cationic mecha-

nism. TiC13-(C2H5)2A1C1 catalyst produced the new active species by

the reaction of TiC13 and (C2H5)2A1C1.

active species, the additive effect of ethyl benzoate (EB) on the poly-

merization of IB with TiC13 and TiC13-(C2H5)2A1C1 catalysts was in-

vestigated. The active species are inactivated selectively by the

addition of an adequate amount of EB. However, in TiC13-(C2H5)2A1C1

catalyst, excess EB destroyed even the coordination active species.

On the other hand, in the polymerization of St, the catalytic activity

decreased as follows: TiC1,-(C2H5),A1(A1/Ti = 3.0) > TiC13-(C2H5)2A1C1 (Al/,Ti = 3.0) > TiC13 > (C2H5)2A1C1.

with that of IB, suggesting that the polymerization of St with

TiC13-(C2H5)2A1C1 catalyst proceeds simultaneously through both the

cationic and the coordination mechanism. The additive effect of EB

was also different from that of IB, and a large amount of EB was

required to inactivate the cationic active species. On the basis of

these results, we concluded that the cationic active species originate

mainly from TiC13, and EB selectively inactivates such species.

In order to inactivate the

This order is not in agreement

INTRODUCTION

We have reported that many 2-olefins such as 2-butene (B2)

212 K. Endo and T. Otsu

undergo the monomer-isomerization polymerization with Ziegler-Natta

catalysts to give a high molecular weight polymer consisting of the

corresponding 1-olefin unit. In the monomer-isomerization poly-

merization, the concentration of 1-olefin is controlled by thermody-

namic stabilities, so that the system always contains a large amount

of 2-olefins. Nevertheless, they do not participate in the poly-

merization and serve as a diluent. The monomer-isomerization poly-

merization of B2 is induced by TiC13-(C2H5)3A1 catalyst even in the

presence of IB. 2, These facts strongly indicate that Ziegler-Natta

catalysts can cause highly selective polymerization of olefin isomers.

Such high selectivity of olefins toward Ziegler-Natta catalysts

proceeds, a

the polymer

case of Tic

merization.

This may be

well as the

lyst.

In this

provoked us to investigate the polymerization-separation of butene

isomers. 3,

similar, i.e the difference is 0.65OC, it is impossible to separate

them by conventional distillation. Fortunately, as described above,

the polymerization reactivities of the two olefins are different.

with TiC13-(C2H5)3A1 catalyst, the selective polymerization of B1

Since the boiling points of 1-butene (Bl) and IB are very

When polymerization of a mixture of IB and B1 was carried'out

d eventually B1 charged has been converted completely into

i.e. the polymerization-separation is performed. In the

3-(C2H5)2A1C1 catalyst, IB also participates in the poly-

explained by the fact that the cationic active species as

coordination species are formed in TiC13-(C2H5)2A1C1 cata-

Thus the polymer formed consists of both IB and B1 units.

study, the polymerization of IB, styrene (St) and a-methyl

styrene (a-MeSt) with various catalysts was undertaken to clarify the

formation of cationic species along with coordination species. Some

workers have reported on the polymerization of 1,l-disubstituted

ethylene and conclude that Ziegler-Natta catalysts serve as cationic

initiator. 4-12)

with alkylaluminums.

modified by electron donor have been published. 13)

show the effect on both the efficiency of the catalysts and the

stereospecificity of the polymers. Among them, ethyl benzoate (EB)

is one of the most effective electron donors on the isospecificity of' the poly(1-olefins). 14)

Most studies, however, deal with TiC14 in combination

A large number of papers and patents on Ziegler-Natta catalysts

Such compounds

In addition, such donors can also form a complex with Lewis acids

18. Effect of EB in TiCI,-Alkyhluminium Catalyst 213

such as TiC13 and alkylaluminum to suppress its cationic character. 13)

Thus, it is expected that the cationic active species derived from

Ziegler-Natta catalysts are inactivated by the addition of donors.

Then, the-. effect of EB on the polymerization of IB and St was also

investigated.

EXPERIMENTAL

Reagents IB, B1, St and a-MeSt were used after the fractional

distillation over calcium hydride.

Stauffer), and TiC13 (HA-type, Stauffer Chem.) were used without

further purification. Extra pure n-heptane, EB, and other reagents

were used after purification by the standard methods.

(C2H5)3A1, (C2-H5)2A1C1 (Toyo-

Polymerization Procedure Polymerizations were carried out in a sealed glass tube with shaking in a thermostat at a constant tempera-

ture for a given time. The required amount of reagents into the tube

was charged by a syringe, and the tube was sealed under high vacuum.

The catalyst after mixing TiC13 and alkylaluminum were aged for 30 min

at room temperature. Then EB was added and the catalyst aged for

another 30 min. After polymerization, the tube was opened and the

contents poured into a large amount of methanol to precipitate the

polymer formed. The polymer yield was calculated by the weight of

dry polymer obtained.

Characterization of Polymers The structure of the polymers was

checked by IR and 13C-NMR spectra.

mers was determined by GPC. Fractionation of the polymers was per-

formed with Soxhlet's extractor. Ether and methyl ethyl ketone (MEK)

were used for poly(B1) and poly(St), respectively.

The molecular weight of the poly-

15)


Polymerization of Olefins with TiC13-(C2H5)2A1C1 Catalyst

The polymerization of B1, IB, St, and a-MeSt was carried out with TiC13-(C2H5)2A1C1 catalyst in n-heptane at 60°C; the results are shown

in Table 1.

lysts of 1-olefins, B1 polymerized easily. Furthermore, IB and a-MeSt

polymerized with this catalyst despite of 1,l-disubstituted ethylenes,

suggesting that the polymerization proceeds v t a a cationic mechanism.

St also polymerized with TiC13-(C2H5)2A1C1 catalyst, although the

Since TiCl -(C2H5)2A1C1 is one of the isospecific cata- 3


rate of polymerization was slower than that of IB. Taking the poly-

merization reactivities of St into consideration, the polymerization

seems to proceed through both the cationic and coordination mechanism.

Table 1

catalyst in n-heptane at 60 "Ca)

Polymerization of olefins with TiC13-(C2H5)2A1CI

Olef ins Temp. ( "C) Time (hr) Yield ( X )

Bib) 80

IB 60

a-MeSt 60

St 60

2.0

2.0

2.0

2.0

78.7

82.4

14.0

16.9

a) Polymerization conditions; [Olefin] = 2 .0 mol/L,

[TiCl31 = 50 mmol/L, Al/Ti = 3.0 in molar ratio. b) [Bl] = 1.0 mol/L.

From these results, we suppose that TiC13-(C2H5)2A1Cl catalyst

has two distinct active species, i.e. one cationic and the other

coordination, and that they can operate independently and simultane-

ously, depending on the kind of monomer employed. Then, the poly-

merizations of IB and St were investigated in detail to elucidate

these points.

Polymerization of I B

Table 2 shows the results of polymerization of IB with various catalysts in n-heptane at 60°C. The order of catalytic activity is

as follows: TiC13 > TiC13-(C2H5)2A1C1 (Al/Ti= 3.0) > (C2H5)2A1C1 > TiC13-(C2H5)3A1 = 0 . One notes that the polymerization activity of

TiC13-(C2H5)2A1C1 is lower than that of TiC13.

acts as a main active species for the polymerization, TiC13-(C2H5)3A1

catalyst (Al/Ti=3.0) can also initiate the polymerization, because

(C2H5)2A1C1 is formed by the ligand exchange reaction between TiC13

and (C2H5)3A1.

catalyst, it is evident that the (C2H5)2A1C1 itself is not a major

cationic active species for the polymerization of IB.

If the (C2H5)2A1C1

Since the polymerization of IB did not occur with that

In the case of TiC13-(C2H5)2A1C1 catalyst, a new active species

is possible to be formed by the reaction of two catalyst components.

18. Effect of EB in TiCI,-Alkyhluminiurn Catalyst 215

Table 2 Polymerization of IB with various catalysts

in n-heptane at 6OoC for 2 .0 bra)

Cat a1 ys t Yield(%) Mn b, Mw/Mn b)

~~

TiC13 82.4 2200 11.7

(C2H5)2A1C1 4.0 33400 4.1

TiC13-(C2H5)2A1C1 3 0 . 3 - - TiC13-(C2H5)3A1 0.0 - -

a) Polymerization conditions ; [IB] = 2 .0 mol/L,

b) Determined by GPC

[TiCl31 = 50 mmol/L, Al/Ti = 3.0 in molar ratio.

In order to clarify this point, GPC measurement of the polymers was carried out and the elution curves are shown in Fig. 1. The curve

obtained with TiC13-(C2H5)2A1C1 catalyst gave the polymodal, and it

was not the same as those obtained with (C2H5)2A1C1 or TiC13 catalyst,

indicating that the reaction products also serve as the cationic

active species.

The catalytic activity of TiC13 decreased by the addition of alkylaluminums, but the effect between (C2H5)3A1 and (C2H,.)2A1C1

is different. Such difference may be explained by the formation of

a surface complex between TiC13 and alkylaluminums, preventing the

cationic polymerization based on TiC13. 13)

alkylaluminum to TiC13 seems to be related to the polymerization

activity of IB.

Although the actual structure of the active species for the

polymerization is uncertain, we deduced that the cationic active

species mainly originates from TiCl

Thus, the reactivity of

3' We studied the addition of EB as one way to inactivate the

cationic active species, and the results are depicted in Fig. 2 .

The polymerization of IB decreased markedly by the addition of EB.

In the TiC13 catalyst, no polymerization took place at EB/Ti molar

ratio of 0.4 or above. When TiC13-(C2H5)2A1C1 catalyst was used, a

little more EB was required to be inhibited completely the polymeri-

zation. This may be attributed to the presence of other cationic active species besides TiCl 3'


M. W.

106 Id lo4 Id lo2

Fig.1 GPC elution curves of poly(1B) obtained with

( 1 ) TiC13, (2) (C2H5)2A1C1, (3) TiC13-(C2H5)2A1C1 catalyst;

For polymerization conditions see footnote to Table 1.

501 I

EB/Ti molar mtio F i g . 2 Effect of EB/Ti molar ratio on the polymerization of I B with

( 1 ) TiC13 and (2) TiC13-(C2H5)2A1C1 catalyst in n-heptane at 60°C for 2.0 hr;[IB] = 2.0 mol/L, ITiC13] = 50 mmol/l, Al/Ti = 3.0 in molar

ratio.

The polymerization of B1 was carried out with TiC13-(C2H5)2A1C1 catalyst in the presence of EB (EB/Ti = 0.5) to clarify isospecific function of EB, and the results are shown in Table 3 . It was found

that EB serves as not only inactivator of the cationic active species

but also modifier of the isospecific polymerization.

18. Effect of EB in TiC13-Alkyklmminium Catalyst 217

Table 3

catalyst in n-heptane at 60 "Ca)

Polymerization of B1 and IB with TiC13-(C2H5)2A1C1

Olefin [EBI/[Til Time Yield Ether-insoluble

ratio (hr) (wt%)

B1 - 2.0 78.7 94.0

B1 0.5 2 . 0 72.5 96.7

IB 0.5 2 . 0 0.0 -

a) Polymerization conditions; [Olefin] = 2 .0 mol/L,

[TiCl31 = 50 mmol/L, Al/Ti = 3.0 in molar ratio.

However, in the polymerization of IB, the influence on the active species of coordination polymerization can not be discussed. So the

polymerization of IB and B1 mixture with TiC13-(C2H5)2A1C1 catalyst

was examined, and the results are shown in Fig. 3 . The content of IB

in the polymer obtained decreased as a function of EB/Ti molar ratio,

and a polymer consisting of only B1 unit was formed at its molar ratio

of 0.5 and above.

0 E

-60 - L

EB/Ti molar ratio

Fig. 3 Effect of EB/Ti molar ratio on the polymerization of IB-B1

mixture with TiC13-(C2H5)2A1C1 catalyst in n-heptane at 60°C for

4 . 0 hr;

in molar ratio.

[IB] = [Bl] = 1.0 mol/L, [TiC13] = 50 mmol/L, Al/Ti = 3.0


In a molar ratio from 0.5 to 1.0, the polymerization of B1 pro-

ceeded satisfactorily and no contamination of IB unit in the polymer

was observed from "C-NMR spectra of the polymers as shown in Fig. 4 .

Further addition of EB (EB/Ti > 1.0) decreased the catalytic activity

due to destruction the coordination active center, and eventially no

polymer was obtained (EB/Ti > 2.0). When acetophenone (AF) was used instead of EB, such selectivity

was not observed as shown in Fig. 5 . The resulting polymers always

contained an IB unit until no polymerization took place. Although

the IB content in the polymer decreased somewhat by the addition of

AF, the cationic active species were not inactivated completely.

Namely, AF destroyed active sites for both coordination and cationic

polymerization without selectivity.

Based on these results, we conclude that an adequate amount of EB

serves as a selective inactivator for the cationic active species, but

an excess of EB deactivates the coordination active center.

1

2 I

80 60 40 20 0 PPm

Fig. 4

catalyst without EB and (2) with EB (EB/Ti = 0.5).

"C-NMR spectra of poly( IB) obtained by TiC13-(C2H5)2A1C1

Polymerization of St St can polymerize with not only cationic but also coordination

initiators, so it is more interesting to study the polymerization of

St using TiC13 or TiC13-(C2H5)2A1C1 catalyst than that of IB.

shows the results of the polymerization of St with various catalyst.

Table 4

18. Efffed of EB in TiC13-Alkykaluniiniunr Cahbst 219

'ool'oo

AF/Ti molar ratio

Fig. 5 Effect of AF/Ti molar ratio on the polymerization of I B - B l mixture with TiC13-(C2H5)2A1C1 catalyst in n-heptane at 6OoC for

4 . 0 hr; [ I B ] = [ B l ] = 1 . 0 mol/L, [TiC13] = 50 mmol/L, Al/Ti = 3.0 in

molar ratio.

The catalytic activity was found to decrease in the following order:

TiC13-(C2H5)3Al > TiC13-(C2H5)2A1C1 > TiC13 > (C2H5)2A1C1. This order

is not in agreement with that of I B , suggesting that both coordination and cationic polymerizations take place simultaneously in the case of

TiC13-(C2H5)2A1C1 catalyst.

Table 4 Polymerization of St with various catalysts

in n-heptane at 60°C for 2 . 0 hr a)

Catalyst Yield MEK-insoluble

( % I (wt%)

TiC13 15.6 0.0

(C2H5)2A1C1 0.1 0 . 0

TiC13-(C2H5)2A1Cl 16.9 4 8 . 8

TiC13-(C2H5)3A1 42.5 72.6 ~~

a) Polymerization conditions; [St] 2.0 mol/L,

[TiC13] = 50 mmol/L, Al/Ti = 3.0 in molar ratio.


"1 \2

% $ 5 0 a \o

1 0 - 1

Since the polymerization of St with TiC13 catalyst proceeds only

v i a a cationic mechanism,

catalyst was examined. The results are shown in Fig. 6. No poly-

merization of St was observed at EB/Ti molar ratio of 4 . 0 and above.

In comparison with the polymerization of IB, a large amount of EB is

required to inactivate the cationic active species. This may be at-

tributed to the difference in cationic polymerization reactivity

between IB and St.

the additive effect of EB to TiC13

The additive effect of EB to TiC13-(C2H5)2A1C1 catalyst was also

studied, and the results are shown in Fig. 6. The polymerization

still proceeded in the presence of a large amount of EB, although the

polymer yield decreased as a function of EB/TI molar ratio. From the

inactivation effect of EB to TiC13 catalyst, the polymerization of St

with TiC13-(C2H5)2A1 catalyst at EB/Ti molar ratio of 2 .0 or above

seems to proceed through a coordination mechanism.

Fig. 7 shows the GPC elution curves of poly(St) obtained with

various catalysts. The MEK-soluble fraction of polymer obtained with

TiC13-(C2H5)2A1C1 catalyst gave a bimodal curve.

molecular weight corresponds to that of polymer obtained with TiC13

The peak of lower

*O:

Fig

( 1 ) 2.0

rat

6 Effect of EB/Ti molar ratio on the polymerization of St with

TiC13 and ( 2 ) TiC13-(C2H5)2A1C1 catalyst in n-heptane at 6OoC for

hr; [St] = 2.0 mol/L, [TiC13] = 5 0 mmol/L, Al/Ti = 3.0 in molar

0 .

18. Effed of EB in TiC13-Alkyhluminiurn Catalpt 221

and disappeared in the presence of EB (EB/Ti = 3.0). Taking the in-

activation effect of EB to cationic active species into consideration, this peak appears to be an atactic poly(St). We therefore conclude

that the addition of EB makes it possible to inactivate selectively

the cationic polymerization of St.

TiC13-(C2H5)2A1C1 catalyst can cause the highly isospecific poly-

merization of 1-olefins. Nevertheless, the isospecificity of poly(St)

obtained with TiC13-(C2H5)2A1C1 catalyst was lower than that obtained

with TiC13-(C2H5)3Al catalyst.

the polymerization of St using b-TiC13-based catalysts.

The isotacticity of the polymer did not also improve markedly by

the addition of EB as shown in Fig. 8. This behavior coincided with

that of polymerization with a highly active MgC12-supported TiC14

catalyst. 14)

Similar results have been reported in 10-12)

Consequently, the isotactic active species for one

monomer does not always serve as the active site for other monomers

Fig. 7 GPC elution curves of

poly(St) with (1)(C2H5)2A1C1,

(2)TiC13,(3)TiC13-(C2H5)2AlCl-

EB and (4)TiC13-(C2H5)2A1C1

catalyst. The polymers of

(3) and (4) are MEK-soluble

fraction.

- '0 1.0 2.0 3.0 4

EB/Ti molar ratio

Fig. 8 Effect of EB/Ti molar

ratio on MEK-insoluble fraction

of poly(St). For polymerization

conditions see footnote to Fig. 6 .


References

1. K.Endo and T.Otsu, "Handbook of Mass and Heat Transfer Vo1.3" Ed.

by N.P.Cheremisinoff, Gulf. Pub. Co.. Houston, Texas, 1989, p 552.

2. K.Endo and T.Otsu, unpublished results.

3. K.Endo and T.Otsu, Polym. Prep., Am. Chem. SOC., Div. Polym. Chem.

27(1), 383 (1986).

4. A.V.Topchiev, B.A.Krentse1, N.F.Bogornolova and Y.Ya.Gol'dfarb,

Dokl. Chem. Technol, 106, 659 (1957).

5 . R.Bacskai and S.J.Lapporte, J. Polym. Sci., Part Al, 2225 (1963).

6. M.Hamada and J.Gary, Polym. Prep., Am. Chem. S O C . , Div. Polyrn.

Chem. 9, 413 (1968).

7. Y.Sakurada, J. Polym. Sci., Part Al, 2407 (1963).

8. Y.Sakurada and M.Ueda, Kobunshi Kagaku, 20, 417 (1963).

9. Y.Sakurada, K.Irnai and M.Matsumoto, Kobunshi Kagaku, 20, 422

(1963).

10. S.Murahashi, S.Nozakura and K.Hatada, Bull. Chem. SOC., 'Jpn., 34,

939 (1961).

11. S.Murahashi, H.Yuki and K.Hatada, Kobunshi Kagaku, 22, 823(1965).

12. S.Murahashi, H.Yuki and K.Hatada, Kobunshi Kagaku, 23, 250(1966).

13. J.Boor,Jr., "Ziegler-Natta Catalysts and Polymerizations" Academic

Press, New York, N.Y., 1979, p.225.

14. N.Kashiwa, J.Yoshitake and T.Tsutsui, "Transition Metals and

Organometallics as Catalysts for Olefin Polymerization" Eds. by

W.Kaminsky and H.Sinn, Springer-Verlag, Berlin, Heidelberg,

1988, p33.

15. G.Natta, Angew. Chem., 68, 393 (1956).

223

19. Co- and Terpolymerization of Ethene and Higher a-Olefins with MgH2 Supported Ziegler Catalysts : New Mechanistic In- sight via the True Reactivity Ratios

G. Fink*, W. Fenzl, N. Herfert, T. Miiller, and I. Jaber.

Max-Planck-Institut fiir Kohlenforschung Kaiser-Wilhelm-Platz-1 D-4330 Miilheim a.d. Ruhr-1 FRG.

Copolymers of ethene with higher a-olefins, which are mainly

produced via heterogeneous Ziegler-catalysis, continue to be of

increasing importance; for instance, as substitutes for WC-polymers.

In copolymerization studies it has been shown that the copolymerization

parameters r1 for ethylene and r2 for all of the a-olefins differ by

orders of magnitudes; additionally, the values of the copolymerization

parameters were found to depend strongly on the chain length of the

a-olefin lS2). Moreover, the incorporation of the a-olefin was found to

decrease with increasing the carbon chain length 2! Attempts to

investigate and. understand in detail the above mentioned findings

mechanistically reveals that the co- and terpolymerization reactions

catalyzed by heterogeneous Ziegler-catalysis are very complex reactions;

and above all the methods used hitherto to determine the

copolymerization parameters have to be considered critically. Here new

basic questions concerning the methods used, may originate from

increasingly experimental evidences indicating that the active eites,

224 G. Fink, W. Fenzl, N. Herfert, T. Muller and 1. Jaber

located on the surface of a heterogenous Ziegler-type catalyst system,

are not uniform but consist of simultaneous different types, whereby

some are suitable for homopolymerization and others are more suitable

for copolymerization.

The determination of the true reactivity ratios is possible, at

the present, only by means of analysis of the polymer product formed

via the different active centres. This can be achieved by the analysis

of the 13C NMR spectrum for the unequivocal copolymer signals

assignments in the original polymer mixture, or for the isolated

copolymer signals.

The objective of this paper is to demonstrate how this right

way leads to the the estimation of the true copolymerization parameters

and how, as a consequence, new mechanistical details are obtained in

ethene / higher a-olefin copolymerization reactions using our highly

active MgH2 / TiCl, / AlE5 Ziegler-catalyst system. In previous

publications 3*4), whereby the homoplymerization of ethene was

reported, we demonstrated that the above catalyst system, which is

highly dispersed and starts with a high surface area of ca. 140 m2/g,

may have a model character for the investigation of the elementray

steps in heterogeneous Ziegler-catalyst systems.

A first simple kinetic scheme for the copolymerization of two

monomers, M, and q, with heterogeneous Ziegler catalysts can be

presented as follows:

19. TerpOlymeriZation of Olefins with MgH2 Supported Catalysts 225

kl2 R-M1-Kat t H2 ___C R-H2-Kat

k2 1 R-M2-Kat t Hl - R-Hl-Kat

k22 R-MZ-Rat t W2 ___C R-M2-Kat

Scheme (1)

The reaction of a monomer as deecribed in acheme (1) is a

compoeed quantiw of several elementary steps, (i.e., diffusion of the

monomer to the active centre, adsorption of the monomer on the active

centre and finally inaertion into the Ti-C-bond); hence, the propagation

conetanta, kij, in the above scheme are likewise corn@ quantities as

a result of the -ion, adsorption and insertion proceseee. We euppoee

that the adsorption behaviour of the relatively small ethylene molecule

in compaxision to the long a-olefin molecule may be different and

therefore the value of the term [MI, / M,, i.e., the initial monomer

concentration ratio, in the ~ a y o - ~ e w i s equation '1, scheme (2). may be

Werent on the surface of a heterogeneous Ziegler-catalyst and in the

reaction medium.

226 G. Fink, W. F e d , N. Herfert. T. Miiller and I. Jaber

For the follwing estimation of the copolymerization parameters

it is useful to discern between the overall or mixed parameters and the

true copolymerization parameters. First we assume that there are only

uniform active centres located on the catalyst surface, (i.e., one centre

model), and use ethene and comonomer peaks in the 13C NMR spectrum

of the polymer mixture for the estimation of the copolymerization

parameters according to the Mayo-Lewis equqtion ‘I. This evaluation,

via the r1 versus r2 diagram, leads to the overall or mixed

copolymerization parameters. However, for the estimation of the true

copolymerization parameters we now use the following considerations.

The Mayo-Lewis equation describes the composition of the copolymer

as a function of the initial monomers mixture and the copolymerization

parameters. If we know these and the monomers mixture we can

calculate not only the copolymer composition but also, by means of

statistical considerations, the sequence length distribution of M, and $ sequences in the copolymer ‘1.

Vice versa, it is of course possible to determine the r

parameters from a given experimental sequence length distribution and

the initial monomer composition. This is achieved in this paper by only

identifjring the monomer sequences, (e.g., triads), in the 13C NMR

spectrum and using only the intensities of the signals from the

comonomer unite. For example, for an ethene / 1-hexene copolymer, the

evaluation of the pp and gs peaks intensities to determine rl, and the

evaluation of the CH-peaks intensities to determine r2 is shown below,

scheme (3); (for 13C NMR nomenclature see ref. (71, and for the

different sequences see Table (I)).

CH (EHE)

CH (EHE) + CH (EHH) t CH (HHH)

Scheme (3)

This procedure for the determination of the r parameters in

copolymerization studies, via the sequence length analysis, leads to the

evaluation of the true copolymerization parameters. The first who

showed this useful technique were Cheng 8, and McLaughlin and

Vanderwal ’I.

The dependence of the mixed and the true copolymerization

parameters, in ethene / 1-hexene copolymerization, on the Ti loading

and the specific surface area of the MgH2 / TiCl, catalyst is shown in

Fig. 1. It is observed that there are considerable differences in the

values of the copolymerization parameters evaluated, especially between

the mixed and the true rl parameter. This finding confirms that we

have a polymer mixture between pure ethene homopolymer and ethene

/ 1-hexene copolymer. Consequently, this interesting result indicates

that we have different types of active centres; namely, centres for the

homopolymerization of ethene and others for the copolymerization of

228 G. Fink, W. F e d , N. Herfert, T. Miiller and I. Jaber

ethene with higher a-olefins, (two centres model). At low Ti loading the

surface area of the catalyst is high and the mixed r1 is high, this

implies that at low Ti loading the active centres present are mainly

ethene homopolymerization centres. The course of variation of the r1

and r, parameters with increasing the Ti loading and decreasing the

surface area demonstrates that we have decreasing

ethene-homopolymerization centres and increasing copolymerization

centres on the MgH, support.

The effect of the polymerization temperature on the values of

the mixed and the true reactivity ratios is shown in Fig. (2). It is

shown that the value of the mixed r1 parameter decreases rather

strongly with increasing the polymerization temperature. This

observation means that the copolymerization centres increase with

increasing the temperature. However an important result is that the

true reactivity ratios remain constant with increasing the temperature.

These results can be explained better by means of Fig. (31, i.e., the

Arrhenius plot of the rate constants derived from the copolymerization

parameters according to the two centres interpertation. From Fig. (3)

it is observed that the value of E,, and E,, is almost the same, i.e.,

49 and 42 kJ/mol respectively, and only half the value of either Ell

or Elr This means, concerning the mechanism of the copolymerization

centres, that we have a marked influence of the last inserted monomer

unit on the activation energy of the subsequent insertion steps.

Therefore, there is a Markov statistics of the at least first order. This

is a surprising result and indicates that when the last inserted unit is

an a-olefin then the subseqeent insertion of an a-olefin or ethene unit

is much easier than when ethene is the last inserted monomer unit.

19. TerpOlymerizatMn of Okfins with MgH, Supported Catalysts 229

Furthermore, this mechanism gives a good explanation of the

'synergistic effect' in the terpolymerization of ethene / a-olefin /a-olefin,

published for the first time by Seppluii lo) and confirmed later by Ojala

2), which suggested that the short chain has an accelerating effect on

the insertion of the long chain a-olefin in terpolymerization.

The next investigated reaction parameter is the dependence

of the mixed and the true r parameters on the conversion. In technical

processes a high degree of conversion is desired. The interesting result

in Fig. (4) indicates that with increasing conversion the concentration

of ethene homopolymerization centres decrease; this is strongly implied

by the observed fast decay of r1 with increasing conversion;

comparativly, the concentration of copolymerization centres remain more

or less constant with a slight tendency to increase, as is implied in the

plot of r2 versus conversion in Fig. (4). Using a TiCl, / MgH2 catalyst

system of 6.29 %Ti, It is possible that at the early stages of

polymerization we have both ethene homo- and co-polymerization

centres participating in the polymerization, however with increasing

conversion, the highly active ethene homopolymerization centres become

more and more surrounded by polyethylene.

The above evaluation of the mixed and the true reactivity

ratios in dependence of the reaction parameters, i.e., Ti loading,

temperature and conversion, is a first approach to identify different

active centres in copolymerization. The two centres model is a first and

simplest estimation. The reality aims at a multiple site model.

230 G. Fink, W. Fenzl, N. Herfert, T. Miiller and I. Jaber

Consequently, it is necessary to fractinate the polymer mixture

in order to try to isolate the different polymer fractions formed by

different active centres. The fractionation of an ethene / l-octene

copolymer using a temperature and a solvent gradient are shown in

Table 11. Indeed the results show that there are about three polymer

fractions: i) a copolymer fraction with 17-19 mo1% octene, ii) a

copolymer fraction with about 12 mol% octene and iii) a copolymer

fraction with 2-3 mol% octene. The evaluated copolymerization

parameters agree quite well with results obtained h m the copolymer

fractionation; that is, the higher the octene content in the copolymer

fraction , the lower is the r1 parameter. The true rl value in Fig. 1

aims, with increasing Ti laoding, at the true r1 value of 26 for the

17-19 mo1% octene containing polymer as is shown in Table 11.

Finally Fig. 6 shows the dependence of the mixed and the true

rl parameters on the conversion, in relation to the AyTi ratios of 5:l

(0 ,o) and 20:l (x,A). Here we have tried to investigate a possible

dependence of the copolymerization parameters on the overall

concentration of the active species. The results in Fig. 5 show that the

effect of both AIR'i ratios on the r1 parameter with increasing

conversion is the same. In other words, with increasing the AyTi ratio

both of the ethene homopolymerization and copolymerization active

centres increase simultaneously.

In order to obtain more information about this difficult theme,

we tried to get some data on the concentration of active centres, [C'],

by the 14C0 radio-tagging technique using our highly active MgH2 /

TiC1, / AlEt3 Ziegler-catayst system. The experimental procedure for

the determination of [C'l in ethene polymerization using the above

system has been published recently ll). The effect of varying the [Ti]

on [C'] is shown in Fig. (6). Keeping all other polymerization conditions

constant, it is observed that [C'] increase steadily with increasing the

absolute W]. This finding implies that there is more effective usage and

participation of the Ti atoms in forming active species at high Ti concentration.

Also the effect of varying the Al/"i ratio on [C*] is shown in

Fig. (61, it is observed that the concentration of active centres increase

sharply with increasing the Al/Ti ratio in the range 5-20, it can also

be seen that an optimal of 20-50 Al/Ti ratio has to be used in order

to generate a maximum number of active centres in the MgH2 / TiCl,

/ AlEt3 catalyst system. Increasing the Al/Ti ratio above 50 leads, as

is found, to a reduction in [C'l. The plot of [C'l against AyTi ratio in

Fig. (6) shows an Al-isotherm type of curve, whereby the saturation

stage starts with an Al/"i ratio of 20. Furthermore at high [AlEt3]

competition between the AlEt3 and the monomer for adsorption on

active sites may result in preventing the monomer from coordinating

with active centres, as has been already emphasized by Tait et al 12!

Additionally, the studies on ethene / 1-hexene copolymerization indicate

that with increasing the AbTi ratio, both of the homo- and

copolymerization centres tend to increase, (see Fig. (5)). Investigation

into this area will be presented in another publication in the future 13).

Another interesting theme is the dependence of [C'I on the

Ti loading the surface area of various MgH2 / TiCl,

Ziegler-catalyst systems. Fig. (7) below shows that the activity of ethene

232 G. Fink. W. Fenzl, N. Herfert, T. Miiller and I. Jaber

polymerization decreases quite sharply with increasing the Ti loading

and decreasing the surface area. Investigation of this parameter with

the 14C0 radio-tagging method reveals that the reason for the observed

reduction in the polymerization activity, with increasing the Ti loading,

is unequivocally due to a dramatic reduction in [C*l but not to any

fundamental change in the value of kp, as is shwon in Fig. (8). Earlier

in the present publication, it has been shown that in ethene / 1-hexene

copolymerization the true r1 decreases whereas the true r2 increases

with increasing the Ti loading, (see Fig. (1)); these results strongly

indicate that at low Ti loading there are higher number of ethene

homopolymerization centres; whereas at high Ti loading there are fewer

homopolymerization centres but more copolymerization centres. At this

point one may raise the question: Could it be possible that the reason

for the drastic reduction of [C'I, occuring as a result of increasing the

Ti loading, is due to the probability that the 14C0 is labelling only part

of active centres but not all ?. This will be discussed in a further

publication in the future 13).

19. TerpOlymeriZntMn of Olefins with MgH2 Suppmted Catcrlyst~ 233

REFERENCES:

Bbhm, L. L., J. Appl. Polym. Sci., 9, 297 (1984). Fink, G., Ojala, T. A., in "Transition Metals and Organometalice

as catalysts for Olefin Polymerization", ed. by W. Kaminsky and

H.-J, Sinn, Springer-Verlag, Berlin (19881, p 169.

Kinkelin, E., Fink, G., Bogdanovic, B., Makromol. Chem., Rapid

Commun., 7, 85 (1986). Fink, G., Kinkelin, E., in "Transition Metal Catalyzed Polymerization:

Ziegler-Natta and Metathesis Polymerizations", ed. by Quirk, R. P.,

Cambridge University Press, Cambridge (19881, p 161.

Mayo, F. R., Lewis, F. M., J. h e r . Chem. SOC.., @, 1694 (1944).

Vollmert, B., Grundria der Makromolekularen Chemie, Band I,

E. Vollmert-Verlag, Karlsruhe (19801, p 137.

13C NMR Nomenclature: Carmen, C. S., Wilkes, C. E., Rubber Chem.

Technol., 44, 781 (1971). a) Cheng, H. N., in "Transition Metal Catalyzed Polymerizations",

ed. by Quirk, R. P., MMI press, Midland (19831, part B, p 617.

b) Cheng, H. N., J. Appl. Polym. Sci., 35, 1639 (1988). c) Cheng, H. N., J. Polym. Sci., Polym. Phys. Ed., 21, 573 (1983). d) Cheng, H. N., Anal. Chem., 8, 1828 (1982).

McLaughlin, K W., and Vanderwal, R. P., Poster at the Symposium:

"Metals in Olefin Polymerization", sponcored by Division of

Inorganic Chemistry, American Chemical Society, Denver, Colorado,

April (1987).

SeppBlil, J. V., J. Appl. Polym. Sci., 31, 667 (1986). Jaber, I. A., Fink, G., Makromol. Chem., "in the press", (1989).

Mckenzie, I. D., Tait, P. J. T., Burfield, D. R., Polymer

- 13, 307 (1972).

Jaber, I. A., Fink, G., to be published.

234 G. Fink, W. F e d , N. Herfert. T. Miiller and I. Jaber

Table (I)

13C NMR Spectra of Ethedl-Hexen-Copolymers

Line

7

8

9

10

11

12

13

14

15

16

1:

18

19

20

21

22

23

24

Tvpe Sequence

CH3

HHHH

nnHE

EHHt

&HE

EHH

HHtH

HHH

HHLE

HHL

EHEH

EHEE

EHE

nnn HEEH

HGEt

EEG

EHE

EHH

HHH

EHEE

HHEE

EHEHE

EHEHH

HHEHH

EHE

EHH

HHH

EHE

EHH

HHH

Chemical Shift

41,2

40,6

40,o

37,9

35,6

35,l

34,8

34,l

34,3

33,9

33,2

30,7

30,2

29,7

29,3

29,l

28,9

27,O

2 6 , 8

24,3

24,l

24,O

23,l

13, 9

19. TapoIymeriZntMn of Olefins with MgH2 Supported Catalysts 235

Table (11)

Fractionating apparatus according "Holtrupp" (Makrom. Chem. 178,2335( 1977))

Fractionating solvent: p-xylene / ethylene glykol monoethylether (EGME)

a) Fractionating using a temperature gradient

Fraction p-Xylene Temp Yield

Nr /EGME .C B

1 m30 30 tracer

2 7030 50 ca.O.4

3 m30 70 ca.O.1

4 m30 90 ca. 0.2

5 7030 110 ca.03

6 m30 UO ca.03

7 1m.o 130 ca.o.5

b) Fractionating using a solvent gradient.

Fraction p-Xylene Temp Yic.,

Nr /EGME 'C B

1 m.60 125 u.02

2 m40 125 ca. 1.3

3 m30 125 ca.0.2

4 mm 125 ca. 0.2

5 90: 10 125 ca.o.2

Mot96 Oden

IR NMR

18.1

14.9 12.8

11.5

8.6

3.4 2.9

3 3

2.5 1.9

MoI% Octen

IR NMR

19.0

17.0

2.5

Fractionating time: 25 min

Copolym. Parameters

rl mixed rl true r2 true

6 6 2 9 0.021

322 62 0.008

492 1 u 0.008

Fractionating time: 20 min

Copolym. Parameters

rl mixed r1 true r2 true

41 26 0.016

47 26 0.020

372 139 0 . 0

236 G. Fink, W

. Fenzl, N. H

erfert, T, Muller and I. Jaber

0

N

L

-0-

t-

8

F

L

0

I

Y

Ic

L a

v)

m

Q I-

F c

0. 2

c

1 0

0

0

0

N

c

0

0

0

0

4

m

19. TetpolynrerizatiOn of Okfim with MgH2 Suppotted Catalysts 237

600 -

500 -

400 -

300-

200 -

100 -

X

' 1 r l

X

0 0 0 0

i I I 1 I -

X

0,012 - 0,o 11 - 0,o 10 - 0,009 - 0,008-

0,007 - 0,006 - 0,005 - 0,004 -

0,003-

0,002-

Calalysl MgIi/TiCI,/AIEI, 4.52 W.% TI

A

X

Llie rue ( 0 ) r1 Parameter on Temperature

r2 X

X

X

0,oo 1 X

I I I I I - 30 4 0 50 6 0 - 7 0 T I " C 1

L)el)eiitlence of the mixed ( X - from the r2/rl - Diagram ) and

Llie rue ( 0 ) r2 Parameter on Temperature

Figure (2)

C a i y r i M~H~TCI,.AIEI, 4 52 mu. ~i s . 129 mZa

- 5 1 3 5 x 1 O A

Kinetic AnaPpls Two Centers Mocel

WimF

Rate Comtsnts ot the Capolymrkatkm of Ethrne (1) and l-tiorma (2) in U W a )

30 145: 35 2 , l t 1 . 0 53Ot 90 3,dGi.O 950t 250 40 515 i l25 7 . 6 t 4 , 0 05ot200 6 , b O . S 12402 300

SO 1400i?.SO 20.Oi10.0 1725t600 11 .6 t6 .0 1320, 600

60 2 8 1 9 7 0 0 41,4+tO,O 1795t900 12.Zi6.5 4015ilOOO

70 1985iSOO 27,2*14,0 2 3 C O i O O O 13 ,5 t7 ,5 307W 750

N w 01

r

z V z

Figure (3)

............

19. TerpolymerLntion of 0kfin.s w

ith MgH

2 Suppot.ed Catulysts

239

x 0

---6

-

x 0

X

0

0

............

0

0

- 0

0

0

I

-c

I X

X

c

0

e 8

0

0

0

0

4

m

c

0 0

m

N

L

s 'i c X

0

I-

0

9

0

In

0

4

0

m

0

N

9 s \

4

0

+

X

0

I-

0

9

0

ul

0

4

0

m

0

N

0

v-

240 G . Fink, W. F e d , N. Herfert, T. Muller and I. Jaber

Ksblysator

rl

180

160

140

1 20

100

80

60

40

20

X io 0

: MgII,/TICI,/AIEl,

7.15% Ti

: 5 : 1 20:l

: 011 0.61 ninl/l

: 025 ninl/l

: 8.15

: 39.5 'C

: 19.6 22.4 K

: 3.15 3.W mnl/l*s

: 7.18 1.15 mol/l*o

X

0

+ t

A

i t

2 4 6 10 12 14 x,

Mixed ( o x ) and true ( 0 A ) r, parameters of ethene / 1-hexene copolymers in dependence on conversion at different ratios AI:li.

0 1 I I I I I

0 0,l 02 03 Q4 QS 1o3ui i in mot/\

.- c I

qi I I I I

0

0 20 4 0 60 ao AIEt3 / T i ratio

Figure (6)

f

€ 3 f +I I I I 1 I I I

4 5 6 7 8 9 10 Titanium content in wt. %

96 68 55 34 34 39 Surface area in m*/g

Figure I. Variation of the polymerization activity with the Titanium content

and the surface area of various TiC14/Mg$ supported catalyst systems.

Conditions: [Ti] = 0,4 x 10-3mol/l, A l E P = 20, temp. = 313 K, time = 20 min., contact time = 60 min.

F 5

T I -

i

I ? E I I I I I 1

4 5 6 7 8 9 10

LOO

1

$ 300 n.

2c

2 00

100

0

I 1

T i i I

+I , I I 1 I 1 I 4 5 6 I 8 9 10

Titanium content in wt. %

I 1 I I I I 55 34 34 39 90 68 55 34 34 39 Surface area in d/g

I I I I I I 90 68 Titanium content in wt. %

Surface area in m*/g


245

20. Co- and Terpolymerization of Ethylene, Propylene and Buta- diene with Supported Titanium Catalyst

SHANGAN LIN, QING WU and LIXIN SUN

Institute of Polymer Science, Zhongshan University,

Guangzhou, China

ABSTRACT

The ethylene-propylene (EP), ethylene-butadiene (EB)

and propylene-butadiene (PB) copolymerizations and ethylene-

propylene-butadiene (EPB) terpolymerization with a supported

catalyst, TiC14/MgC12/ethyl benzoate-A1Et3, are described.

The catalytic activities were enhanced in the EP

copolymerizations, while the catalytic activities were

decreased in the co- and terpolymerizations containing

butadiene as compared with the corresponding

homopolymerizations. It was found that the butadiene units in

these co- and terpolymers are mostly in trans-l,4

configuration and long blocked sequences.

INTRODUCTION

The copolymerizations between monoolefins and dienes

have been considered to be of practical and theoretical

importance. As reported in the ethylene-

butadiene and propylene-butadiene copolymers can be prepared

with conventional Ziegler-Natta titanium-based or vanadium-

based catalysts. The copolymer composition and monomer

sequence distribution strongly depend on the catalyst system

and polymerization conditions. Alternating copolymers were

synthesized when the catalyst components were mixed at the

temperature below -7OOC and the polymerizations were carried

out at -5OOC to 0 5 , while random or block copolymers were obtained at higher temperature.

In recent years, highly active catalysts containing

titanium chloride supported on anhydrous magnesium chloride

have attracted extra attenti~n~-~) and have been intensively

246 S. Lin. Q. Wu and L. Sun

studied for olefin homopolymerizations and copolymerizations.

But, the behaviors of copolymerizations between monoolefins

and dienes on these catalysts are less understood. In this

paper, the behaviors of the co- and terpolymerizations

between ethylene, propylene and butadiene on a MgC12-

supported titanium catalyst and the microstructure of the

products are reported.

EXPERIMENTAL

Polymeric grade ethylene, propylene and butadiene were

purified by passing through molecular sieve column and

triethylaluminum (AlEt3) solution. Heptane was dried and

deoxygenated by the usual methods. A1Et3 and TiC14 were

commercially obtained and used without further purification.

Supported catalyst was prepared by co-milling anhydrous

MgC12 and TiC14 together with additive ethylbenzoate.

The polymerizations were carried out in a 250 ml glass

reactor equipped with a stirrer. A given amount of A1Et3 and

the supported catalyst was introduced into the reactor

containing the saturated solution of heptane with the

monomers. The gas mixture of the monomers was continuously

supplied to maintain a total pressure of 820 mmHg during the

polymerization. The polymerization was performed at definite

temperature for 1.5 h.

The product compositions were determined by IR

spectrophotometer (Nicolet 1 7 0 SXFT). 3C NMR spectra were

measured in o-dichlorobenzene at 1 2 0 OC with Bruker-200

spectrometer operating at 50 MHz. The molecular weight

distributions were measured at 135 OC by GPC (Waters

Associates 150C) using o-dichlorobenzene as solvent.


Polymerization of monomers The activities of ethylene homopolymerization and

propylene homopolymerization with this catalyst are quite

high and enhanced by copolymerizing each other. Fig.1 shows

20. Terpolymerization of Okfins with Suppotted Ti Cohlyst 247

the changes of the catalytic activity as a function of

monomer composition for the EP copolymerizations. Over a wide

composition range , the catalytic activities of the EP copolymerizations are much higher than that of the

homopolymerization of either monomer. The enhancement of the

catalytic activity in the copolymerization of ethylene with

a-olefins has been considered to be of increase of active

center concentration and activation by the comonomer as a

promotor’-’ 0 ) . The rate of ethylene polymerization was increased not

only in the presence of propylene, but also when the

propylene was removed. Fig.2 shows a result from the

experiment in which propylene was introduced into the system

after 3 0 min of ethylene homopolymerization for 5 min and

then throughout removed by vacuation and replacement with

pure ethylene. By the treatment, the rate of ethylene

polymerization went up remarkably. The behavior is different

from that with soluble Zr catalyst l o ) . Catalyzed by Cp2ZrCl2- methylaluminoxane, the enhanced rate of ethylene

polymerization returned rapidly to the original level by

stopping the supply of propylene.

Similar behavior was observed in the propylene

polymerization promoted by ethylene. As shown in Fig.3, the

rate of propylene polymerization after being promoted by

ethylene is also higher than the original rate, but the rate

enhancement in propylene polymerization is much smaller than

that in ethylene polymerization.

The EP copolymerization rate with time showed decay

type characteristics. Fig.4 shows the rate-time profile of

the EP copolymerization and those of the corresponding

homopolymerizations. In the decay period, the decrease of the

EP copolymerization rate with time is even rapider than that

of propylene homopolymerization rate. The decay kinetics can

be described by the following equation’’

where Ro, Rt and %, are the rates of polymerization at time=O

Rt= I$, + (Ro- %, ) .-kt

248 S. Lin, Q. Wu and L. Sun

0 20 40 60 80 100

P mol%

Fig.1

Polymn. conditions:[Ti] =0.03 mmol/L; Al/Ti=150; T=50°C.

P l o t of catalytic activity vs. monomer composition for EP copolymerization.

2ol adding propylene

I removing 8 g 10 propy lene

I + \ % - I t I t

0 20 4 0 60 80

Time, min 2

Fig.2 Promoting effect of propylene on the ethylene poly-

merization rate. ( 0 ) conventional homopolymerization of ethylene,

(0) polymerization of ethylene after being promoted by propylene.

20. Terpolymerizaticn of Okfins with Supported Ti Catalyst 249

a o

a W 0

a, c,

: 5 I

I I 1 I I

2 0

10

0

\

O\

O\

I I I I

0 20 4 0 60 80

Time, min

Fig. 4 Rate-time profiles of ethylene ( 0 ) , propylene (A) homopolymerization and EP copolymerization (0).


(starting decay), t and-, and k is decay rate constant. The

parameters, R,and k, were calculated by fitting the

experimental data of Ro and Rt to the equation. The results

fyomthe fittingare showninFig.5 and the optimum values of

the parameters are listed in Table 1.

However, the addition of butadiene into the

polymerization systems substantially lowers the catalytic

activity, though this catalyst is quite efficient for the

butadiene homopolymerization. For the EB and P B

copolymerizations, the changes of the catalytic activities

against butadiene content both appear as the saddle curves,

as shown in Fig.6. The reductions of the catalytic activities

in the presence of butadiene are attributable to the stronger

action of coordination of butadiene monomer towards Ti active

centers and lower chain-growing rate of the addition

butadiene. The EPB terpolymerization showed a similar result.

Substitution of toluene for heptane as polymerization

medium resulted in increasing the catalytic activities almost

doubly for the EB and PB copolymerizations and EPB

terpolymerization. The increases of the catalytic activities

may be attributed to the greater solubilities of the monomers

and greater swelling of the produced polymers in toluene.

The relationships between the polymer composition and

monomer ratio for these three copolymerizations are shown in

Fig.7. Based on the polymer composition and monomer

concentration data, the apparent reactivity ratios were

determined according to the method of Fineman-Ross '*I. For

these three copolymerization systems at 55OC in heptane, the

values of reactivity ratios are listed in Table 2.

Microstructure of products The IR spectra of the EB, PB and EPB samples reveal

that the butadiene units in these products are mostly in

trans-l,4 configuration. There exist the absorption bands at

770, 1054 and 1235 cm-' attributed to crystalline butadiene-

butadiene sequences in a wide range of butadiene content.

20. Terpolymeriurtion of Olefins with Supported Ti Catalyst 251

3

2

1

2 0 I

a c d

c,

-1 -

0 20 40 60 80

Time, min

Fig.5

polymerization (.) and EP copolymerization (0).

Plots of ln(Rt-R,) vs. time for propylene homo-

Table 1 Parameters of decay kinetics

P mol% RO R, k (mol/mol-Ti. s ) (mol/mol-Ti. s)

RO-R, R-

0 4.47

10 50.2

23 48.3

45 33.0

55 31.3

63 23.8

80 11.2

100 4.38

3.21*

13.3

10.7

6.50

5.50

3.67

2.25

1.03

0.28

0.028 0.74

0.045 0.78

0.042 0.80

0.046 0.82

0.058 0.85

0.047 0.80

0.039 0.77

* Polymerization rate at 90 min.

Table 2 Apparent reactivity ratios

1 r2 ‘122 System r

ethylene (1 1 -propylene (2) 1 1 - 9 0.18 2.1

ethylene (1 1 -butadiene (2) 53 0.25 13

propylene ( 1 -butadiene (2) 3.0 7.6 23

252 S . Lin, Q. Wu and L. Sun

I I I I

3 20 40 60 80 11

Bd mol% Fig.6

EB (01, PB ( 0 ) copolymerizations and EPB terpolymerization (A).

Polymn. conditions:

for EPB); [E]/[PJ=0.4 mol/mol in EPB.

Plots of catalytic activity vs. butadiene content for the

[Ti1 = O . 15 mmol/L; Al/Ti=150; T=50°C (55OC

P mol%

1 0 20 40 60 80 100

80 -

0 20 40 60 80 100

Bd mol%

Fig.7 Plots of polymer composition vs. feeding butadiene

content for EB (0) and PB ( 0 ) copolymerizations and feeding

propylene content for EP (0) copolymerization.

20. TerpolymerizatiOn of 0kfin.s with Supported Ti Gahlyst 253

Table 3 Fractionation results

~ ~~

PB product PP P Bd Fraction (wt%) (wt%) (wt%) Bd content qsp/c*

(mol%) (dl/g)

(a) boiling ether 32.5 0 39.4 16.5 0.86

(b) boiling chloroform 10.5 2.3 15.8 53.0 2 . 2 7

(c) boiling benzene 7.9 0.6 8.5 16.0 1.09

(d) 95OC toluene 40.3 6.5 21.4 15.5 1.65

(e) boiling toluene 8.5 6.8 2.1 '16.5 1.93

(f) boiling xylene 0 38.3 1.6 62.0

(4) residual 0 46.3 10.7 54.8

Measured in decalin at 135°C.

The products were fractionated by successive extraction

with a series of solvents and the solubility behaviors were

compared with that of the corresponding homopolymers prepared

under the same conditions. A typical result of the

fractionation of the PB sample is listed in Table 3. It can

be seen from the result that the solubility of the PB sample

is much different from that of a mixture of the two

homopolymers. It is worthy to mention that the propylene

homopolymer was completely dissolved after extracting by

boiling toluene, but the fractions of xylene extract and

residual of the PB sample still contain propylene units 38.0

and 45 .2 mol%, respectively. Furthermore, the IR spectra of all the fractions except the ether-soluble fraction exhibit

the absorption band of trans-1,4 polybutadiene crystalline at

770 cm-' and absorption band of polypropylene crystalline at

841 cm-l, as shown in Fig.8, indicating the presence of long

butadiene-butadiene sequences and long propylene-propylene

sequences.

Fig.9, 1 0 and 1 1 show the saturated carbon regions of

13C NMR spectra of the EB and PB copolymers and EPB

terpolymer. A common feature of these spectra is the strong

signal assigned to trans-1,4 butadiene units in homopolymeric

sequences at 32.9 ppm. The cis-I ,4 absorption at 27.6 ppm and


- 800 600 800 600

-1 cm

Fig.8 IR spectra of the extraction fractions of PB samples

in Table 3 .

1,2 absorption at 38.6 ppm are not detectable.

The spectrum of the EB sample containing butadiene

units 41 mol% (see Fig.9) shows two strong signals at 29.9

and 32.9 ppm and two weak signals at 29.4 and 32.7 ppm.

According to Bruzzone4), the resonance at 29.4

ppm is due to the methylene of ethylene units adjacent to

butadiene units and that at 32.7 ppm due to the methylene of

butadiene units adjacent to ethylene units.

In the spectrum of the PB sample with butadiene units

23 mol% (see Fig.101, there are several weak signals besides

the strong signal at 32.9 ppm and three groups of strong

signals assigned to the propylene units in the homopolymeric

sequences. The assignment of these weak signals could be

rationalized by using the parameters reported by Grant13) and

Gatti14). The chemical shifts of the methylene carbons of the propylene units 6- to a trans double bond are estimated as

37.1 ppm andy- to a trans double bond as 43.5 ppm in BPnb2

sequences, and as 36.3 ppm in BPB sequence. The observed

values are 37.0, 43.7 and 36.5 ppm, respectively. The

chemical shifts of the methylene carbon of the butadiene

20. Terpolymerization of Olefins with Supported Ti Cahbst 255

29.4ppm c I I

35 30 PPm

Fig.9 I3C NMR spectrum of EB sample with 41 mol% butadiene

43.7 40.1 36.5

40.3 37.0 30; 4 I I I

50 40 30 20 PPm

Fig.10 I3C NMR spectrum of PB sample with 23 mol% butadiene.

Y


I I I I

20 PPm 45 40 35 30 25

Fig.11 1 3 C NMR spectrum of EPB sample with 14.7 mol% butadiene.

I 1 I I I 50 45 40 35 30 25 20 ppm

Fig.12 13C NMR spectrum of EP sample with 35 mol% propylene.

20. Terpolpnerkatim of Okfiins with Suppmted Ti Catalyst 257

units adjacent to the methylene carbon of propylene unit are

estimated as 30.4 ppm,-and that adjacent to methine carbon of

Table 4 Diad distributions of EB and PB copolymers

E 0.59

B 0.41

EE =1/2 129.9 0.56

the propylene units as 40.1 ppm in BPnz2 sequences and as

39.8 ppm in BPB sequence. The observed values are 30.4, 40.3

and 40.1 ppm, respectively.

The diad distributions of the EB and PB copolymers

were calculated. The results shown in Table 4 clearly

indicate the blocky tendencies for butadiene and the

monoolefins.

The 13C NMR spectrum of the EP sample with 35 mol%

propylene is shown in Fig.12. The diad and triad

distributions and reactivity ratios calculated in terms of a

first-order Markovian process are shown in Table 5. The

copolymerization between the monoolefins proceeds more

randomly than the copolymerizations between the monoolefin

and diene. The data in Table 5 show that the EP

copolymerization behavior is somewhat different from that of

Soga's result with Ti ( O B U ) ~ / M ~ C ~ ~ / A ~ E ~ ~ C ~ - A ~ E ~ ~ ~ 5 , in which

rlr2 is near unity.

Fig.13 shows the DSC curves of the EPB terpolymers

with E/P=1.5. When the content of butadiene units reaches 6.3


Table 5 Sequence distributions of EP copolymer

E 0.65 EEE 0.39

P 0.35 EEP 0.20

EPE 0.10

EE 0.49 PEP 0.07

EP 0.33 PPE 0.12

PP 0.18 PPP 0.12 .................................................... r, =14.6 r2 =0.22 rlr2 =3.2

4 P I 1.5 117Oc

BD sol$

0

20.9

Fig.13 DSC thennograms of the EPB terpolymers

20. Terpol’tion of Olefins with Suppmted Ti Caknjst 259

m o l % , an endotherm peak caused by the crystalline

metamorphism’ ’of butadiene blocks appears at about 61’ C. The

melting point of the butadiene block crystalline ranging from

132-1 45 ‘?2 depends on the butadiene content in the polymers.

The crystallinity of the terpolymers is also conformed by X-

ray diffraction measurement. Fig.14 shows the X-ray diagram

of the EPB sample with butadiene unit 14.7 mol%. Two peaks

appear at 21.4O and 22.4O(28), respectively referring to the

polyethylene-type crystal and polybutadiene-type crystal.

1 I

15 20 25 28

Fig.14 X-ray diagram of t h e EPB sample with 14.7 mol% butadiene

MW

Fig.15 GPC curves of the EP copolymer (- 1 and EPB terpolymer ( ---- 1 . E/P = 1.5


Fig.15 shows GPC curves of the EP copolymer and EPB

terpolymer with 9.8 mol% Butadiene. The molecular weight

di,stribution of the EPB terpolymer appears as a nonuniform

modal and the amount of lower molecular weight fractions

increases as compared with the EP copolymer.

Introduction of the unsaturated double bond into the

polymer chains makes these copolymers easier,to be grafted

with polar vinyl monomers, such as methyl methacrylate(MMA)

and maleic anhydride. The results of grafting on the EB and

PB copolymers with low butadiene content are shown in Table

6. The EPB terpolymers with adequate butadiene units can be

efficiently vulcanized with the conventional sulfur-based

systems to improve the mechanical properties. It is probably

useful for preparing some kind of gaseous separate membranes.

Table 6 Chemical graft on the EB and PB copolymers*

Sample Bd mol% monomer grafting degree (wt%)

homopolymer PE MMA 2

cop0 1 ymer

EB 5

5

PB 8

8

MMA maleic anhydride

MMA

maleic anhydride

55

1 9

38

11

* Initiator: BPO; solvent: toluene. REFERENCES

1. J.Jr.Boor, "Ziegler-Natta Catalysts and Polymerization",

Academic Press, New York, 1979, p 563, and

references therein.

20. TerpolymekariOn of Olefins with Supported Ti Catalyst 261

2. 3.

4.

5.

6.

7.

8.

9. 1 0 .

11.

1 2 . 13.

1 4 .

15.

16.

J.Furukawa, Angew. Makromol. Chem., 23, 1 8 9 ( 1 9 7 2 ) . J . C u c i n e l l a , A.D.Chirico, a n d A.Mazzei , Eur . Polym. J., - 1 2 , 6 5 ( 1 9 7 6 ) . M.Bruzzone, A.Carbonaro , and C.Corna, Makromol . Chem., - 179 , 21 7 3 ( 1 9 7 8 ) . P . G a l l i , L . L u c i a n i , and G.Cecchin , Angew. Makromol . Chem., 94, 63(1981 1 .

J .C. W.Chien, J .C. Wu, a n d I. J .Kuo, J . P o l y m e r S c i . , Polymer Chem. Ed., 20, 2091(1982) . K.Soga, J . S h i o n o , and Y . D o i , Makromol. Chem., 189,

1531 ( 1 9 8 8 ) . P.J.T.Tait, G.W.Downs, and A.A.Akinbami, A C S Mee t ing , Akron, 1986. D . C . C a l a b r o , and F.Y.Lo, ACS Meet ing , Akron, 1986.

T . T s u t s u i , a n d N . K a s h i w a , P o l y m . Commun., 29,

T.Ke i i , K.Soga, and N.Sa ik i , J . P o l y m e r Sci. , =, 180( 1988 1.

1507 ( 1 9 6 7 ) . M.Fineman, and S.D.Ross, J. Polymer Sci.,?, 2 5 9 ( 1 9 5 0 ) . D . M . G r a n t , and E.G.Pau1, J.Am.Chem.Soc., 8 6 , 2 9 8 4 ( 1 9 6 4 ) .

G . G a t t i , a n d A . C a r b o n a r o , M a k r o m o l . Chem., l72, 1627( 1 9 7 4 ) . K.Soga, T.Sano, R . O h n i s h i , T.Kawata, K . I s h i i , T .Sh iono , a n d Y . D o i , " C a t a l y t i c P o l y m e r i z a t i o n o f O l e f i n s " , E l s e v i e r , Tokyo, 1986, p 109. J.K.Sti l l e , " I n t r o d u c t i o n t o Polymer Chemis t ry" , W i l e y , 1962, p 185.


263

2 1. Kinetics of Ethylene - Propylene Copolymerization over MgC12 -Supported Catalysts

S.K.IHM, K.S.KANG, K.J.CHU and H.S.CHANG

Department of Chemical Engineering, Korea Advanced Institute

of Science and Technology, P.O.Box 131 Cheongryang, Seoul,

Korea

Introduction

The monomer reactivities in a particular polymerization reaction can be obtained

by measuring their reactivity ratios in copolymerization reactions. These reactivity

ratios are calculated from the correlation between the monomer compositions of the

feed and of the product copolymer. However, it is very difficult t o keep a constant

monomer concentration in the reacting phase during the copolymerization reaction.

Therefore, the continuously-purged copolymerization( CPC) system has been often

used to maintain a constant monomer concentration, where the mixture of ethylene

and propylene was continuously supplied under a total pressure of 1 atm. It is

believed that the stopped-flow copolymerization( SFC) system, which was

previously used by Keii et al.') and then modified by Terano et aL2) for propylene

polymerization, can be applied t o observe a quasi-living polymerization state( below

1.0 sec) of ethylene-propylene copolymerization. The present communicat ion

reports some preliminary data concerning the instantaneous values of reactivity

ratio obtained from the SFC system, which are to be compared with the average

values of reactivity ratio obtained from the CPC system.

264 S. K. Ihm, K. S. Kang, K. J. Chu and H. S. Chang

Experimental Part

Catalyst preparation

The MgClz-mpported catalyst used in this study was prepared by coginding

9.522g of anhydrous MgClz with 1.1 ml of Tic14 and 1.201111 of ethyl benzoate(EB)

(EB/MgC12 mole ratio = 0.085) in a Fritsch Pulverisette ball mill. (capacity:45ml;

with five balls of 1.5cm diameter and three balls of 1.2cm diameter) at room

temperature for 2hr. The catalyst with BET surface area of 9m2/g contained 3.80

wt% of titanium.

Copolymer izat ion

1) St opped-flow copolymerization( SFC)

The polymerization apparatus used in this study is similar to the one reported by

Keii et al.')and then modified by Terano et aL2) for propylene polymerization. It

consists of two flasks: One flask(A) contains 200 cm3 of catalyst suspension in

heptane and the other(B) contains 200 ,3313 of Al(C2H5)s dissolved in propylene-

saturated heptane. A water bath is equipped for each container to maintain the

system at a constant temperature. The catalyst suspension in (A) was kept under

nitrogen, because the contact of the catalysts used in the present study with

ethylene or propylene causes cationic polymerisation which proceeds without

Al(C*H&. By applying a small pressure of nitrogen, the solutions in (A) and (B)

are forced to flow out simultaneously through a teflon tube of 2 mm inner diameter.

When the solutions meet at a simple three-necked joint(a), polymerization starts

and continues until quenched by 400 cmJ of ethanol contained in 1 dms flask(C).

The polymerization was conducted at 30.C under a pressure of 1 atm with 0.5g of

21. Olefin Copolymerirath with MsCr, Supported Cutahst 265

catalyst and the prescribed amount of Al(C2Hs)s(Al/Ti mole ratio=5). The

ethylene and propylene concentration was listed in Table 1. The polymerization

time was 0.76 sec. Monomer conversions were found to be below 10 % under the

present conditions. To the polymer suspension in ethanol, 400 cms of water

together with 20 cm3 of HC1 was added and stirred overnight. This was found to

eliminate the catalyst residue in the product. After separating the polymer using

the separatory funnel, it was dried in vacuum a t 1000C.

2) Continuously purged copolymerization(CPC)

The polymerization procedure is similar to the one previously used by Soga et

Copolymerization of ethylene with propylene was carried out in 250 cm3 glass

reactor equipped with a magnetic stirrer. 0.lg of catalyst was suspended in 96 cms

of heptane under nitrogen atmosphere. After the temperature was raised up t o

300C, a mixture of ethylene and propylene was introduced a t a flux of 2 I/min to

assure a constant monomer concentration in the reacting phase into the reactor.

After 10 min, the prescribed amount of AI(CzHb)s(4 cm3 of heptane solution) was

added t o start the copolymerization. The mixture of ethylene and propylene was

continuously supplied under a total pressure of 1 atm. The mole ratio of ethylene t o

propylene was changed by controlling the flow rate of each monomer. T h e

concentrations of ethylene and propylene in heptane were calculated according t o

the vapor-liquid equilibrium using C h a d e a d e r correlation . T h e

copolymerization was conducted a t 3oOC for 10 min and terminated by adding a

dilute hydrochloric' acid solution in ethanol. The product polymer was adequately

washed with methanol and dried in vacuum.

4 )


Polymer Characterization

The compositions of poly(ethylene-x+propylene) were estimated from the A, 2s

/A6 .85p absorbance ratios5) of the IR spectrum(with a Bomem MB-102 Infrared

Spectrophotometer). The calibration curve for the absorbance ratios was obtained

by using polypropylene-polyethylene blends dissolved in xylene.

The melting point of the copolymer was determined from the peak of the

differential scanning calorimetric( DSC) spectra, measured with a Dupont apparatus.

DSC measurements were made at a heating rate of l@C/min. The amples were

melted at 2OOoC.

Results and Dkuasion

Two types of copolymerization, SFC and CPC, were carried out at 300C with the

catalyst system, MgC12/TiCl,/EB/Al( C ~ H S ) ~ . For reference, homopolymerization

of each olefin was conducted under similar conditions. The monomer reactivity

ratios rE and rp(E = ethylene, P = propylene) were calculated according to the

Finernan-Roes method and Kelen-Tiidb met hod6), where the necessary parameters

are defined as follows; ([mEl/[mpl-l '[MEl/[Mpl

G = ImJ4J/LmpJ

= ( [MEl/[M~)2/([mE~/[mpl)

where,

[ M ~ ] w = C o n c . of propene in heptane

Conc. of ethylene in heptane

im*] amount of ethylene in cop01 ymer Im,l= amount of propene in copolym e r

21. Okfin Copolymerization with MgC12 Suppmlpd Cotalyst 267

Fineman-Ross eq.

G = -rp + r E - F

Kelen-Tudos eq.

G/(F+a) = (-rp/a) t (rEtrp/Q)(F/(FtQ))

where a = (Fm,n*Fmax)’’z

The results of two types of copolymerization are summarized in Table 1 3 .

Table 1 shows the monomer concentration in the reacting medium and the

propylene contents of the copolymer produced in the stopped-flow

copolymerization( SFC) of ethylene and propylene together with the evaluation of

some parameters for both Fineman-Ross and Kelen-Tiidas plots. Table 3. shows

the results of the CPC for comparison with those of SFC in Table 1 under the

similar conditions(AI/Ti = 6). The SFC gave the copolymers having slightly’higher

propylene unit contents at the same ethylene/propylene feed ratio than the CPC.

In Table 1, homopolymerization rate constants ,TEE and rpp, could have been

obtained from the SFC yield by measuring the number average molecular weight,

lCfn. Our experiments carried out below 10% conversions did not produce the

accurate and reproducible values of SFC yields due to the difficulty in separating

small amount of products. Table 3 shows the results of the CPC when Al/Ti mole

ratio is 30. This is to clarify the effect of AI/Ti mole ratio on the copolymerization

characteristics in comparison with those in Table 2. The yield was strongly

dependent upon the ratio of AI(C2H5) to titanium as to be shown later on in Fig. 3.

It can be seen that the propylene content in the copolymer at AI/Ti=30 is slightly

larger than at AI/Ti=5.

Using the parameters of F, G and Q in Table 1-3, both Fineman-Ross and

Kelen-Tud8s plots for the two types of copolymerizations are given in Fig. 1-2. The

monomer reactivity ratios calculated from these plots are listed in Table 4.

Good linearity w a s obtained for Fineman-Ross plots as well as Kelen-TiidGs plots.

Both plotting methods provided almost the same reactivity ratios. The propylene

reactivity ratio r in SFC is about two times larger than that in CF’C. This is P

268 S . K. Ihm, K. S. Kang, K. J. Chu and H. S . Chang

expected because the propylene content in the copolymer is higher in SFC than in

CPC for the same feed cornposition as shown in Table 1-3. It is of interest to note

in the Table 4 that the value(3.64) of rgxrp for the SFC was higher than that (3.57

for AI/Ti=5) for CPC, and also the value(3.57) for Al/Ti=5 was higher than

that(2.1) for AI/Ti=30 in CPC. Thus the distribution of the ethylene and

propylene monomer units is expected to be more blocky for the SFC than for the

CPC7).

The yield was strongly dependent upon the ratio of AI(C2Hs)s to titanium as

shown in Fig. 3. It is often observed in ethylene polymerization using Ziegler-Natta

catalysts that addition of a small quantity of propylene monomer markedly

increases the apparent polymerization activity. The results are often explained by

the assumption that the propagation rate constants of the cross reactions are very

high8). On the other hand, the increased rates of ethylene polymerization might be

explained by an increase of monomer diffusion through less crystalline copolymer

film due to incorporation of comonomer as described by Soga et al.’) From Fig. 3.,

it is shown that the apparent polymerization activity shows a maximum. It is

recognized that the polymerization activity, or more precisely, the propagation rate,

of ethylene is much higher than that of propylene. However, the ethylene activity

was not so much high for AI/Ti=5 and slightly higher for AI/Ti=30 than the

propylene activity. It is expected that as AI/Ti mole ratio increases, the ethylene

activity becomes higher than the propylene activity and the maximum activity will

shift to the lower range of comonomer content.

The values of the heat of fusionpHt and the melting point, T, for the copolymers

shown in Fig. 4. and Fig. 5. are very typical for ethylene copolymers in this

composition range. Their values in SFC was always higher than those in CPC.

That is to say, the crystallinity of the copolymer obtained by SFC was always larger

than those obtained by CPC for the same comonomer content in the copolymer. It

is expected that the crystallinity be smaller for higher comonomer content in the

copolymer. But the crystallinity will be affected by various factors, such as the

21. Olefin CoporVlneriurrion with MgC12 Supported Gztu!vst 269

comonomer distribution and its configuration in the copolymer chain as well as its

content. The above experimental results might be well explained as the following

bases12). The nature of active sites in heterogeneous Ziegler-Natta catalyst is

essentially not uniform. These active sites might be largely classified to three kinds

of sites, that is, isospecific titanium(II1) site, aspecific titanium(II1) site and

ethylene-favorable titanium(I1) site. In the SFC with low AI/Ti mole ratio, there

might exist only the isospecific site which polymerizes olefins to The stereospecific,

highly crystalline copolymer. But in the CPC there might exist large amount of

ethylene-favorable titanium(I1) site as well as titanium(II1j sites. And also as

AI/Ti mole ratio increases, the isospecific titanium(II1) sites might be transformed

to the aspecific titanium(II1) sites due to the extraction of ethyl benzoate by

AI(C*H5)3. Aspecific site is well known to be more favorable to the incorporation of

comonomer into the polymer chain than isospecific site.

Acknowledgement

This work has been partly supported by the research grant from Central

Research Center of Han-Yang Chemical Corporation.

References

1. T. Keii, M. Terano, K. Kimura and K. Ishii, Makromol. Chem., Rapid Commun.

8, 583-587( 1987)

2. M. Terano and T. Kataoka, Makromol. Chem. 190,97-102(1989)

3. K. Soga, H. Yanagihara and D. Lee, Makromol. Chem. 190, 3744(1989)

4. K.C. Chao and J.D. Seader, AICHE J., 7,5%-605(1961)

5. C. Tosi and T. Simonazzi, Angew. Makromol. Chem. 32, 1&161( 1973)

6. T. Kelen and F. Tiid&, J . Makromol. Sci.-Chem., A9(1), 1-27(1975)

270 S. K. Ihm, K. S. Kang, K. J. Chu and €I. S. Chang

7. N. Kashiwq A. Mizuno and S. Minami, Polymer Bulletin 12, 105-109(1984)

8. V. Busico, P. Corradini, A. Ferraro and A. Proto, Makromol. Chem. 187,

1125-1130( 1986)

9. K. Soga, H. Yanagihara and D. Lee, Makromol. Chern. 190,995-1006(1989)

10. P. Locatelli, M. C. Sacchi, I. Tritto and G. Zannoni, Makromol. Chem., Rapid

Commun. 9,57540(1988)

11. .J.P. Luongo, J . Appl. Polymer Sci., 3, 302(1960)

12. K.S. Kang, Ph.D. Dissertation, Korea Advanced Institute of Science and

Technology (1989)

Table 1. Results of the stopped-flow copolymerization of ethylene and propylene together with the evaluation of some parameters'

Conc. of monomer in heptane P in copolymerb [ME] ,mo1/1 [Mpl ,~ol/l mol-X G F G/(F+a) F/(F+a)

0.0602 0.0067 1.156 8.896 0.947 7.532 0.783 0.0582 0.0147 3.014 3.876 0.497 5.100 0.654 0.0565 0.0242 4.569 2.222 0.261 4.240 0.498 0.0540 0.0360 6.943 1.388 0.168 3.220 0.390 0.0508 0.0509 11.268 0.873 0.127 2.238 0.326 0.0467 0.0701 14.252 0.556 0.098 1.540 0.271 0.0412 0.0962 20.124 0.321 0.073 0.955 0.217

0.0622 - - 0.2889 Isotacticityc = n.d.(by extraction), above 95X(by IR)

a Copolymerization conditions: Catalyst = 0.5g, Al/Ti = 5 mole ratio; each vol. of heptane = 200cn3; Total pressure latn; T = 30T; t = 0.76sec; E and P denote ethylene and propylene respectively. Calculated from I R spectra of copolymers. Isotacticity of polypropylene is defined by the fraction insoluble in boiling n-heptane for 6 hr and determined by A~r4/Agg5 absorbance ratio of IR spectra,

respectively1 1 .

Table 2. Results of the continuously-purged copolymerization of ethylene and propylene together with the evaluation of some parameters(Al/Ti=5)"

Conc. of monomer in heptane Yield P in copolymerb [ME I , m o W 4 1 , m o W in g mol-X G F G/(F+a) F/(F+a)

0.1204 0.0134 0.276 0.464 8.943 0.527 13.536 0.7976 0.1170 0.0293 0.583 1.410 3.943 0.229 10.871 0.6314 0.1129 0.0484 0.714 2.634 2.270 0.147 8.087 0.5237 0.1079 0.0719 1.003 4.082 1.436 0.0958 6.257 0.4174 0.1016 0.1017 1.908 5.550 0.941 0.0588 4.888 0,3055 0.0934 0.1401 2.111 10,158 0.591 0.0503 3.212 0.2734 0.0824 0.1923 2.189 15.595 0.349 0.0339 2.082 0.2023

0.1243 - 0.092 - 0.5777 0.736 IsotacticityC = 70.9X(by extraction), 83.OX(by IR)

a Copolymerization conditions: Catalyst = 0.18, Al/Ti = 5 mole ratio; each vol. of heptane = lOOcm3; Total pressure = lata; T = 3OOC; t = 10min; E arid P denote ethylene and propylene respectively. Calculated from IR spectra of copolymers. Isotacticity of polypropylene is defined by the fraction insoluble in boiling n-heptane for 6 hr and determined by Ag7,/Agg, absorbance ratio of IR spectra, respectivelyll.

N r

N Y

N

h3

Table 3. Results of the continuously-purged copolymerization of ethylene and propylene together with the evaluation of some parameters(Al/Ti=30)a

Conc. of monomer in heptane Yield P in copolymerb [%I ,mol/l [$I ,mol/l in g mol-% G F G/(F+a) F/( Fta)

0.1204 0.1170 0.1129 0.1079 0.1016 0.0934 0.0824

0.0134 0.0293 0.0484 0.0719 0.1017 0.1401 0.1923

0.712 0.780 8.930 0.6372 11.460 0.818 1.570 1.748 3.929 0.2846 9.210 0.667 4.822 3.252 2.254 0.1828 6.940 0.563 5.276 5.268 1.417 0.1251 5.305 0.468 3.884 6.398 0.932 0.0684 4.430 0.325 2.616 9.06 0.600 0.0443 3.221 0.238 1.827 14.67 0.355 0.0316 2.045 0.182

0.1243 - -

0.5777 0.560 1.780 Isotacticityc = 63.7X(by extraction), 73%( IR)

~ ~ ~~ ~ ~~~~~~~~~

a Copolymerization conditions: Catalyst = O.lg, Al/Ti 30 mole ratio; each vol. of heptane = 100cm3; Total pressure = latm; T = 30%; t = l0min; E and P denote ethylene and propylene respectively.

Isotacticitg of polypropylene is defined by the fraction insoluble in boiling n-heptane for 6 hr and determined by A g T r / A g g 5 absorbance ratio of IR spectra, respectivelyll.

b Calculated from IR spectra of copolymers.

21. Olefin CopolVrnertarion with MgCh Sugpotkd Gztolyst 273

Table 4. Evaluation of monomer reactivity ratios

Type of E r 'P

Polymerization Fineman-Ross Kelen-Tbd6s Fineman-Ross Kelen-Tud6s

Stopped-flow copolymn 9.6 9.4 0.38 0.33 Continuously- purged copolymna (a) 17.4 17 .6 0 . 2 1 0.23

(b) 14.2 13.7 0.15 0.075

a (a) For Al/Ti=5 and (b) For Al/Ti=30

G

-2 J 0 0.2 0.4 0.6 0.8 1

F Fig. 1. Fineman-Ross lots for eth lene-propylene co ymerisation

: o ; for SFC, * ; !or CPC(Al/Ti-S), + ; for CP r' (AI/Ti=30).


1s-

12.-

0 0.2 0.4 0.6 0.1 1

F/(F+Q) Fig. 2. Kelen-Tudk plots for eth lene-propvlene ropol mersation

: o ; for SFC, * ; for CPC(Ay/Ti=5), + ; for CPC(AI/Ti=30)

45

a0

2 E 9J eo

10

T

i *

P N

I l l 0

0 I ' H -

0 0.2 0.4 0.6 0.1

Fig. 3. Yield[total polgmrr(g)/amount of monomers dissolved in heptane([E]f[P])] a a function of monomer composition. Polymeridion conditions are the Same M those in Table 2 and Tablc 3, respectively.: o ; fa AI/Tb5,

; for AI/Ti=30, E and P denote ethylene and propylene, respectively.

21. Olefin CopolVmeriurrion with M&12 Supported Gztalyst 275

30.-

9 3. WiF

3

-

Q

10

0 ,

0

0 0

0 .. 0

# + + 0 Y U 0

+ U - -

30.-

9 3. WiF

3

-

Q

10

0 ,

Fig. 4. Heat of fuaion of ?oilmen obtained under the same condition as in Table 1-3 as J function of monomer cornpition: o ; for SFC, * ; for CPC(AI/Ti =5), + ; for CPC(AI/Ti=30).

0

0 0

0 .. 0

# + + 0 Y U 0 h

+ U

t T - -

i t

Fig. 5. Melting point of polymers obtained under the m e condition as in ‘l’ablc 1 3 as a function af monomer composition: o ; for SFC, ; for CPC(XI/Ti =5), + ; for CPC(AI/Ti=N).

0 0.2 0.4 0.8 0.8 1


277

22. A Study on the Active Sites of a Primary Type of MgC12-Sup- ported Catalyst by Ethylene - Propylene Copolymerization

MlNORU TERANO a n d K A Z U H I R O I S H I I Toho T i t a n i u m C o . , L t d . , C h i g a s a k i 3-3-5, C h i g a s a k i 253, J a p a n

ABSTRACT E t h y l e n e - p r o p y l e n e c o p o l y m e r i z a t i o n was c o n d u c t e d u s i n g a p r i m a r y

t y p e o f MgC12-suppor t ed c a t a l y s t . The n a t u r e o f t h e a c t i v e s i t e s o f t h e c a t a l y s t was s t u d i e d f r o m t h e

m i c r o s t r u c t u r e a n d some p h y s i c a l p r o p e r t i e s o f t h e c o p o l y m e r o b t a i n e d by u s i n g t h e c a t a l y s t .

I NTRODUCT I ON

I n t e r n a t i o n a l R e s e a r c h , ” b u t i t was n o t e f f i c i e n t e n o u g h . T h e c a t a l y s t was i m p r o v e d t o a g r e a t e x t e n t b y M o n t e d i s o n 2 ) a n d M i t s u i P e t r o c h e m i c a l . 3 )

h a v e s i n c e b e e n p r o p o s e d a n d much e f f o r t h a s b e e n made t o s t u d y t h e n a t u r e o f t h e c a t a l y s t s . 4 - ’ 6 )

i n t h e p r i m a r y t y p e o f M g C l 2 - s u p p o r t e d c a t a l y s t by t h e r m o g r a v i m e t r y / d i f f e r e n t i a l t h e r m a l a n a l y s i s (TG-DTA) i n c o m b i n a t i o n w i t h o t h e r m e t h o d s , a n d f o u n d t h a t T i c 1 4 a n d EB i n t h e M g C l 2 - s u p p o r t e d c a t a l y s t i n t e r a c t o n l y w i t h MgC12, l e a v i n g no v a c a n t s i t e s o n T i C 1 4 . 1 7 )

MgC12-suppor t ed c a t a l y s t was f u r t h e r s t u d i e d f r o m t h e m i c r o s t r u c t u r e a n d some p h y s i c a l p r o p e r t i e s o f t h e e t h y l e n e - p r o p y l e n e c o p o l y m e r o b t a i n e d by u s i n g t h e c a t a l y s t .

M g C l 2 - s u p p o r t e d Z i e g l e r c a t a l y s t was o r i g i n a l l y d e v e l o p e d by S h e l l

Many t y p e s o f MgC12-suppor t ed c a t a l y s t s f o r p r o p y l e n e p o l y m e r i z a t i o n

R e c e n t l y , we h a v e s t u d i e d t h e s t a t e s o f e t h y l b e n z o a t e (EB) a n d T i C 1 4

I n t h i s p a p e r , t h e n a t u r e o f t h e a c t i v e s i t e s o f t h e p r i m a r y t y p e o f

EXPER IMENTAL (REAGENTS)

E x t r a p u r e h e p t a n e ( f r o m Toa O i l C o . , L t d . ) a n d EB ( f r o m K a n t o C h e m i c a l Co. , L t d . ) w e r e u s e d a f t e r p a s s i n g t h r o u g h a m o l e c u l a r s i e v e

278 M. Terano and K. Ishii

4-A c o l u m n . A n h y d r o u s MgC12 (Toho T i t a n i u m C o . , L t d . , s p e c i f i c s u r f a c e a r e a : l l m 2 / g ) a n d T i C 1 4 (Toho T i t a n i u m C o . , L t d . ) w e r e u s e d w i t h o u t f u r t h e r p u r i f i c a t i o n .

(PREPARATION)

h e p t a n e a n d 0 . 1 0 mol o f EB a t 40°C u n d e r n i t r o g e n , f o l l o w e d by t h e d r o p w i s e a d d i t i o n o f 0 . 1 0 mol o f T i C 1 4 . A f t e r t h e r e a c t i o n a t 40°C f o r l h , a y e l l o w i s h s o l i d p r o d u c t was s e p a r a t e d by f i l t r a t i o n , w a s h e d w i t h h e p t a n e a n d d r i e d i . v a c . The m o l e r a t i o o f T i C l d / E B i n t h e r e s u l t i n g c o m p l e x was f o u n d t o b e 1.09.

e a c h compound w e r e p l a c e d i n a 1 L s t a i n l e s s s t e e l v i b r a t i o n m i l l p o t w i t h 50 b a l l s ( d i a m e t e r 25mm) u n d e r n i t r o g e n a n d v i b r a t e d a t room t e m p e f a t u r e .

t h e T i C 1 4 - E B c o m p l e x w e r e m i x e d o r c o g r o u n d a s d e s c r i b e d a b o v e ; n i n d i c a t e s t h e c o g r i n d i n g t i m e i n h o u r s .

T iC14 .EB c o m p l e x : I n a 200ml g l a s s f l a s k w e r e p l a c e d 80ml o f

G r i n d i n g : 315mmol (30g) o f t h e M g C l 2 a n d t h e p r e s c r i b e d a m o u n t o f

C a t a l y s t s (Cat -An) : 315mmol ( 3 0 g ) o f t h e MgC12 a n d 1 5 . 4 g (45mmol) o f

(COPOLYMER I ZATION)

s t e e l a u t o c l a v e a t 60°C f o r 15 m i n u t e s u n d e r a c o n s t a n t p r e s s u r e o f 1 a t m w i t h 8.5mmol o f A l (CZH6)3 , t h e p r e s c r i b e d a m o u n t o f c a t a l y s t ( c a t a l y s t w e i g h t : 2 . 0 - 3 . 0 9 , A l / T i m o l e r a t i o : 30 -40) a n d IL o f h e p t a n e .

e a c h ) .

E t h y l e n e - p r o p y l e n e c o p o l y m e r i z a t i o n was c o n d u c t e d i n a 2L s t a i n l e s s

F low r a t e o f e t h y l e n e - p r o p y l e n e m i x e d g a s was rl.OL/min ( 2 . 0 L / m i n

The p o l y m e r o b t a i n e d was w a s h e d w i t h e t h a n o l a n d d r i e d i . v a c .

(MEASUREMENT)

t h e c o p o l y m e r w e r e c a l c u l a t e d f r o m NMR a n a l y s i s (JEOL GSX-270 ; n / 4 p u l s e o f 7 . 5 ~ ~ , 6 . 8 s r e p e t i t i o n r a t e ) .

by GPC ( W a t e r s ALC/GPC 1 5 0 C , S h o d e x AD-807/S, AT-IOMS, a n d AD-803s

P r o p y l e n e c o n t e n t , random i n d e x a n d monomer t r i a d d i s t r i b u t i o n o f

A v e r a g e m o l e c u l a r w e i g h t o f t h e c o p o l y m e r p r o d u c e d was m e a s u r e d

22. CopolymniUrrior! with MsCr, Supported Catalyst 279

c o l u m n s ) a t 140°C u s i n g o - d i c h l o r o b e n z e n e a s a s o l v e n t .

f u s i o n ( A H f ) o f t h e c o p o l y m e r were m e a s u r e d by DSC (Mac S c i e n c e DSC- 3100) a t a h e a t i n g r a t e o f ZO”C/min u s i n g a-A1203 a s a r e f e r e n c e .

G l a s s t r a n s i t i o n t e m p e r a t u r e ( T g ) , m e l t i n g p o i n t (Tin), a n d h e a t o f

RESULTS AND DISCUSS I ON

s t a t e s o f EB a n d T iC14 i n t h e MgC12-suppor t ed c a t a l y s t s i n c o m b i n a t w i t h i n f r a r e d s p e c t r o s c o p y , a n d i t was f o u n d t h a t : 0 T i C 1 4 , E B c o m p l e x d e c o m p o s e s by g r i n d i n g w i t h MgC12, on w h i c h T i c

0 T i c 1 4 d i r e c t l y c o o r d i n a t e d by EB c a n b a r e l y become a c t i v e s i t e s .

I n a p r e v i o u s s t u d y , l ” TG-DTA was a p p l i e d t o i n v e s t i g a t e t h e

EB a r e s u p p o r t e d i n d e p e n d e n t l y .

on

4 a n d

0 I n c r e a s e o f a c t i v i t y w i t h . g r i n d i n g t i m e i s c a u s e d by t h e i n c r e a s e o f

H e r e , we a r e t r y i n g t o o b t a i n f u r t h e r i n f o r m a t i o n a b o u t t h e a c t i v e s i t e s o f MgC12-suppor t ed c a t a l y s t by s t u d y i n g t h e m i c r o s t r u c t u r e o f t h e p o l y m e r p r o d u c e d , w h i c h s e e m s t o r e f l e c t m o s t c l e a r l y t h e d i f f e r e n c e i n t h e s t a t e s o f t h e n a t u r e o f a c t i v e s i t e s .

E t h y l e n e - p r o p y l e n e c o p o l y m e r i z a t i o n was u s e d i n s t e a d o f p r o p y l e n e h o m o p o l y m e r i z a t i o n b e c a u s e o f t h e c l a r i t y o f t h e ‘3C-NMR s p e c t r u m .

The r e l a t i o n s h i p b e t w e e n c a t a l y s t a c t i v i t y a n d g r i n d i n g t i m e i s shown i n F i g u r e 1 . The a c t i v i t y i m p r o v e d r e m a r k a b l y e v e n by a s h o r t p e r i o d o f g r i n d i n g , t h e n i n c r e a s e d l i n e a r l y . T h i s r e s u l t i s c o n s i s t e n t w i t h t h a t f o r p r o p y l e n e h o m o p o l y m e r i z a t i o n r e p o r t e d e a r l i e r . I 7 )

T a k i n g p r e v i o u s r e s u l t s i n t o c o n s i d e r a t i o n , i t i s p o s s i b l e t h a t a c t i v e s i t e s f o r e t h y l e n e - p r o p y l e n e c o p o l y m e r i z a t i o n i s p r o d u c e d by g r i n d i n g T i c 1 4 .EB c o m p l e x w i t h MgC12.

T a b l e 1 shows t h e monomer t r i a d d i s t r i b u t i o n i n t h e c o p o l y m e r c a l c u l a t e d f r o m 13C-NMR. The c o p o l y m e r s o b t a i n e d u s i n g Cat-As - Cat-A38 a r e a l m o s t i d e n t i c a l , b u t t h e c o p o l y m e r p r o d u c e d b y Cat-A0 i s q u i t e d i f f e r e n t f r o m t h e o t h e r s . I n p a r t i c u l a r , t h e v e r y low v a l u e o f

“PPP” a n d h i g h v a l u e o f “EEE” i n d i c a t e t h e p r o p e r t y o f a c t i v e s i t e s i n Ca t -An , w h i c h a r e much more s u i t a b l e f o r e t h y l e n e p o l y m e r i z a t i o n t h a n f o r p r o p y l e n e p o l y m e r i z a t i o n

a c t i v e s i t e s .


n .r( * I M

2 W 6 h

0 a I M U

h +J .r(

4

> .r(

+J 0 4

3000 I

l o o o I f,

0 1 0 20 30 G r i n d i n g t i m e [ h l

F i g u r e 1 . R e l a t i o n s h i p b e t w e e n a c t i v i t y a n d g r i n d ng t i m e

P r o p y l e n e c o n t e n t s a n d r andom i n d e x ( PPE + EEP + EPE + PEP ) o f t h e c o p o l y m e r s w e r e c a l c u l a t e d f r o m t h e r e s u l t s i n T a b l e 1 a n d p l o t t e d i n F i g u r e s 2 a n d 3 . T h e s e f a c t o r s h a v e t h e same t e n d e n c y , t h a t i s , v e r y low v a l u e s w e r e o b t a i n e d f o r Cat-Ae b u t i n c r e a s e d d r a m a t i c a l l y f o r Cat-As a n d r e m a i n e d c o n s t a n t f o r C a t - A g - C a t - A a ~ .

I t may b e u n d e r s t o o d f r o m t h e r e s u l t s t h a t t h e c a t a l y s t s wi th v a r i o u s c o g r i n d i n g t i m e s , c a n p r o d u c e t h e c o p o l y m e r w i t h t h e same p r o p e r t i e s f o r b o t h p r o p y l e n e c o n t e n t a n d r andom i n d e x . I n o t h e r w o r d s , t h e a c t i v e s i t e s f o r m e d i n t h e c a t a l y s t s i n c r e a s e d w i t h c o g r i n d i n g t i m e b u t t h e p r o p e r t y r e m a i n e d c o n s t a n t .

Some a n a l y t i c a l d a t a o f c o p o l y m e r s o b t a i n e d u s i n g Cat-A0 - Cat -AaO a r e s u m m a r i z e d i n T a b l e 2 . N o c l e a r d i f f e r e n c e c a n b e o b s e r v e d i n Tg a n d Tm, b u t A H f a s w e l l a s fi a n d i& shows t h e same t e n d e n c y f o u n d in p r o p y l e n e c o n t e n t a n d r andom i n d e x , w h i c h a g r e e s w i t h t h e p r e v i o u s d i s c u s s i o n .

Table 1 . Triad distribution in ethylene-propylene copolymer

Cat a lys t Gr ind ing triad distribution [mol%] No. time

Chl PPP EEE PPE PEE EPE PEP

A0 0 2 49 11 15 18 5 A6 5 17 2 5 23 15 1 0 1 0 A 1 0 10 16 24 21 16 11 12

A 3 0 30 18 2 5 17 17 12 11 A 1 6 15 19 2 1 19 21 1 0 10

n 5 0

U

e E 0) c, c 0

E

0

0)

E 0)

x a 0 c a

+

6o I m = -

301 20 0 10 20 30

Grinding time Chl

Figure 2 . Relationship between propylene content and grinding time


6 0

50 I

4 0

n z 0 E U

x 0, V c I

E 0 V c m w

- m

8 8

-

-

-

- I I I

F i g u r e 3 . R e l a t i o n s h i p b e t w e e n r a n d o m i n d e x a n d g r i n d i n g t i m e

T a b l e 2 . DSC a n d GPC d a t a o f e t h y l e n e - p r o p y l e n e c o p o l y m e r

- - C a t a l y s t G r i n d i n g Tg T m AHf M n M w

No. t i m e C h l ["Cl ["cI C c a l / g l (x104) ( ~ 1 0 ~ )

Ae 0 - 5 9 . 4 1 1 8 . 1 3 . 4 3 1 . 3 2 1 1 . 3 A6 5 - 5 9 . 6 1 1 6 . 8 1 . 4 0 0 . 7 4 9 . 6 A 1 E 1 0 - 5 6 . 2 1 1 8 . 2 0 . 7 5 8 . 0 A 1 5 15 - 5 5 . 9 1 1 8 . 3 1 . 7 3 0 . 6 7 5 . 3 A3 0 30 - 5 5 . 8 1 1 6 . 7 1 . 7 2 0 . 5 0 6 . 4

-

22. Copolymehtim with MBcr, Supported Catalyst 283

From a l l t h e r e s u l t s a b o v e , we may a r r i v e a t t h e c o n c l u s i o n t h a t 0 A c t i v e s i t e s f o r e t h y l e n e - p r o p y l e n e c o p o l y m e r i z a t i o n w e r e p r o d u c e d by

t h e d e c o m p o s i t i o n o f T i C 1 4 . E B c o m p l e x in t h e c o g r i n d i n g p r o c e s s w i t h MgC12.

0 I n c r e a s e o f a c t i v i t y i s c a u s e d by t h e i n c r e a s e o f t h e same t y p e o f a c t i v e s i t e s .

REFERENCES 1 J a p . 4 3 2 5 3 3 ( 1 9 6 4 ) , S h e l l , i n v s . W . A . H e w e t t , E . C . S h o k a l 2 J a p . 1 0 7 6 2 0 1 ( 1 9 8 1 1 , M o n t e d i s o n SPA, i n v s . : U . G i a n n i n i , A . C a s s a t a ,

3 J a p . 1 0 1 4 4 7 1 ( 1 9 8 1 ) , Mitsui P e t r o c h e m i c a l , i n v s . : A . T o y o t a ,

4 J . C. W . C h i e n , J . T . T . H s i e h , J . P o l y m . Chem. E d . 1 4 , 1 9 1 5 ( 1 9 7 6 ) 5 A . M u n o z - E s c a l o n a , J . V i l l a l b a , P o l y m e r 1 8 , 179 (1977) 6 K . S o g a , M. T e r a n o , S . I k e d a , P o l y m . B u l l . ( B e r l i n ) 1 , 8 4 9 ( 1 9 7 9 ) 7 E . S u z u k i , M. T a m u r a , Y . D o i , T . K e i i , Makromol . Chem. 1 8 0 , 2 2 3 5

8 N . K a s h i w a , P o l y m . J . 1 2 , 6 0 3 ( 1 9 8 0 ) 9 P . G a l l i , L. L u c i a n i , G . C e c c h i n , Angew. M a k r o m o l . Chem. 9 4 , 6 3

1 0 S . A . S e r g e e v , G . D . B u k a t o v , E . M. M o r o z , V . A . Z a k h a r o v , R e a c t .

11 T . K e i i , M a k r o m o l . Chem. 1 8 3 , 2 2 8 5 ( 1 9 8 2 ) 1 2 N . F . B r o c k m e i e r , J . B. R o g a n , I n d . E n g . Chem. P r o d . R e s . Dev . 2 4 ,

1 3 R . S p i t z , P . M a s s o n , C . B o b i c h o n , A . G u y o t , Makromol . Chem. 1 8 9 , 1 0 4 3

1 4 L . A b i s , E . A l b i z z a t i , U. G i a n n i n i , C . G i u n c h i , E . S a n t o r o ,

1 5 C . P r o s t , G . Nemoz, A . M i c h e l , M a k r o m o l , Chem. , M a c r o m o l . S y m p . 2 3 ,

1 6 K . S o g a , T . U o z u m i , H . Y a n a g i h a r a , Makromol . Chem. 1 9 0 , 31 ( 1 9 8 9 ) 1 7 f o r e x a m p l e , M. T e r a n o , T. K a t a o k a , T . K e i i , M a k r o m o l . Chem. 1 8 8 ,

P . L o n g i , R . M a z z o c h i

N. K a s h i w a

( 1 9 7 9 )

( 1 9 8 1 )

K i n e t . C a t a l . L e t t . 2 1 , 4 0 3 ( 1 9 8 2 )

2 7 8 ( 1 9 8 5 )

( 1 9 8 8 )

L. N o r i s t i , M a k r o m o l . Chem. 1 8 9 , 1 5 9 5 ( 1 9 8 8 )

1 6 1 ( 1 9 8 9 )

1 4 7 7 ( 1 9 8 7 )


285

23. Syntheses of Terminally Hydroxylated Polyolefins Using Zn(C2H5)2 and Oxygen as Chain Transfer and Quenching Reagents

T.SHION0, K.YOSHIDA and K.SOGA

Research Laboratory of Resources Utilization, Tokyo Institute of

Technology, 4259 Nagatsuta, Midori-ku, Yokohama 227, Japan

ABSTRACT

Propene and 1-hexene were polymerized with the conventional

TiC13-A1(C2H5)2C1 catalyst in the presence of ZII(C~H,=)~ as chain

transfer reagent. The produced Zn-polymer bonds were reacted with

oxygen gas followed by hydrolysis, which produced corresponding

terminally hydroxylated polyolefins in a fairly good yield.

INTRODUCTION

Many kinds of plastics and elastomers are commercially

produced by using Ziegler-Natta catalysts. Ziegler-Natta

catalysts have been dramatically improved both in activity and

stereospecificity, yielding new generations of highly economical

production systems. Much effort is recently being made to

functionalize these polyolefins. Terminally functionalized

polymers are expected to be useful not only to synthesize block

copolymers but also to modify polymer properties. A method for

synthesizing terminally functionalized polypropylene using the

living V ( ~ C ~ C ) ~ / A ~ ( C ~ H ~

al.’) This system can,

propylene. On the other

tional TiC13/A1(C2H5)2C1

as well as olefin copol!

2C1 system has been reported by Doi et

however, give only syndiotactic poly-

hand, it is well known that the conven-

catalyst produces isotactic polyolefins

mers. The mean life time of the living

polymer chains in this catalyst system is relatively long.2) In

addition, Zn(C2H5I2 reduces the molecular weight of polymers very

ef fe~tively.~) Therefore, the Zn-polymer bonds are expected to

be formed in higher concentration by applying this system. From

286 T. Shiono, K. Yoshida and K. Soga

such a viewpoint, an attempt was made to prepare terminally

functionalized polyolefins by using the TiCl3/A1(C2H5I3

/Zn(C2H5I2 catalyst.

EXPERIMENTAL

Materials: Propene (Mitsubishi Petrochemical Co.) was

purified by passing through columns of CaC12, P2O5 and molecular

sieves 3A. 1-Hexene was refluxed over CaH2 and distilled before

use. TiC13 (AA type, Toho Titanium Co.), A1(C2H5)2C1 and

(Tosoh Akzo Chemical Co.) were used without further

purification. Research grade heptane (commercially obtained) was

purified according to the usual procedures. Nitrogen of 99.9995%

and oxygen of 99.7% (Nihon Sanso Co.) was used after passing

through a 3A molecular sieve column.

Preparation of polymer samples: Propene polymerization was

conducted with a 0.05 dm3 stainless steel autoclave equipped with

a magnetic stirrer. After measured amounts of heptane, TiC13,

A1(C2H5I2C1 and Zn(C2H5)2 were added into the reactor under

nitrogen atmosphere, 3 dm3(S.T.P.) of propene monomer was

condensed into the reactor at liquid nitrogen temperature. Poly-

merization was performed at 4OOC. The reaction mixture was

then brought into contact with oxygen gas at room temperature for

10-20 min followed by the addition of a dilute solution of hydre

chloric acid in ethanol. The ethanol soluble polymer was

extracted with hexane followed by evaporation of hexane. Both

the ethanol- soluble and -insoluble polymers were dried i. vac.

at 6OoC for 8 hrs. 1-Hexene polymerization was conducted in a

0.2 dm3 glass reactor in place of a stainless steel autoclave.

Other procedures were almost the same as those used for propene

polymerization.

3C NMR spectra of polymers were

recorded on JEOL EX-90 or GX-270 spectrometer in the pulse

Fourier Transform (FT) mode. The spectra were obtained at room

temperature or 12OoC in 25 s of pulse repetition in CDC13 or

C2D2C14 solution,using hexamethyldisiloxane (HMDS) as an internal

reference (2.03 ppm downfield from tetramethylsilane). The 'H

decoupled distortionless enhancement by polarization transfer

Analytical procedures:

(DEPT) method was used to discriminate methylene resonances from

methyl and methine resonances.

Molecular mass distribution of polymers was recorded on

Shodex LC HT-3 equipped with a Shodex 80M/S column at 14OOC and

o-dichlorobenzene as solvent.

The melting temperature of polypropylene was recorded on

Shimadzu DSC-50. The powder samples of 5 mg were encapsulated in

aluminum pans and heated at 10°C/min up to 2OO0C and kept this

temperature for 5 min (first run). After cooling down to room

temperature, the samples were again heated at 10°C up to 2OOOC

(second run 1.


1-Hexene Polymerization: 1-Hexene polymerization was

performed with various concentrations of Zn(C2H5)2. The results

obtained both in the presence and absence of A1(C2H5)2C1 are

shown in Table 1. The TiC13/Zn(C2H512 catalyst system was found

to be active for the 1-hexene polymerization even in the absence

of A1(C2H5)2C1. The activity of TiC13/A1(C2H512C1 catalyst

system was, however, about 1 0 times higher than that of the

TiC13/Zn(C2H5)2 system. Addition of Zn(C2H5)2 to this system

effectively decreased the molecular weight with a slight decrease

in the polymer yield.

In Table 1 is also shown the result for 02-quenched polymer.

Structure of Poly-I -hexene: To investigate the polymer end

structure, the polymers obtained in the presence of large amounts

of Zn(C2H5)2 were analyzed. Figure 1 shows the 13C NMR spectra of

ethanol soluble polymers (Run nos. Y492 and Y5121, which display

several weak peaks besides six major 13C resonances attributed to

I-hexene units in the main chain. Those resonances of ethanol

soluble polymers can be assigned as indicated in Figure la and

Figure lb. The observed and calculated values of chemical shifts

are summarized in Table 2. The intensities of the methyl (C1) and

ethyl(C6 and C7) are almost equal (see Figure la), which implies

that the living polymer chains were predominantly transferred by

Zn(C2H5I2. On the other hand, the intensities of the peaks

Quenching by oxygen did not change polymer yield significantly.

Table 1 Results of 1-hexene polymerization with the TiCl3/A1(C2HS),Cl/2n(C2H5)2 catalyst system

Run no. TiC13 A11C2H5)2C1 Zn(C2H5)2 Yield [g/mmol-Ti] Quencher Mn Polym. Chain

[nuno11 [mmol/dm3 1 [mmol/dm3 I Ethanol Insol. Ethanol Sol. 1x1 03] [mol/mol-Ti]

Y501 0.70 0 2 0.62 0 e t hano 1 - - Y491 0.87 0 20 1.1 0 e t hano 1 - - Y492 1.02 0 200 0 0.94 ethanol - - Y511 0.75 20 0 7.5 0 ethanol 46 0.00016

Y502 0.58 20 20 4.5 0 et hano 1 2.5 0.00181

Y512 0.97 20 200 0.83 1.19 ethanol - - - - - - - - _ _ _ _ _ _ _ _ _ _ _ _ _ _ - - - - - - - - - - - - - - - - - _ - - - - - - - _ - - - Y521 0.83 20 200 0 1.63 oxygen - -

Polymerization conditions; heptane = 0.040 dm3, 1 -hexene = 3 dm3(S.T.P. 1 , 0.20 dm3 glass reactor,

4OoC, 1 hr.

c, Ca Ca c,

'a

r

a

c7 I

b

1 " " 1 " " 1 " " 1 " ' l " ' ' 1 ' ' ' ' ~ 60 50 40 30 20 10 0

ppm from hexamethy 1 d i s i 1 oxane

Figure 1 22.5 MHz I 3 C NMR spectra o f poly-1-hexene

a: ethanol-quenched polymer, b: 02-quenched polymer

290 T. Shiono, K. Ywhida and K. !bga

Table 2 Calculated and observed chemical

shifts of structures I and IIa

Chemical shift

(ppm from hexamethyldisiloxane)

calcd' obsd b carbon

(22.5 MHz)

a 11.83 12.26

b 20.87 21.35

C 27.93 26.84

d 32.69 32.67

e 30.89 30.55

f 37.45 38.45

1 18.09 18.07

2 28.43 28.25

3 39.46 40.57

4 36.95 37.21

5 35.03 35.19

35.35

6 25.38 24.00

24.58

7 9.33 8.59

8.90

8 34.88 35.71

9 32.1 9 31.05

31.70

1 ' 66.09 64.16

2' 38.42 36.12

3' 34.64 34.52

8' 29.88 29.46

a See Figure 1

The resonance peaks of chain end carbons are

split due to the diastereomeric structures.

Calculated according to the Lindeman-Adams Rules

23. Synthesis of the Tenninal& Hydmyhted Po&olefim 291

attributed hydroxyl end groups(C1 I , C ~ I , C ~ I and c81) are about

70% of those attributed to ethyl end groups(C4-C7) (see Figure

1 b) , indicating that approximately 70% of Zn-carbon bonds could be transferred to a hydroxyl group.

Propene Polymerization: Propene polymerization was

performed using the TiC13/A1(C2H5)2C1 catalyst system in the

absence and presence of Zn(C2H5)2. The results obtained are

summarized in Table 3. Addition of Zn(C2H5I2 caused a marked

increase in the ethanol soluble fraction, which may be attributed

to decrease in molecular weight. In fact, the molecular weight

of ethanol insoluble polymer was found to decrease from 2.7 x 1 O 5

to 3.3 x l o 3 by adding Zn(C2H5)2. The number of polymer chains,

on the other hand, increased from 0.014 to 0.76 mol/mol-Ti, which

indicates that approximately 98% ((0.76-0.01 4)/0.76 x 100) of the polymers were formed with the chain transfer by Zn(C2H5)2.

Contrary to 1 -hexene polymerization, addition of Zn(C2H5)2 did

not affect polymer yield under these conditions.

The results of 02-quenched polymers are also shown in Table

3. Quenching by oxygen changed neither polymer yield nor

molecular weight.

Structure of Ethanol-soluble Polypropylene: Figure 2 shows

the 3C NMR spectra of ethanol-soluble polymers, which display

several weak peaks besides three major 3C resonances attributed

to Saa, TBB and PBB in head-to-tail sequences of propene units.

Those resonances of ethanol-soluble polymers can be assigned as

indicated in Figure 2a and Figure 2b (For more details see Table 4).4,5) The resonances of the chain end carbons are split into

doublets due to the difference in the diastereomeric structures

of the neighboring two methyl groups. The intensities of the

weak peaks attributed to the isopropyl end group (C1 and C2) and

secondary butyl end group (C4-C7) are almost equal (see Figure

2a), which implies that the living polymer chains were

predominantly transferred by Z ~ ( C Z H ~ ) ~ . On the other hand, the

intensities of the peaks attributed to hydroxyl end groups (C1l,

C21, C31 and C9) are about 70% of those attributed to secondary

butyl end groups (C4-C7) , indicating that approximately 70% of Zn-carbon bonds could be transferred to a hydroxyl group.

?:

P

Run no. TiC13 A1(C2H5)2C1 Yield [g/mmol-Ti] Quencher Mn Polym. Chain X [mmol J [mmol/dm3] [mmol/dm31 Ethanol Insol. Ethanol Sol. [x103J [mol/mol-Ti] f

4

B Table 3 Results of propene polymerization with the TiC13/A1(C2H5)2Cl/Zn(C2H5)2 catalyst system e,

a

T450 0.34 20 0 3.9 0.03 ethanol 270 0.014

T466 0.31 20 0 5.9 0.06 ethanol - _ "448 0.30 20 240 2.5 0.73 ethanol 3.3 0.76

T459 0.33 20 240 3.2 1.1 ethanol - - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ - - - T464 0.39 20 240 2.5 0.72 oxygen 3.1 0.80

T467 0.36 20 240 2.9 1 .o oxygen - - ~ ~

Polymerization conditions; heptane = 0.025 dm3, propene = 3 dm3(S.T.P.), 0.05 dm3 stainless

steel autoclave, 4OoC, 1 hr.

23. Synthesis of the TenninaUy Hydroxkated Fvljvlefiins 293

1 '66 F 7 $ ' c C-C-C-CfC-C+,C-C-C~C

1 2 3 &TBi '4 5 6 7

Pse 9

c c c c 1 1 1 I

HO-C-C-C-CfC-Cf,C-C-C-C

1-T3 SmTee4 5 6 7

b

I " " I " " I " " I " " ~ " " ~ " " ~ " " ~

50 40 30 20 10 0 70 60

ppm from hexamethyldisi loxane

Figure 2 22.5 MHz 13C NMR spectra o f the ethanol-soluble polypropylene

a: ethanol -quenched polymer, b: 02-quenched polymer

294 T. Shiono, K. Yoshida and K. Soga

Table 4 Calculated and observed chemical shifts of structures

I11 and IVa

chemical shift (ppm from hexamethyldisiloxane)

carbonb calcdC obsdd obsde Zambe 11 i Hayas hi

(22.5 MHz) (67.5 MHz) et al. et al.

1 20.59 20.07 20.51 20.67 20.55

21.91 21.74 21.76 21.79

2 23.89 23.24 23.70 23.98 23.80

23.32 - - 23.88

3 42.49 - - - - 4 41.83 42.05 42.91 - -

42.72 43.38 - - 5 30.49 29.68 30.26 - -

29.90 30.30 - - 6 27.82 26.81 27.49 27.92 27.98

28.79 28.69 28.77 - 7 8.84 9.20 9.09 9.13 9.03

9.59 9.30 9.27 -

1 ' 68.59 66.24 66.30 - - 2' 33.69 31 .13 31.80 - - 3' 39.52 39.05 39.87 - - 9 15.62 14.16 14.49 - -

16.98 15.79 - -

a See Figure 1

The resonance peaks of chain end carbons are split due to

the diastereomeric structures.

Calclated according to the Lindeman-Adams Rules

ethanol soluble polymers, CDC13, room temperature

ethanol insoluble polymers, CD2C14, 120°C

23. Synthesis of the Terminally Hydmyhted Polplefins 295

Judging from the resonances in the methyl regions, these

polymers are not isotactic but atactic. However, the peaks at

36.7 ppm (Toly), 29.2 ppm ( T B ~ ) and 29.9-29.0 ppm (S,B) assignable

to the carbons in the sequences with inverted propene cannot be

observed. From these results, the following scheme may be

applied to the present polymerization.

C I

C I

n C=C C Zn (C2H5 ) 2 I

Ti-C-C - Ti-(C-C),-C-C > C2H5Zn-(C-C),-C-C

'2 1 'ZH50H C I

HO-(C-C),-C-C

The number average polymerization degree was estimated from

the intensities of chain end and main chain carbons in 13C NMR

spectra to obtain approximately 10 and 8 for polypropylene and

02-quenched polymer, respectively.

Structure of Ethanol-insoluble Polypropylene: Figure 3a

shows the expanded 3C NMR spectrum of ethanol-insoluble polymer

obtained in the absence of oxygen. Each resonance peak can be

assigned as indicated in the figure. The number average

molecular weight estimated from the spectrum was approximately 4

x lo3, which is in good agreement with that measured by GPC (3.3

x lo3). The spectrum of polypropylene obtained in the absence of

Zn(C2H5)2 was also measured for reference. In the spectrum,

however, no resonance except those assigned to main chain carbons

could observed due to the very high molecular weight (2.7 x 10 1. 3C NMR spectrum of ethanol-insoluble

02-quenched polymer. Each resonance peak can be assigned as

indicated in the figure by assuming the polymer structure to be

(IV). However, there is some mismatching in the peak

intensities, i.e., intensities of the C,I, C2t, C31 and Cg

5

Figure 3b shows the

296 T. Shiono. K. Yoshida and K. Soga

1 '66

F ' F F F c-C-C-CfC-Cf"c-C-C-C

1 2 3 S,Ts64 5 6 7

'66 9

F F F F c-c-c-cfc-ct"c-c-c-c 1-73- S,Ts64 5 6 7

".

'6

-; ~ l " " l " " l " " l " " l ' ' ' ' I 7 0 6 0 50 4 0 3 0 2 0 10 0

p p m f r o m h e x a m e t h y l d i s i l o x a n e

Figure 3 67.5 MHz 13C NMR spectra o f t h e ethanol- insoluble polypropylene

a : ethanol -quenched polymer, b: 02-quenched polymer

w

IY

23. Synthesis of the Terminally Hvdmxyhted Polvolefins 297

a

24 23 22 21 20 19

ppm from hexamethyl d i s i loxane

Figure 4 67.5 MHz ’3C NMR spectra i n the methyl region f o r ethanol-

insoluble polypropylene.

ethanol-quenched, c: w i th Zn(C2H5)2. 02-quenched

a: without Zn(C2H5I2, b: w i t h Zn(C2H5I2,

298 T. Shiono, K. Yoshida and K. %ga

5. 0 -0 E W

I I b

C

I I I 1

50 100 1 5 0 200

Temperature [ O C J

Figure 5 DSC curves (second run) of ethanol - insoluble polypropylene

a: without Zn(C2H5I2, b: w i t h Zn(C2H;I2, ethanol-quenched,

c: w i t h Zn(C2H5)2, 02-quenched

23. Smthe-sis of the Tenninully Hydroxyrlated Polyolefins 299

carbons in the hydroxyl end group, are much weaker (ca. 1/31

compared with those of (C4-C7) carbons in the secondary butyl end

group. Such a tendency was also observed in the ethanol-soluble

polymers (for more details see Figure 3). Taking into considera-

tion the fact that the peaks attributed the C1 and C2 carbons in

structure (111) disappeared completely in Figure 3b1 there may

exist some other terminal groups which display very broad

resonance peaks.

The expanded 13C NMR spectra in the methyl region of

ethanol-insoluble polymers are shown in Figure 4, indicating that

addition of Zn(C2H5I2 caused a slight decrease in catalyst

isospecificity. It may be said, however, that the TiC13/

A1(C2H5)2Cl/Zn(C2H5)2 catalyst system is highly isospecific and

that addition of oxygen barely affects the microtacticity of

polypropylene.

The DSC curves of these polymers are illustrated in Figure

5. The polymer obtained in the absence of Zn(C2H5I2 shows the

melting point at around 163'C (Figure 5a), while that of those

obtained in the presence of is around 150'C with a

shoulder at approximately 158°C. The heat of fusion was

estimated to be about 100 and 60 J/g for the former and latter

polymers, respectively. Such differences may be caused not only

by the difference in molecular weight but also by the difference

in isotacticity.

In conclusion, the present method appears to be very useful

for the syntheses of functionalized isotactic polyolefins.

References

1. Y. Doi, G. Hizal, K. Soga, Makromol.Chem. 188, 1273 (1987) 2. A. K. Ingberman, I. J. Levine, R. J. Turbett, J.Polym.Sci.,

Part All Q, 2781 (1966)

3. J. J. Boor, J.Polym.Sci.,Part C 1, 237 (1963) 4. A. Zambelli, P. Locatelli, G. Bajo, Macromolecules 12, 154 (1 979)

5. T. Hayashi, Y. Inoue, R. Chujo, Macromolecules 21, 2675 (1988)


301

24. Conversion of Titanacyclobutane Complexes for Ring Open- ing Metathesis Polymerization into Ziegler-Natta Catalysts

Incoronata Tritto., Robert H. Grubbsb

.Istituto di Chimica delle Macromolecole del CNR,

bArnold and Mabel Beckman Laboratories of Chemical Synthesis,'

Via E. Bassini 15, 20133 Milano (Italy)

California Institute of Technology, Pasadena CA 91125 (U.S.A.)

ABSTRACT

Titanacyclobutanes, catalysts for living ring opening

metathesis polymerization (ROMP) of strained cyclic olefins, have

been transformed into Ziegler-Natta catalysts. The synthetic

routes that allow the transformation of 3,3-dimethylcyclopropene-

titanacyclobutane 1, the most effective initiator of these ROMP

polymerizations, and of trisubstituted titanacycles, such a6 3 ,

into the corresponding chlorine or ethoxy derivatives are

reported. When trimethylaluminum is added to 1 ,8 and 9 new

alkylidene methyl-bridged bimetallic complexes, that can be

considered as borderlines between metathesis and Ziegler-Natta

catalysts, are obtained.

INTRODUCTION

Ring-opening olefin metathesis polymerization (ROMP) of

strained cyclic olefins is catalyzed by a variety of metathesis

catalytic systemsl. Recently well-characterized alkylidene

catalysts, which are able to produce living polymers, were

'Contribution no. XXXX

302 I. Tritto and R. H. Grubbs

developed.2 Titanacyclobutanes have been shown to be able to

give the first well-defined living polymerization of norbornene2.

and to catalyze the synthesis of block copolymers and conductive

polymers with novel structures3. The mechanism involves the

opening, at the polymerization temperature ( 6 5 ' C), of the

titanacyclobutane 1 to titanium-carbene complex 2, that, after

[ Z + 2 ] addition of norbornene, forms a new titanacyclobutane 3 .

1 1 2 3 4

Metal-carbenes have also been suggested as intermediates in

Ziegler-Natta polymerization4, although up to now all the

experimental results for titanium based catalysts, are

inconsistent with such a hypothesiss~~. However since Ziegler-

Natta polymerizations are mainly catalyzed by titanium

alkylcomplexes, we attempted to transform the metathesis active

catalyst into a Ziegler-Natta catalyst. These transformations

could have potential uses in obtaining poly-alpha-olefin-

polyalkenamer block copolymers. We wish to report herein the

synthesis of alkyltitanocene chlorides from titanacyclobutanes

and of new methyl-bridged alkylidene complexes we have

discovered in our attempts to perform this transformation.


3,3-dimethylcyclopropene titanacycle 1 is the most effective

initiator of these living ROMP polymerizations, and, like other

titanacyclobutanes, it has been prepared from the Tebbe reagent 5

and the parent olefin in the presence of a Lewis base such as 4-

24. Conversion of TitaMcycrobutane into Ziegkr Tvpe catalyst 303

dimethylarninopyridine (DMAP1.7

5

The metallacycle 1, among

is unique in that it has

alpha-substituted carbene

1

other disubstituted titanacyclobutanes,

been shown to be able to open to the

CpzTi=CH-C(CHs)z-CH=CHz 2. Indeed 2 can

be trapped by several phosphines, and 1 is able to react with

AlMezC1 to afford the bimetallic alkylidene-bridged complex 6 8 ,

6 1

The Tebbe reagent 5 was first prepared by reacting titanocene

dichloride and trirnethylaluminum. Therefore our first appproach

involved the conversion of a substituted Tebbe reagent to a

titanocene alkylchloride by cleavage of the A1-C sigma bonds with

a proton source. The reaction of 5 , the unsubstituted Tebbe

reagent, with 1 eq. of soft protic sources such as EtOH,

isopropanol or piperidine at -40’ C results in the quantitative

formation of CpzTiCH3Cl.

A 1 M e2OE t e

- 4 0 c 5

However the reaction of 6 with EtOH, gives the desired

alkyltitanocenechloride in only a 30% yield and a 70% yield of


3,3,dimethyl-l-butene.

so x

The low yield results from the HC1 produced in the reaction that

cleaves the remaining Ti-C bond. This side reaction can not be

avoided either by using a low temperature such as -100' C or by

using more hindered alcohols.

We tried to circumvent the interfering presence of HC1 by

substituting the p C 1 with p-Me in the complex 6. AlMe3 was added

to the titanacycle 1 and to more complex trisubstituted

titanacycles (Table I) resulting in the formation of new

alkylidene complexes. This new route, consisting in the addition

of 1 eq. of AlMel to Cp2Ti=CHR generated from a

titanacyclobutane, is quantitative by NMR for metallacycles of

modest thermal stability. The structure of 7 has been assigned on

the basis of 'H, I3C NMR data. The bridged CHI group showed

resonances at high field characteristic of the methyl bridged

structure (see Experimental Section); the complete assignment was

made on the basis of 2-dimensional 13C3H NMR.

The trisubstituted titanacycles 8 and 10, derived from the

reaction of 1 with two equivalents of cyclopentene and with one

equivalent of endo-dicyclopentadiene respectively9, can react

with AlMe3 and give the corresponding methyl-bridged complexes.

The yield can not be quantitative as the reaction temperature

24. Conversion of TitaMcycrobutane into Zkgler Tvpe Gatalyst 305

Table I Reaction among Titanacyclobutanes and Awe3

starting Titanacycle

Product ‘H NMR Bimetallic complex d ofpCH3

1

cpzTp 8

4Y

-Q$ 10

9 b

-1.59

-1.7

-1.55d

-1.596

Quantitative NHR yield at -1O’C. b d50% NMR yield after 2 hours at RT. c u308 MIR yield at 65’ C in 15’. d The

is near the temperature at which these bimetallic compounds start

to decompose.

CHI appears as 2 signals since 10 is prepared as a mixture of two isomers’.


The bimetallic complex 7 reacts with 1 equivalent of ethanol

at -40' C, giving the corresponding ethoxide in quantitative

yield (by NMR). The addition of AlEtC12 to 12 at - 4 0 ' C affords

the titanocene alkylchloride.

7 12 13

In order to have a better understanding of the chemistry of

these new bimetallic compounds, we explored their reactivity.

Titanacyclobutanes are known to be able to react with organic

carbonyl groups to give the corresponding methylene derivatives

in excellent yield 1 0 . We tested the Wittig type reactivity of

the complex 7 towards ketones. The reaction of 7 with acetone

(RT, lh 30') gives the 3,3,3-trimethyl-1,4-hexadiene in good

yield.

d

The sterically more demanding benzophenone is reduced to yield

diphenyl methanol after hydrolysis.

If the synthesis of 7 is conducted in CDzClz 30% of the

substituted Tebbe reagent is observed as well.

24. Conversion of TitaMcyrrobutane into Zkgler Tvpe Catalyst 307

A 1 Me3 CPJQ)/ c w 3 2 -

This fact indicates that

must be important.

30%

the partially polarized structure

14 This polarization would allow an electrophilic attack

1 4

on

dichloromethane, indeed AlMe3 alone does not react with CDzC12.

The methyl complex 7 is formed at -40 ' C by reacting 1 with

AlMes/HzO (MAO) and this complex in the presence of an excess of

MA0 polymerizes ethylene.

AIHe&&l C p 2 T k : - p o l ye t h y l e n e

AlMedw d -.'a, -40 c CHZlCY

Moreover complex 7 alone, in absence of any cocatalyst such as

MAO, is able to polymerize ethylene, when dichloromethane is

used as solvent. All these facts are consistent with the recent

evidences for the ion-pair nature of the active species in

soluble Ziegler-Natta polymerizations11. It is very interesting

to observe that this complex can be considered as a borderline

catalytic complex between metathesis and Ziegler-Natta catalysts,

having the possibility to behave as a carbene or as a Ti-C sigma

bond depending on the reaction conditions.

In light of the fact that these bimetallic p-methylbridged

complexes react with non hindered molecules in the same fashion


as the parent metallacycles, we attempted to investigate the

reactivity of 1 and 3 with alcohols.

Treatment of titanacyclobutanes with proton sources such as

HX results in various reactions ranging from clean cleavage of

one M-C bond to metallacycle decomposition. The reaction of

metallacycles below their decomposition temperature with

anhydrous HC1 gives mainly CpzTiCln and the corresponding

alkane. Whatever the decomposition pathway, the direct formation

of a titanocene alkylchloride by reacting H C 1 with almost all di

or tri substituted titanacyclobutanes seems to be precluded.

However softer protic acids like alcohols have been shown to be

able to protonate titanium-carbon bonds of some disubstituted

titanacyclobutanes under mild conditions, obtaining the

corresponding alkoxides.12

By reacting EtOH with I and with the trisubstituted

titanacycle 3, obtained after the insertion of one molecule of

norbornene on I, it is possible to obtain the corresponding

ethoxides, which can Polymerize ethylene after the addition of a

chlorine containing cocatalyst, such as AlEtC12, TiCls.

Since the trisubstituted titanacycle 3 is not very different

from a titanacycle carrying the polymer chain, we can conclude

24. Conversion of TitoMcynobutane into Ziegkr Type Catalyst 309

that in principle it should be possible to obtain an AB block

copolymer, or ABA block copolymer if the ROMP polymerization is

catalyzed by a bifunctional initiat~r'~, by combining olefin-

metathesis polymerization and Ziegler-Natta polymerization. The

major problem will be the non living nature of the latter

polymerizations. We are currently studying both the extension of

these sequences of reactions to chain propagating

titanacyclobutanes, and the conditions that minimize chain-

transfer in Ziegler-Natta polymerizations.

EXPERIMENTAL SECTION

All manipulations of air- and/or moisture sensitive

compounds were carried out using standard high vacuum or Schlenk

techniques. Argon was purified by passage through columns of BASF

RS-11 (Chemalog) and Linde 4A molecular sieves. All sample

weighting of air and/or moisture sensitive compounds was

performed in a vacuum atmosphere dry box equipped with a -40' C

freezer. Toluene and do-toluene were dried and vacuum transferred

from sodium benzophenone ketyl into vessels equipped with teflon

valve closures. dz-dichloromethane was dried over CaH2. The Tebbe

reagents 5, 6 and the titanacyclobutanes 1, 3, 10 and 12 were

synthesized as previously described60'.902.. All the new

reactions, besides the polymerizations, were performed in NMR

tubes. IH and J3C NMR were recorded on a JEOL GX-400 (400 MHz JH,

100 MHz 13C). Chemical shifts are referenced to residual protons

of the deuterated solvents.

General Procedures fnr mtm macti0LI.E . Reagents (if

solids) were weighed and added to an NMR tube in the dry box and


the tube capped with a rubber septum. The tube was brought out

and cooled below the reaction temperature in a dry ice-acetone

bath. The deuterated solvent was added slowly from a gas-tight

syringe so that it cooled before mixing with the solid present.

Any liquid reagent was added on top of the solution by syringe.

The tube was shaken vigorously, put in the precooled NMR probe

and the spectrum recorded.

Selected spectroscopic data are:

7: 1H NMR (400 MHz, C7Da): d 10.03 ( 6 , 1 H, TiCHAl), 6.75-6.68

(m, 1 H CYCHz), 5.50 ( s , 5 H, Cp), 5.35 ( s , 5 H, Cp), 5.04-5.10

(m, 2 H, CHCHz), 1.23 (s, 3 H, C(CB~)Z), 0.96 ( s , 3 H, c(cH3)Z),

-0.24 ( 6 , 3 H, Al(C83)2), -0.31 ( 6 , 3 H, A1(C13)2), -1.6 (6, 3 H,

TiC&Al) . I3C NMR (100 MHz, C7De) C!I 239.45 (d, TiCHAl), 150.99 (d, CHCHz),

111.04 (d, Cp), 108.53 (d, Cp), 108.77 (d, CHCHz, 58,93

(quaternary, CHz€Mez), 33.70 (q, Me), 31,18 (q, Me), -3.57 (q,

TiMeAl), -7.98 (q, AlMez).

The complete assignment was made on the basis of 2-dimensional

'H-"C NMR.

12: lH NMR (400 MHz, C7De) 66.04 ( m , 1 H, CHCHz) 5.681g6, 10 H,

CP), 5.08 ( m , 2 H, CHCHz), ,3.95 (q, 2 H, TiOCHz), 1.64 ( 8 , 2 H,

CBz), 1.17 ( s , 6 H, C(CHa)z), 0.95 (t, 3 H, CHZCKJ)

13C NMR (100 MHz, C7Ds)d153.13 (d, €HCHz), 111.91 (d, Cp), 107.09

(d, CHCHz), 73.79 (d, TiOCHz), 42.93 (quaternary, CHzGMez) 31.67

(9, Me), 19.54 (CH2CHs).

13: lH NMR (400 MHz, C7De) h 5.89 ( 8 , 10 H, Cp), 5.66-5.70 ( m , 1

H, CHCHz), 4.9-5.0 (m, 2 H, CHCH21, 1.97 (s, 2 H, CHz), 0.94 (s,

24. ConversMn of Titanacyrrobutane into Zkgler Tvpe Cutalyst 311

1 3 C NMR (100 MHz, C7Da) 6151.95 (d, CHCHa), 115.44 (dl CP),

109.22 (d, CHCHz), 86.04 (d, TiCHz-), 44,96 (quaternary CHzCMez),

31.63 (9, C(CH3)z.

REFERENCES

1. a) Ivin, K.J. "Olefin Metathesis" Academic Press: London 1983 b) Grubbs, R.H. in "Comprehensive Organometallic Chemistry" Wilkinson, G., Ed. Pergamon Press, Oxford 1982 Vol. 8 pp 499- 551

2 : a) Gilliom, L.R., Grubbs, R.H. J. Am. Chem. SOC. 1986, 108, 733 b) Schrock, R.R., Feldman, J., Cannizzo, L.F., Grubbs, R.H. Macromolecules 1987, 20, 1199 c) Kress, J., Osborn, J.A., Greene, R.M.E., Ivin, K.J., Rooney, J.J. J. Chem. SOC., Chem. Commun. 1985, 875

3. a) Swager, T.M., Grubbs, R.H. J. Am. Chem. SOC., 1987, 109, 895 b) Cannizzo, L.F., Grubbs, R.H., Macromolecules, 1988, 21, 1961 c) Risse, W., Grubbs R.H., Macromolecules, 1989, 22, 1558 d j Risse , W. , Grubbs , R. H. , submitted to Macromolecules

4. Ivin, K.J., Rooney, J. J., Stewart, C.D., Green, M.L.H., Mahtab, R.J. J. Chem. SOC., Chem. Commun., 1978, 604

5. a) Zambelli,A. Locatelli,P.,Sacchi,M.C., Rigamonti,E. Macromolecules, 1980, 13, 798 b) Locatelli, P., Sacchi, M.C., Tritto, I. Zannoni, G., Zambelli, A., Piscitelli, V. Macromolecules, 1985, 18, 627

6 . a) Soto,J., Steigerwald, M.L., Grubbs, R.H. J. Am. Chem. SOC. , 198'2,104 , 4479 b) Clawson,L., Soto,J., Buchwald, S., Steigerwald, M.L., Grubbs, R.H. J. Am. Chem. SOC., 1985, 107, 3377

7. Gilliom, L.R., Grubbs, R.H. Organometallics 1986, 5, 721

8. Tebbe, F.N., Parshall, G.W., Reddy, G.S. J. Am. Chem. SOC.,

9. Gilliom, L.R., California Institute of Technology, Ph.D.

10. a) Brown-Wensley, K.A., Buchwald, S.L., Cannizzo, L.,

1978, 100, 3611

Dissertation Thesis, 1986

Clawson, . L, Ho, S., Meinhardt, D., Stille, J.R., Straus, D., Grubbs, R.H. Pure Appl. Chem. 1983, 55, 1733 b) Pine, S.H., Zahler, R., Evans, D.A., Grubbs, R.H. J. Am.


Chem. SOC., 1980, 102, 3270

11. a) Eisch, J.J., Piotrowski, A . M . , Brownstein, S.K., Gabe, E . J . , Lee, F.L. J. Am. Chem. S O C . , 1985, 108, 7410 b) Jordan, R.F., Dasher, W.E., Echols, S.F. J. Am. Chem. S O C . , 1986 108, 1718 c)Jordan, R.F., Bajgur, C.S., Scott, B. J. Am. Chem. S O C . , 1986, 108, 7410 d) Ewen, J., data presented at this Symposium

12. Cannizzo, L.F. California Institute of Technology, Ph.D Dissertation Thesis 1987

13. Risse,W., Wheeler, D.R., Cannizzo, L.F., Grubbs, R.H. Macromolecules, 1989, 22, 3205

313

25. Modification of High cis- 1 ,4 Polybutadiene by Neodymiun Catalyst

Iwakazu Hattori, Funio Tsutsuni. Mitsuhiko Sakakibara and Kenya Makino

Elastomers Laboratory. Technical Center, Japan Synthetic Rubber Co., Ltd.,

100 Kawaj iri-Cho. Yokkaichi. Mie. 51 0. Japan

ABSTRACT

High &-l, 4 polybutadiene was modified w i th t i n compound.

The polymerization of 1.3-butadiene was carr ied out i n the presence o f a catalyst

comprised o f (a) neodymium 2-ethylhexanoate. (b) t r i i s o b u t y l aluminium, (c) d i i so -

b u t y l aluminium hydride, (d) ethylaluminiumsesqui ch lo r i de and (el acetylacetone.

The reactive polymer was then modified wi th t r i pheny l t i n chloride. The polybutadiene

prepared as described above showed high @-l ,4 structure content and broad molecular

weight distr ibut ion. The t i n content increased with decrease i n the molecular weight

of the polybutadiene. This means that the t i n content increased with the increase i n

the numbers of molecules. This can be also seen by GPC measurement with R I and UV dual

detectors; that is . the intensi ty o f UV absorbance at the low molecular weight region

was higher than that at the high molecular weight region.

chain terminal end.

From these results, t h i s polymer i s thought t o be modified by t i n compound a t the

INTRODUCTION

Polymerization o f 1.3-butadiene by a l k a l i metal compounds i s l i v ing . This l i v i n g

anion can be used f o r modifying the terminals o f polymers or coupling reactions. ' ) ')

However, the physical properties o f the polymer are poor because the c&-1,4 content

of t h i s polymer i s low, between 10 and 40 X .

The c i s - 1 . 4 content o f polymers obtained by t r a n s i t i o n metal ca ta l ys ts i s very

high; The physical propert ies o f t h i s pa r t i cu la r polymer are improved compared w i th

those o f polymers obtained by a l k a l i metal catalysts. However, fu r ther improvement

of physical propert ies by modif icat ion cannot be expected because t rans fer reactions

frequently occur i n the polymerization reaction by t rans i t i on metal catalysts.

Polybutadiene obtained by r a r e e a r t h meta l compounds has very h i g h c i s - 1 . 4 content, and the polymerization i s quasi- l iv ing. ') Therefore, we invest igated i n

d e t a i l the modif icat ion of polybutadiene by neodymiun catalyst wi th t i n compound.

314 I . Hattori, F. Tsutsurni, M. Sakakibara and K. Makino

Table-1. Polymerization o f 1.3-Butadiene a t ROOM TEMPERATURE

Catalyst System Characterist ics o f Modif icat ion

Polymerization

A lka l i metal L iv ing Polymerization Excel l en t

Ex. R L i - cis-1,4 = 10 - 40 X Ex. R- (CH2CH=CHCH2) . -L i ' )

S n C l 4 1 [R- (CHnCH=CHCHz) "1 4Sn

Transit ion metal Non-1 i v i n g Very D i f f i c u l t

Polymerization

- cis- l ,4 90 -96 X

Ex. N i / R J A l

CO / R 3 A l

T i / R 3 A 1

3 Rare earth metal Quasi- 1 i v i n g Polymerizat i i o n

- cis-1,4 97 X

EX. Nd / R 3 A l (with t i n compound)

EXPERIMENTAL

Reagents: 1,3-butadiene (ED: Japan Synthetic Rubber Co., Ltd. 1, cyclohexane (CHX;

Nippon Mining Co., Ltd. ) and t r i pheny l t i n chlor ide (TPTC: Sankyou Yuki Gosei Co., Ltd. )

were used without fur ther pur i f icat ion. Triisobutylaluminun (TIBA), diisobutylaluminun

hydride (DIBAH) and ethylaluminumsesqui ch lo r ide (EASC; Toyo Stauffer Chemical Co., )

were used without fu r ther pur i f i ca t ion . Neodymium 2-ethylhexanoate was prepared from

sodium 2-ethylhexanoate and neodymium t r i c h l o r i d e according t o the usual procedure.

Neodymium 2-ethylhexanoate (1 00 mmol) and acetylacetone (200 mnol) were dissolved

together i n cyclohexane (400 mnol) (NdAC).

Polymerization and Modification: Cyclohexane (60 g) and 1,3-butadiene (6 g) were

placed i n a pressure b o t t l e having an i n t e r n a l volume o f 100 m l under n i t rogen

atmosphere. Separately. a ca ta l ys t was prev ious ly prepared by mixing neodymium 2- ethylhexanoate-acetylacetone complex (0.11 1 mmol), tr i isobutylaluminum (3.11 m o l ) ,

diisobutylaluminum hydri.de (1.55 m o l l and ethylaluminumsesqui ch lo r ide (0.222 mnol)

i n the presence o f 1.3-butadiene (0. 555 mmol). and aging the mixture a t 309= f o r 30

25. Modifiurtion of High d-1, 4-Polybufadiene by Nd Catalyst 315

min. This catalyst was transferred i n t o the pressure bott le.

t o 6 0 C and the r e a c t i o n was c a r r i e d out f o r 1 h a t 60 “C. The po lymer iza t ion

conversion of 1.3-butadiene was nearly 100%. The high Cis-l.4 polybutadiene obtained

was reacted w i th t r i pheny l t i n chlor ide fo r 3 h a t 60°C. The modified polybutadine was

pu r i f i ed by reprecipi tat ion using methanol/toluene.

The mixture was warmed

Analysis: The t i n content i n the polybutadiene was measured by atomic absorption

analysis. The number average-

molecular weight was determined by GPC measurement based on polybutadiene. The

mic ros t ruc ture o f polybutadiene was measured by an I R absorpt ion spectrum method

(Morero method).

The molecular weight was measured by GPC analysis.


Figure 1 shows the t i n content and molecular weight before mod i f i ca t i on as a

function o f TPTC.

L

I 1 I

0 20 4 0 6 0 8 0 100

TPTC/NdAC in molar ratio

Figure 1.

Polymerization condit ion; BD/[NdAC/ DIBAH/ T I B A / EASC/ TPTC/ ED]

= 1000/ [1/ 12/ 28/ 2 / x/ 51 i n molar r a t i o

Tin content and molecular weight as a funct ion o f TPTC

The t i n content increased with the amount o f TPTC added. When TPTC/NdAC molar

When the r a t i o was r a t i o was f i ve , the conversion o f t i n compound was around 24%. between 50 and 70. the conversion o f t i n compound was around 8%.

However, the number of molecules per gram of polymer was 25 XlO-’ mole. The t i n

316 I. Hattori. F. Tsutsumi, M. Sakakibara and K. Makino

content was about 25X10- ' atoms per gram o f polymer. The both values were almost the

same. The polymer obtained by modification with a small amount of TPTC was free from

gel. However, with large amounts of TPTC. some gel was produced.

TPTC/NdAC molar r a t i o (TPTC/NdAC< 20).

Figure 2 shows the t i n content and molecular weight as a function o f NdAC. The

molecular weight increased with amount of NdAC. when the amounts of the other reagents

were constant. Tin content i n polybutadiene increased wi th decrease i n molecular

weight. I n general, molecular weight decreases with increase of active s i te. However,

these phenomena i n the case of the Nd catalyst polymerization described above can be

explained by a lower i n i t i a t i o n efficiency. as shown i n Figure 2. at a molar r a t i o of

Al/Nd below 20.

Next, we investigated i n d e t a i l the modification o f the polybutadiene i n small

NdAC/BD i n molar r a t i o

Figure 2. Polvmerizat ion condition; ED/ [NdAC/ DIEAH/ TIBA/ EASC/ TPTC/ ED]

= 1000/ [x/ 12/ 28/ 2 / 5/ 51 i n molar ra t i o

Tin content and molecular weight as a function o f NdAC

The relat ionship between t i n content and molecular weight as a function of T I B A

i s shown i n Figure 3. The molecular weight decreased wi th increase i n the amount of

T I B A . The t i n content i n the polybutadiene increased w i t h decrease i n molecular

weight. and reached a constant value.

25. Mod$imticn of High cis-1. 4-Polybutadiene by Nd Catalyst 317

I I 1 I

20 40 60 80 100

T I W W C in molar ratio

Figure 3.

Polymerization condition; ED/ [NdAC/ D I B A H I T IBA/ EASC/ TPTC/ BD] 1000/ [1/ 12/ x/ 2 / 5/ 51 i n molar r a t i o

Tin content and molecular weight as a function of T I B A

a

0 C

.rl

r 5

I I I I c 3

‘‘4 (B

- 10 3 2

‘. *.

0 X

-4.-

I I I I

0 5 1 0 1 5 20 25

DIBAH/NdAC in molar ratio

0 5 1 0 1 5 20 2 5

DIBAH/NdAC in molar ratio

Figure 4. Tin content and molecular weight as a function of DIBAH

Polymerization condition; ED/ [NdAC/ DIBAH/ T IHA/ EASC/ TPTC/ BD] = 1000/ [ I / x/ 28/ 2 / 5/ 51 i n molar r a t i o

Table 2. Analytical data of modification of high c&-l,4 polybutadiene with TPTC

Run No. catalyst additional TPTC TPTC Conv. Tin Content GPC Analysis in P o l m r MI Mw h/Mn

atan/g) (lo-') (mnol) ( m n o ~ (mnol) (mnol) (mnol) ( mole Sn/Nd ratio ) NdAC DIBAH TIEA EASC ED

SINE-1 01 SINB- 102 SINB- 103 SINE-104

SINB-107 SINB-101 SINE-1 08

SINB- 1 17 SINE-116 SINE-1 15 SINE-1 19 SINE-120

SINE-1 09 SINE-101 SINE-1 15 SINE-1 10

0.111 1.33 0.111 1.33 0.111 1.33 0.111 1.33

0.222 1.33 0.111 1.33 0.060 1.33

0.111 1.33 0.111 1.33 0.111 1.33 0.111 1.33 0.111 1.33

0.111 0.67 0.111 1.33 0.111 1.33 0.111 2.00

3.11 3. 1 1 3. 1 1 3. 1 1

3.11 3. 1 1 3. 1 1

0.89 1.55 3. 1 1 4.66 4. 66

3. 1 1 3.11 3.11 3.11

0.222 0.555 5 0.222 0.555 20 0.222 0.555 50 0.222 0.555 70

0.222 0.555 5 0.222 0.555 5 0.222 0.555 5

0.222 0.555 5 0.222 0.555 5 0.222 0.555 5 0.222 0.555 5 0.222 0.555 5

0.222 0.555 5 0.222 0.555 5 0.222 0.555 5 0.222 0.555 5

24 12 6. 9 7. 9

20 24 36

24 34 29 40 38

15 24 29 43

21.9 43. 8 64. 0 103

18. 5 21.9 33.7

22.7 31.2 27. 0 37. 1 35. 4

14. 3 21.9 27. 0 39. 6

4. 1 35. 6 8. 7 4. 0 35. 2 8.8 3. 9 35. 1 9. 0 3. 9 34. 7 8. 9

6. 5 37. 1 5. 7 4. 1 35. 6 8.7 3. 7 101.8 27. 5

9. 7 69. 8 7. 2 6.6 60. 7 9. 2 5. 3 86.4 16.3 4.3 48.611.3 5. 0 40. 5 8. 1

6. 2 45.3 7.3 4. 1 35. 6 8. 7 5. 3 86. 4 16. 3 - - - - - - - - -

(u

a P

25. Modifation of High 8-1,rl-Polybutudime by Nd Catalyst 319

Figure 4 shows the t i n content and the molecular weight as a funct ion of DIBAH.

The molecular weight c l e a r l y decreased w i th increase i n the amount of O I B A H added.

The t i n content i n the polybutadiene increased w i th decrease i n the molecular weight.

I t can be seen by extrapolat ing the amount o f D I B A H t o zero that the t i n content was

almost zero at zero concentration o f DIBAH.

The other ana ly t i ca l data are sumnarized i n Table 2. F igure 5 shows t h e i n f r a r e d absorp t ion spectrum o f the non-modif ied po ly -

butadiene. The peak a t 740 cm-' i s based on the cis-1.4 structure o f polybutadiene,

and those at 910 cm-' and at 960 an-' are based on the v i n y l structure and the trans- 1,4 structure, respect ively. From these resul ts, the microstructure o f the poly-

butadiene was determined as fol lows; the cis-1.4 content was 97.4% and the m - l , 4

and v i n y l contents were 1.2% and 1.4%, respectively.

90

70

40

30

Microstructure of p o l ybut adiene

- cis-1.4 = 9 7 . 4 X

- t rans- l ,4 = 1 . 2 X

v i n y l = 1 . 4 X

Figure 5. Infrared absorption spectrum of non-modif ied polybutadiene

Figure 6 shows the GPC chart o f the non-modified polybutadiene. Measurement o f

GPC was car r ied out w i t h R I and UV (254 nm) dual detectors. The molecular weight

d i s t r i b u t i o n (MWD) obtained by R I detector was very broad. However. the MWD by UV

de tec tor cannot be measured because the non-modif ied polybutadiene g ives no U V

response.'

The GPC chart o f the modified polybutadiene i s shown i n Figure 7. The MWD by R I detector was very broad. and the MWD by UV detector was sharp. I n the GPC chart, the

number of polymers increased exponent ia l ly w i t h decrease i n molecular weight.

indicated that the number of polymer terminals at the low molecular weight region was I t

320 I. Hattori. F. Tsutsumi, M. Sakakibara and K. Makmo

I"'"'''''''

Figure 6. GPC chart of the NON-modified polybutadiene

254 m UV ABSORPTION SPECTRUL

High Uolacular Iaight

26 24 22 20 18 16 14

G P C C W N T

Figure 7. GPC chart of the polybutadiene modif ied with TPTC

25. Modifimtion of High ciS-l,I-Polybutadiene by Nd Catalyst 321

much higher than a t the high molecular weight region.

compound i s connected t o the terminal end o f the polymer.

This resul t suggests that t i n

On the other hand, a l l y l i c - t y p e aluminum exh ib i t s f a c i l e rearrangement5' as

The dialkylaluminun of the a l l y l i c - t ype aluninun i s substi tuted with shown i n Eq. ( 1 ) .

carbon dioxide, acyl chlorides and s i l i c o n chlorides. ''

H R ' H R ' \ / A \ /

C=C-C - A l R " 2 ,-. R " 2 A 1 - C-C=C \ H/ R ' H' R '

\

Organic groups attached t o a wide va r ie t y o f metals w i l l r ead i l y exchange with

chlorine atoms bound to t in ' ' as shown i n Eq. (2).

3 C - M t 4Sn-Cl - + C - S n f t MC1 ( 2 ) M; A l . Mg, L i . Na, K or Zn

From these results, we assuned the fol lowing mechanism;

Nd' -CHzCH=CHCHp- (CHpCH=CHCH?) n- + R ' A l R a

R ' ; H or R I Nd'; act ive s i t e

R?Al-CHpCH=CHCHp- (CHzCH=CHCHa) n- t Nd'R'

I R"SSnC1

R"JSn-CHZCH=CHCHz- (CHzCH=CHCH?) "- + Nd'R' + R Z A l C l R "

However, the precise.mechanism of the reaction i s not c lea r l y understood and w i l l

be studied i n the future.

REFERENCES

1. N. Ohshima. F. Tsutsuni and Sakakibara. I R C Kyoto. Oct. (1985) 16A04

2. N. Nagata, T. Kobatake. H. Watanabe. A. Ueda and A. Yoshioka. Rubber Chem. Technol.,

3. H. L.Hsieh and H.C.Yeh. ibid., 58. 117 (1985)

4. J. Xianzhong, P. Shufen, L. Yuliang and 0. Jun. Sientia Sinica (Ser. B), 3, 8 (1986)

5. H. Lehkuhl and D. Reinehr. J. Organometal. Chem., 23. C25 (1970) 6. J. J. Eisch. Adv. Organmetal. Chem., Is. 67 (1977)

7. R. C. Pol ler "The Chemistry o f Organotin Compounds. "Academic Press, N. Y . , 1970, p 1 1

- 60, 837 (1987)


323

26. Homo- and Co-Polymerization of Ethylene with the Highly Active TiC14/THF/MgC12 Catalyst

I.Kim, M.C.Chung, H.K.Choi, J.H.Kim, and S.I.Woo

Department of Chemical Engineering, Korea Advanced Institute of Science and Technology,

P. 0. Box 131, Cheong-Ryang, Seoul, Korea

ABSTRACT

Homo- and co-polymerization of ethylene were performed by

using a catalyst system composed of TiCla/THF/MgCl2 complex with

AlEt, at 70°C. In order to investigate the role of MgC1, in the

catalyst 6 catalysts with different composition (Mg/Ti - 0.42 -16.5) were characterized by means of elemental analysis, IR

spectroscopy, x-ray powder diffraction, and SEM technique. The

catalytic activity of polymerization increased linearly with the

Mg/Ti ratio of catalyst within the experimental range. The activity of copolymerization with 1-hexene also increased with Mg/Ti

ratio. The enhancement of polymerization rate by the addition of 1-hexene in the reaction medium was observed only for the cata-

lyst of Mg/Ti ratio smaller than 2.5. The effect of crystallization conditions during the catalyst preparation on the chemical composition and physical structure of catalysts was discussed.

The variation caused by different crystallization conditions had

considerable influences on the rate profiles of homo-and co-

polymerization of ethylene.

INTRODUCTION

Bimetallic complexes containing magnesium compound, titanium

compound, and electron donors, when combined with aluminum alkyl cocatalyst, show high catalytic activity in ethylene polymeriza-

tion'- ) . Bimetallic halide complexes of Mg and Ti can be pre-

pared by reacting MgC12 with TiCla at a temperature of from 25

-150 "C in electron donor solvents3'. Stoichiometric reaction pf

MgCl,(THF), with Ticla in ethyl acetate is known to yield

C1aTi(p-C1)2Mg(CHICOOC2Hs)4a'.

324 I. Kim, M. C. Chung, H. K. Choi, J. H. Kim and S. I. Woo

Likewise reaction between MgCl,(THF), and TiCl,(THF), in THF

yields three different complexes with defined structure, depend-

ing on the molar ratio of the substrates”-’’. Formation of

discrete chemical complex between Mg compound and Ti compound may

not be necessary for achieving a boost in polymerization acti- vity7’. In this catalyst system MgC1, play an important role in

obtaining a highly active catalyst without regard to the forma-

tion of discrete chemical complexes between MgC1, and TIC1,.

However, there are dearth of published data on the role of MgC1,

associated with the ability to enhance the catalytic activity.

The purpose of the present study was to investigate the role

of Mg compound affecting the activity of TiClo/THF/MgC1, Catalyst

on the homo- and co-polymerization of ethylene. In addition

we prepared Mg/Ti bimetallic catalysts of different chemical com-

position and physical structure by changing the crystallization

conditions. The activity and polymerization rate profiles of

these bimetallic complexes were evaluated in the homo-and copo-

lymerization of ethylene.

EXPERIUENTAL materials. Polymerization grade of ethylene (Yukong Ltd.,

Korea) and nitrogen of extra pure grade were further purified

with the columns of Fisher RIDOX catalyst and molecular sieve

5A/13X. 1-Hexene (Aldrich, USA) was passed through molecular

sieve 5 A and 13 X. n-Hexane of extra pure grade (Duksan, Ltd., Korea) was dried over sodium metal in a nitrogen atmosphere, and

passed through the columns of CaS0, and molecular sieve 5 A

before use. Analytic grade of tetrahydrofuran (J. T. Baker Chem.

Co., USA) was purified by refluxing with LiA1H4 for several

hours. Titanium tetrachloride, triethylaluminum, and anhydrous

magnesium chloride (Aldrich, USA) were used without further puri-

f ication,

Catalysts preparation. In a 2 1 round bottom flask equipped with a stirrer, condenser, and inlet tube for N,, 120 mmole of

MgC1, was mixed with 1 1 of pure THF under nitrogen. The temper-

ature of the reaction mixture was subsequently increased by means

of heating bath to boiling point of THF while vigorous stirring.

After MgC1, was completely dissolved, the homogeneous solvate was

divided into 10 parts with the same volume. Prescribed amounts

of TiC1, were added dropwise for 15 min to each part at room

temperature. Upon complete addition the contents of flask was

26. Okfin Polymerization with TiCl,/THFIMgCl, Cotalyst 325

refluxed for 2 hr while stirring. After MgC1, and TiC1, are

dissolved, the catalyst composition was isolated by precipitation with n-hexane at room temperature. In order to investigate the

effect of precipitation temperature yellow solid complexes were

obtained by changing the precipitation temperature to 60"C, O"C,

and -10°C in addition to room temperature. The supernatent

liquid was decanted then the yellow solid complex was washed with

100 ml of n-hexane three times. These solid complexes were dried

at room temperature in vacuum, and stored under inert atmosphere. Alternatively, homogeneous solution obtained by dissolution

of 12 mmole of anhydrous MgC1, in 100 ml of THF was precipitated

at room temperature by adding 300 ml of dry n-hexane. This white

solid MgC1, THF complex was washed and dried. TiC1, THF complex

was prepared by the similar method; dissolving TiC1, in THF,

separating the yellow complex by n-hexane, washing, and drying. Polymerization. Slurry polymerization was performed in a 1 1

autoclave under a constant pressure of ethylene. A prescribed amount of AlEt, and 500 ml of n-hexane were introduced into the

reactor in a nitrogen stream. 1-Hexene was also introduced in

the case of copolymerization. After evacuation, ethylene was

introduced at the polymerization temperature. Polymerization was

started by breaking the glass ampoule containing the prescribed

amount of catalyst. The rate of polymerization was determined

from the rate of ethylene consumption, measured by a hot-wire

flowmeter with a personal computer directly connected to it

through A/D converter. Details of polymerization procedures were described elsewhere').

Analyses The content of titanium was determined photometri-

cally (Beckman model 35) according to the method employing H201

and H,SO,. Mg was evaluated through atomic absorption spectro-

scopy (Allied Analytical Systems). Chlorine was determined by

back titration according to Volhard's method*). The amount of

THF was measured by hydrolysis-GC methodse). FTIR spectra were recorded with a instrument with 25 mm NaCl window using a mull

technique containing each sample. X-ray analysis was carried out

in a special cell with a poly(ethy1ene terephtalate) film window

on a Rigaku Geigerflex 2013 diffractometer with monochromatic

copper radiation. The morphology of catalysts was examined using

scanning electron microscope (SEM) technique at inert atmosphere.

Average particle size and particle size distribution of polymer

and catalvst were determined bv MALVERN 2600C microDhotosizer


instrument.

RESULTS

Elemental Analysis. The dissolution of TiCl, and MgC1, in

THF according to Mg/Ti ratio yielded yellow homogeneous solvates.

Bimetallic complexes were obtained by precipitation with excess

of n-hexane. It was analyzed at this point f o r Mg and Ti content since some of the Mg and/or Ti compound might have been lost dur-

ing precipitation of solvate complex. The results of elemental

analysis of the bimetallic complexes of different Mg/Ti ratio are

given in Table 1 as well as MgC1,THF and TiC1,THF complex. The

experimental formulas shown in Table 1 are calculated based on

the results of elemental analysis.

Table 2 shows the results of element analysis of bimetallic com-

plex catalysts cocrystallized at different temperatures. The

mole ratio of Mq to Ti in the precursor solution is 3 regardless

of crystallizaton temperature. However, the final compositions

of Mg and Ti were deviated significantly from this ratio. This is

due to the differences in the solubility of MgC12 THF and TiC1, THF complexes to THF and n-hexane at different crystallization

temperatures. At the higher crystallization temperature, the

solubility of TiC1, THF complex was smaller than that of MgC1,

THF complex and vice versa. Accordingly Mg/Ti ratio in

Table 1. Chemical compositions of MgC12 THF, TiC1, THF, and

various TiC1./THF/MgC12 complexes.

Mg Ti C1 THF Mg/Ti Formular obsd. Complex mmol mmol mmol mmol Ti,Mg,Cl,(THF),

9 g 9 4 ----

cald. obsd. x Y z n

COMPol 0.00 2.64 10.82 5.81 1.0 0.0 4.1 2.2 COMP02 4.91 0.00 11-80 9.82 0.0 1.0 2.4 2.0

KIOl 0.73 1.75 9.27 8.03 0.25 0.4 1.0 0.4 5.3 4.6

KI02 1.45 1.50 8.71 8.09 0.50 1.0 1.0 1.0 5.8 5.4 K103 1.79 0.85 10.14 7.72 1.00 2.1 1.0 2.1 11.9 9.1 K104 2.25 0.87 8.67 8.27 1.50 2.6 1.0 2.6 10.0 9.5

K105 3.51 0.67 9.80 7.42 3.00 5.2 1.0 5.2 14.1 11.0 K106 5.76 0.35 8.42 7.55 10.00 16.5 1.0 16.5 24.1 21.6

26. Okfin Polymerization with TiCl,lTHFIM&12 Catalyst 327

Table 2. Chemical compositions of various complexes crystallized

at different temperatures. Calculated Mg/Ti ratio is 3.

Mg Ti c1 THF Cryst. temp. Mg/Ti

Complex wt% wt% wt% wt% ("C)

K107 10.00 1.67 32.62 55.71 60 11.87

KI08 8.53 3.20 34.74 53.52 25 5.27

KI09 7.67 3.60 35.00 53.73 0 4.19

KIlO 5.80 3.73 33.15 57.32 - 10 3.06

KI1la 14.30 9.19 76.50 trace 25 5.27

a: KI05 was prepared by washing KI08 with excess AlEt,.

the bimetallic complex becomes smaller as the crystallization temperature decreases.

Infrared Spectroscopy. The infrared spectra of neat THF,

MgC12.r(THF)z.o, and TiC1a.I(THF),., complex are shown in Fig. 1. The infrared spectrum of neat THF is characterized by an asymme-

trical C - 0 - C stretching band at 1071 cm-l and a symmetrical band

at 913 cm-l. The most important changes in the i r spectrum of THF as a result of complexation with MgC12 occurs in the bands asso-

ciated with the C - 0 - C vibrations. The asymmetrical and symmetri-

cal c - 0 - C stretching bands shift to lower frequencies at 1038

cm-I and at 890 cm-l, respectively. In addition, new band is appeared at 919 cm-I in MgCl,-.(THF)a.o complex due to the

symmetry change arising from the complex atom. These bands are

splitted and shifted to lower wavenumbers 994, 950, 920 and 828

cm-I in TiC1,-l(THF),-, complex. The larger red-shift of C - 0 - C

stretching bands of THF after complexation reaction with TiC1,

can be explained by the more electron transfer from oxygen to

TiC1, than MgCl,, which agrees with the fact that TiC1, is more

Lewis acidic than MgCl,.

The magnitude of shift in the C - 0 - C bands was changed with

Mg/Ti ratios as shown in Fig. 2 and Table 3. The asymmetrical

C - 0 - C band is shifted to 1023 cm-l when Mg/Ti ratio of the com-

plex is 0.42 (KIO1 catalyst in Table l), and to 1035 cm-l at

Mg/Ti 116.46 (KI06 catalyst). The symmetrical C - 0 - C band is also

shifted to 828 cm-l for KIOl catalyst and to 887 cm-l for K106

catalyst. The higher the ratio of Mg/Ti is, the smaller the

red-shift in the C - 0 - C stretchina band of THF. At MQ/Ti = 16.46,

328 I. Kim, M. C. Chung. H. K. Choi. J. H. Kim and S. I. Woo

t I l l I I l l I I * I l l , I I I I

1600 1200 800

WAVENUMBER, CM- I

Figure 1. FTIR spectra of ( a ) neat THF, ( b ) MgCl,.,(THF),.,, and

( C ) TiC14.1(THF)2.0 Complex.

the pattern of infrared spectrum of K106 is very similar to that

of MgC1,~,(THF),.,. A new band not present in the ir spectrum of

neat THF appears for all complexes between 919 c m - I and 922 c m - I ,

which is not sensitive to Mg/Ti ratio. Another characteristic

band is observed between 951 cm- and 958 c m - 1 f o r the catalysts

of Mg/Ti ratios less than 2.59, which is also insensitive to

Mg/Ti ratios. These different kinds of i r bands must be due to

the different mode of complexation THF in the Mg-Ti bimetallic

comDlexes.

26. Olefin Polymerization with TiC141THFIMgC12 Cahlyst 329

X-ray Diffraction Study. The powder x-ray diffraction patterns of MgCl,.,(THF),., and six catalysts are shown in Fig.

3. MgC12.a(THF)2.0 complex has an XRD pattern, completely different from that of anhydrous MgC1,. For MgCl,.,(THF),., complex, the strong 28 reflection appears at 20.0°, 22.1", and 31.9". The diffraction pattern of the catalyst of high Mg/Ti ratio, i.e., K106 catalyst, are similar to that of

MgC12.,(THF),.,, which is true also in the case of infrared spectrum. However, new crystalline complexes are obtained as the Mg/Ti ratio of catalyst decreases. The strong reflections are observed at 12.6" and 17.9" for KIOl catalyst, and 11.0", 17.9",

and 33.7" f o r K102 catalvst. All the catalysts and

1600 1200 aoo WAVENUME ER, CM-l

Figure 2. FTIR spectra of various TiCl,/THF/MgCl, complexes; (a) K106 in Table 1, (b) KI05, (c) KI04, (d) KI03, (e) KI02, and (f) KIOl.

330 I. Kim, M. C . Chug, H. K. Choi, J. H. Kim and S. I. Woo

Table 3. Infrared bands of THF, MgCl,THF, TiC1,THF and M g - T i

bimetallic complexes.

diagnostic IR bands

Compositions ( c m - l )

1 0 2 0 3 0 4 0 5 0 8 0

2 8

Figure 3. x-ray diffraction patterns of (a) M g C 1 2 . 4 ( ~ ~ ~ ) z . , ,

( b ) K106 ( c ) KI05, Id) KI04. fe) KI03. f f ) KI02. and 1 4 ) KIO1.

26. Olefin Polymwizatian with TiC141THFIMgC12 Catalyst 331

MgC12.a(THF)2.0 complex show very weak diffraction patterns

compared with anhydrous MgC1,. This might be due to the low

crystallinity or the small size of crystallites in the Mg-Ti

bimetallic complexes.

Morphology of Mg-Ti Bimetallic Complexes. MgC1JTHF/TiC14

complexes show a different morphology with Mg/Ti ratios. Details

of inner morphology of catalyst particles were studied with high

magnification (x 6,000 or x 12,000) SEM. The catalysts of low

Mg/Ti ratio (KIO1 and KI02) are composed of the agglomers of

subparticles having flakes-shape (Fig. 4). The size of the flakes ranges between 1.0 -5.0 p . These flakes type particles are very

dense and are probably formed in the early stage of

coprecipitation due to various habit modifications brought about

either by Mg and Ti ions or molecules present in solvate. The

catalysts of high Mg/Ti ratio (KI05 and K106) are also composed

of the agglomers of subparticles (Fig. 5). The size of

subparticles ranges between 0.2 -0.5 p , which is about ten times

smaller than that of KIOl or KI02 catalyst. These catalysts are

less dense and the more porous than KIOl and K102 because of the

free void space among the agglomers.

Ethylene Homo- and Co- polymerization. Ethylene homopolymer-

ization and copolymerization with 1-hexene as a comonomer were carried out at 70 "C using AIEtl as a cocatalyst. The rate profiles of homo- and co-polymerization were changed drastically

as the Mg/Ti ratio of the catalyst was changed. In homopolymer-

ization the time to reach maximum rates become6 short as Mg/Ti

ratio of the catalyst increases (Fig. 6). At the low Mg/Ti ratios

to less than 2.6 the polymerization rate increases slowly to

reach a steady-state value, which remains unchanged f o r an experimental period. At high Mg/Ti ratios, ca., Mg/Ti = 16.5, poly-

merization rate reaches maximum in 3 min. Afterwards, the poly-

merization rate starts to decrease rapidly.

In case of copolymerization of ethylene with 1-hexene, all

catalysts showed decay type kinetic curves within an hour as

shown in Fig. 7. The time to reach maximum activity becomes

short at higher Mg/Ti ratio, as in the case of homopolymeriza-

tion.

The average homopolymerization activity was linearly

increased according to Mg/Ti ratios over an experimental range

(0.42 to 16.46), while the average copolymerization activity

332 I. Kim, M. C. Chung. H. K. Choi, J. H. Kim and S. I . WOO

( b ) Figure 4. Scanning electron microphotographs of (a) KIOl and

( b ) KI02.

26. Okfin Polymerization with TiC141THFIMgC12 Catalyst 333

( b ) Fiqure 5. SEM DhOtOUKaDhS of ( a ) K105 and ( b ) KI06.


1600

\ W

0 20 4 0 6 0

Time, min

Figure 6. The rate profiles of ethylene polymerization catalyzed over ( a ) K106 catalyst in Table 1, ( b ) KI05, ( c ) KI04, ( d ) KI03,

( e ) KI02, and ( f ) KIO1. Polymerization condition: 70"C, 3 atm, AlEtJTiC1, = 128.

1200 I 4 800

3

.- I- m

n. m

=a 400

x

0 0 20 4 0 60

Time, min

Figure 7. The rate profiles of copolymerization of ethylene with

1-hexene. Polymerization conditions and captions are the same as

those in Fig. 6 except for the concentration of 1-hexene = 0.24

mole/l in the reaction medium.

26. Okfin Polymerization with TiCl,ITHF/MgCl, Catalyst 335

increased linearly with Mg/Ti ratio up to 2.5 as shown in Figure

8. However, activity does not change Mg/Ti ratio between 2.5 and

11, then started to increase at the Mg/Ti ratio above 11. These

results indicate that the polymerization activity is enhanced by

the presence of the comonomer below Mg/Ti ratio of 2.5. The

increase of the catalytic activity by the presence of 1-hexene is

greatest at the lowest Mg/Ti ratio, Mg/Ti=0.42. No cOmOnOmer

enhancement effects in the polymerization activity are appeared

above Mg/Ti ratio of 2.5. ~- Effect of Precipitation condition on the Homo-and ~ 0 -

polymerization of ethylene. Each catalyst prepared at different crystallization temperatures shows a characteristic kinetic pro-

file in homopolymerization of ethylene and copolymerization of

ethylene with 1-hexene due to the different chemical composition.

The profiles in the homopolymerization of ethylene are shown in

Fig. 9. The activity of catalyst decreases as the Mg/Ti ratio of

catalysts decreases. In addition, all catalysts have consider-

able induction times, as it were, the polymerization rates reach maximum after 15 - 30 min. The shorter the induction times, the

larger the Ng/Ti ratio of catalyst is. This result may be come from the difference of activation process of Ti surface sites

distributed onto Mg complex solid matrix. Catalysts of lower

Mg/Ti ratios are in the form of larger crystals due to incomplete heterogenity as discussed in p r e v i m s section. Therefore, they

needed longer time to be grinded to primary particles 8 00

6 00

400 .- I- al

'=- a 2 2 0 0

0

Mg/ T i Figure 8. Average polymerization rate F p ) of (a) ethylene homo-

polymerization and ( b ) ethylene copolymerization with ,l-hexene

with different Mq/Ti ratio.


from which polymer chains grow during the early polymerization

period. The rate profile of the catalyst washed with the solu-

tion of excess AIEtp (KI11) is different from that of the cata-

lyst not washed with AlEt, (see Fig. 9 ( b ) and (e)). The former

was already partially activated with AlEt,, resulting in the

shorter time to reach the maximum rate. However, the average

polymerization rate increased slightly. This indicate that THF

was removed by the reaction with AlEt, during the initial stage

of polymerization. Hence, the rate profile after the prolonged

time of polymerization will be same whether THF is removed before

polymerization or not. As the Mg/Ti ratio of the catalyst increases, the Ti anions

are more evenly distributed onto catalyst surface in the form of

isolated, octahedrally coordinated ions. This indicates that an

excess of Mg compound with respect to Ti compound implies usually

the heterogeneity of the catalyst'). The distribution effect of

Ti anions can be estimated by comparing Fig. 9 and Fig. 10, in which the rate of polymerization is normalized to kg PE/g-Ti hr. The difference of productivity based on the gram of catalyst

(Fig. 10) was not significant in comparison with the difference

of productivity based on the Ti atom of catalyst (Fig. 9). It

may be concluded from this result that Ti anions can be utilized

more effectively as the Mg/Ti ratio of catalyst increases.

Fig. 11 show the kinetic profiles of ethylene copolymeriza-

tion with 1-hexene. No significant induction times were appeared by the addition of 1-hexene. This indicates that 1-hexene in

reaction medium accelerates the initial activation of catalyst

surface sites by the formation of new active centers due to the

coordination of 1-hexene to the initial active centers. After

reaching maximum quickly, the polymerization rates starts to

decay. The decay rate increases as the Mg/Ti ratio increases at

the same concentration of 1-hexene. Therefore, average copolym-

erization rates over an hour do not show large difference as in

the case of homopolymerization. The percentage of crystallinity

of homopolymer (71 % ) determined by heat of fusion decreased con-

siderably by the incorporation of 1-hexene. The crystallinity of

copolymers produced by KI02, KI03, and K104 catalysts with

intermediate Mg/Ti ratios showed similar crystallinities (53 - 5 4

% ) , but copolymer by KIOl catalyst in excess Mg/Ti ratio (11.87),

had much lower crystallinity (50.3 % ) . From above results, it

can be confirmed that reactivitv of 1-hexene is hiuh at excess

26. Olefin Polymerktion with TiCI,ITHFIMgCl, Catalyst 337

300

L

c

I- .-

Fig. 9. Ethylene

polymerization at

70°C, PCzHa-3.0 atm,

and Al/Ti=128 by ( a )

K107 catalyst, (b)

KI08, (C) KI09, ( d ) KI10, and (e) KI11.

- I\, ' Fig. 11. Ethylene

-I '\ copolymerization I \

I \ a I \

.I \ with 1-hexene:

12

s a

0 x 4 ti a

0

Fig. 10. Polymeriza-

tion rate profiles

normalized to the

gram of catalyst.

Polymerization con-

ditions and captions are same as those in

Fig. 9 .

338 I. Kim, M. C. Chug , H. K. Choi. J. H. Kim and S. I . Woo

Mg/Ti ratio.

DISCUSSION

The catalysts of the present study were prepared by dissol-

ving MgC1, and TiC1, in THF, followed by precipitation. During

the dissolution of MgC1, in THF, MgCl,(THF), was

TiCl,(THF), complex was also formed between TiC1, and THF5'".

TiC1, + 2THF ___+ [TiCl,(THF),] (2)

Reaction between MgC12(THF)z and TiCl,(THF), in THF yields a

yellow Mg-Ti bimetallic salts. The crystal structure of these salts has been elucidated at the different molar ratio of

Mg/Tis - ) . However, the formation of discrete chemical complexes between Mg complex and Ti complex may not be a necessary condi-

tions to obtain a highly active catalyst. In the reaction

between TICl,(THF), and MgCl,(THF), the former prefers to form

C1- anion complex due to its strong Lewis acidity. Therefore,

TiC1.(THF)2 removes C1- from MgCl,(THF), to form [TiCl,(THF)]-

anion. The magnesium atom in THF solution under TiC1, treatment

could produce the following cations depending on the molar ratio

As the concentration of MgCl,(THF), in the reaction mixture

increases dimeric Mg cationic complex is easily formed, because

MgC1, is the C1' donor, and MgC1' the acceptor.

The catalysts at a low Mg/Ti ratio, KIO1, KI02 and KID3 cata-

lyst, are expected to be strong ionic complexes. This can be

suggested from the results based on the shift patterns of IR bands (Table 3) and the x-ray diffraction pattern (Fig. 3). The

degree of shift to lower frequencies in IR bands of asymmetrical and symmetrical C - 0 - C stretching bands of THF increases as the

Mg/Ti ratio of the complex decreases. It indicates that stronger

ionic complex is formed at a low Mg/Ti ratio. THF complexed as

TiCl;(THF) must donate electrons of lone pairs in oxygen atom to

Ti atoms to maintain anion, resulting in the largest red-shift in

the C - 0 - C stretching band in THF. The x-ray diffraction patterns

of the catalysts were completely different from those of anhy-

drous MqC1- and MaC1-ITHFI-. The strona 28 reflections at 11.0".

of Mg/Ti: [Mg(THF),]l+, (MgCl(THF),]', and [Mgz(~-Cl),(THF),I''.

26. Okfin Polymerizarion with TiC141THFIMgC12 Cotnlyst 339

17.9" with complicated shoulders, 21.0", and 35" in the catalysts

may be related with the formation of strong ionic complex with a

defined structure.

The ionic character of constituent complexes matrix has a

significant effect on the morphology. The cationic Mg complex

interacts with anionic Ti complex to form cluster bound strongly

each other. In KIO1, KI02 and K103 catalyst of low Mg/Ti ratio,

the size of clusters are large, because the extent of crystal

growth through the regular packing of Mg cation complex and Ti

anion complex occurs via the strong coulombic interaction (Fig.

4). The particle size of the catalysts ranges 100-500 pm. There-

fore, the catalysts needed some time to be disintegrated or frag-

mented to subparticles by the polymer generated at the surface of these subparticles, during the early polymerization time. As can be seen in Fig. 6, 30 to 60 min of induction time is needed for

catalyst KIO1, KI02 and KI03. Considering the average rate of

polymerization catalyzed over these catalysts, only a little titanium in the catalyst are activated for the polymerization.

It means that most of all active sites are occluded in the cata-

lyst matrix because of the difficulties in the fragmentation due

to the strong binding. The strongly coagulated catalysts formed

by the interaction of Ti anion with Mg Cation are difficult to be

disintegrated into the occluded subparticles. Accordingly the

number of polymerization center activated during polymerization is reduced.

The large particle size of KIO1, K102 and K103 catalyst and

less degree of disintegration leads to large polymer particles as

shown in Fig. 12. The average particle size of polymer prepared

with KIO1, K102 and K103 is 750, 630, and 550 pm, respectively. The copolymerization of ethylene with 1-hexene using KIO1,

K102 and K103 catalyst showed considerably different rate pro-

files from those of homopolymerization (Fig. 7). It is very sur-

prising that these catalysts are more active in the copolymeriza-

tion than in the homopolymerization by two or three times (Fig.

8). In addition, the time to reach the maximum rate (induction

time) is much reduced upon the addition of 1-hexene. Many authors have explained the possible causes of the rate

enhancement due to the presence of comonomer l o - l l l . Taking

account of the degree of rate enhancement and the initial rate

profile in the copolymerization with 1-hexene, it can be said

that 1-hexene promotes the catalvst Darticles to be disinteurated

340 I. Kim, M. C. Chung. H. K. Choi, J. H. Kim and S. I. Woo

100

4c 5 0

0

Particle s ize . pm

Figure 12. Particle size distribution of as-nascent polyethylene prepared with ( a ) KIO1, ( b ) KI02, (c) KI03, ( d )

KIO4, (e) KI05, and (f) KI06.

into subparticles. The shorter induction time to reach the

maximum rate must be due to the faster activation of titanium anion complexes into polymerization center. The smaller size of

cluster enhances the diffusion rates of monomer and AlEt,, which

will be reflected in the shorter induction time. However, with

K106 or K105 catalysts where cluster size is only one tenth of

KIO1, the enhancement effect of 1-hexene is not large as in the case of KIO1. Other possibility for the enhancement effect of

1-hexene in the early stage of polymerization might be the

increase of ethylene concentration on the catalyst particles due

to the formation of amorphous part incorporated by the 1-hexene

unit as reported already by Soga et all2).

As the Mg/Ti ratio of the catalyst increases above 2

[TiCl,(THF),]- anions are diluted by MgC1, THF complex matrix.

The matrix is expected to be composed of dimeric Mg cation,

[Mgn(p-C1),(THF),l+, and unreacted MgClZ(THF), due to the

stoichiometry of Mg/Ti. As the Mg/Ti ratio in TiCl4/THF/MgCl1

complex increases, the ionic character of the complex is dimin-

ished due to the dilution bv neutral, unreacted MqCl-fTHF)-. The

26. Olefin PolymnGatim with TiCI,ITHFIMgCl, Catalyst 341

[TiCl,(THF))- anions may be distributed more evenly in the

unreacted MgC12(THF), matrix with Mg/Ti ratio and stabilized by

neighboring dimeric Mg cations. The degree of shift in C - 0 - C

bands of THF decreases as the degree of dilution of Ti anions

increases, i.e. as the Mg/Ti ratio of the catalyst increases, as

shown in Table 3.

Catalysts with intermediate Mg/Ti ratio, K104 and K105 Cats-

lyst , showed some differences in 28 reflections from those with low Mg/Ti ratio, K I O l or KI02 catalyst. The strong 20 reflec-

tions were appeared at 11.0" and 17.9" without any complicated

shoulder. This 29 reflections may be related with the weak ionic

character of the catalyst. KI06 catalyst with highly excess

Mg/Ti ratio, 16.5, showed the same 20 reflections with those of

MgCl,(THF),. It says that [TICl,(THF)]- anions are highly diluted by unreacted MgCl,(THF), matrix. The disappearance of

yellow color in the complex may be another indication of the

dilution.

[TiCl,(THF)]- anions other than those involved in the

lattice, which have a charge opposite to the charge of the Mg complex cation, may cause agglomeration. However, the strength of agglomeration becomes weak as the Mg/Ti ratio of catalyst

increases, because the relative concentration of ion decreases.

As can be seen in Fig. 5, K105 and K106 catalysts are build-up of small and uniform subparticles. The particle size of the cata-

lysts ranges between 50 and 200 pm.

During the early polymerization period, the catalysts,

agglomerates of weakly-bound subparticles, are easily disinte-

grated to subparticles to form a polymerization center, so that only a short time is needed to reach the maximum rate. K105 cata-

lyst (Mg/Ti - 5.2) has a induction period of about 10 min and

K106 catalyst (Mg/Ti = 16.5) only 3 min. The catalytic activity

of the catalysts are about an order of magnitude higher than that

of the catalysts with low Mg/Ti ratio (KIO1, K102 or K103 cata-

lyst). The higher activity comes from a better utilization of

the Ti anions in forming the polymerization centers, in other

words, much more amount of Ti anions existed in the catalyst is

utilized for the formation of active centers. It can be con-

cluded from the morphology of KIO5 and K106 catalyst and the rate

profiles of homopolymerization that no diffusion limitation of

monomer and AIEtl occurs in these catalysts. The small subpar-

ticles and easv disintesration of the catalvsts lead to small

342 I. Kim, M. C. Chung. H. K. Choi. J. H. Kim and S. I. Woo

polymer particles. Expectedly, the particle size of polymer

decreases as the Mg/Ti ratio of the catalyst increases. The

average particle of polymer synthesized by K105 catalyst is 380

um and that by K106 catalyst is 110 vm (Fig. 12).

For K105 and K106 catalyst no enhancement of rate was found

for the copolymerization of ethylene with 1-hexene, different

from the KIO1, K102 or K103 catalyst of low Mg/Ti ratio (Fig. 8).

However, the induction time of the copolymerization becomes short

by the presence of 1-hexene. It indicates that 1-hexene in reac-

tion medium accelerates the initial activation of Ti anion sites

as in the case of the copolymerization using catalysts of low

Mg/Ti ratios. After reaching the maximum rate in a few minute,

the polymerization rate starts to decay.

In the copolymerization using KIO1, KI02 or K103 catalyst

1-hexene in the reaction medium activates the occluded Ti anion

sites in the catalyst, thus increases the number of active poly-

merization centers. However, Ti anion sites in KI05 or K106 cata-

lyst of excess Mg/Ti ratios are activated without the help of

1-hexene, because the formation of active centers is very rapid

due to the smaller size of catalyst subparticles. All the exist-

ing sites which can be activated by the diffusion of monomer and

AIEtp can be activated without the participation of 1-hexene in

the reaction medium. Therefore, the introduction of 1-hexene into

the polyethylene chain decreases the catalytic activity due to

the lower reactivity of 1-hexene. The amount of introduction of

1-hexene in the polymeric chain does not show much difference

according to the Mg/Ti ratio of the catalyst. The density of

copolymers produced are in the range between 0.94 and 0.95 g/cm’

for all catalysts.

ACKNOWLEDGEMENTS

The authors thank the Ministry of Science and Technology in

Korea for granting us research fund (N02710, N03710, and N04900).

We are also grateful to Honam Oil Refinery Co. for assistance in

the PSD and SEM analyses.

REFERENCES

1) A.Greco, G.Bertolini, and S.Cesca, J.Appl.Polym.Sci.,G.

2) ~ . ~ . K a r o l , J.Catal.Rev.-Sci.Eng., 26, 557(1984). 3) U.Giannini. E.Albizzati, S.Parodi, and F.Pirinoli.

2045(1980).

26. Okfin PolymwLathn with TiC141THFIM&12 Cahlyst 343

u.S.Patents 4,124,532(1978).

and S.Parodi, Z.Anorg.Allg.Chem., 482, 121(1981); 496, 205(1983).

5) P.Sobota, J.Utko, and Z.Janas, J.0rganomet.Chem.r 316,

6 ) P.Sobota and J.Utko, Polymer Commun., 2, 144(1988). 7 ) F.J.Karo1, K.J.Cann, and B.E.Wagner,"Transition Metals and

4) J.C.Bart, I.W.Bassi, M.Calcaterra, E.Albizzati, U.Gianini,

19(1986).

Organometallics as Catalysts for Olefin Polymerization", Springer-Verlag, Berlin, (1988) pp. 149.

8) I.Kim and S.I.Woo, Polym.Bull., (1989), in press.

9 ) D.A.Skoog and D.M.West, "Analytical Chemistry", Saunders Col-

10) A.Munoz-Escalona, H.Garcia, and A.Albornoz, J.Appl.Polym.Sci.

11) P.J.T.Tait, "Transition Metals and Organometallics as

lege, Pholadelphia, (1980) pp 581.

- 34, 977(1987).

Catalysts for Olefin Polymerization", Springer-Verlag, Berlin, (1988) pp. 309.

995(1989). 12) K.Soga, H.Yanagihara, and D.H.Lee, Makromol.Chem., 190,


345

27. Morphology of Nascent Polypropylene Produced by MgC12 Supported Ti Catalyst

Masahiro Kakugo, Hajime Sadatoshi, Jiro Sakai

Chiba Research Laboratory, Sumitomo Chemical Co. Ltd., 5-1 Anesaki

Kaigan, Ichihara, Chiba, 299-01, Japan.

Introduction

Ziegler-Natta polymerization using heterogeneous catalyst is the

only commercial process for the production of highly stereospecific

polypropylene, in which &Tic13 and MgC12-supported Ti catalyst are mainly used. In previous papers we studied the architecture of

nascent polypropylene prepared with Tic13 catalysts by transmission

electron microscopy using a newly developed staining method and small

angle X-ray s~attering.~’~,~ In the initial stage of polymerization,

the original catalyst breaks into crystallites whose size is in good

agreement with that of the original crystallites. As the

polymerization proceeds, the crystallites disperse throughout

polypropylene and the primary polymer particles containing one

catalyst crystallite become visible. The primary polymer particles are much smaller than the polymer globules observed on the surface of

the nascent polypropylene. From these findings, we concluded that

the polymer globules on the surface are secondary polymer particles

consisting of some tens of primary polymer particles.

In the present work, we have examined the microstructure of nascent

polypropylene and propylene-ethylene impact copolymer produced by

MgC12-supported Ti catalyst and Mg-Ti .catalyst widely differing in polymer yield using electron microscopy.

Experiment a1

Catalyst Supported catalyst was prepared as follows. MgC12 as a

support was synthesized from n-butylmagunesium chloride and SIC14 then treated with ethyl benzoate. The support thus obtained was

treated with Ti(OR)0,5Cl3.5 (OR: o-cresoxy).

346 M. Kakugo. H. Sadatoshi and J. Sakai

Mg-Ti catalyst was synthesized by reducing titanium tetrabutoxide

with n-butylmagnesium chloride in the presence of silicon

tetraethoxide, and treating with diisobutyl phthalate and then with a

mixture of TiC14, dibutylether, and diisobutyl phthalate. Preparation of &Tic13 has been described previously. 1

Polymerization Propylene polymerization was carried out in

liquefied propylene or heptane. The polymerization was terminated by

flashing out propylene. Propylene-ethylene impact copolymer was

synthesized by two-step polymerization. At the first step polymerization was carried out in liquefied propylene and after

propylene was evaporated, polypropylene was taken out i-n an argon

atmosphere. At the second step a part of the polypropylene

(propylene prepolymer) thus obtained was placed in the autoclave then

an ethylene-propylene mixture was fed and polymerized in gas phase.

WAXD WAXD measurement was carried out with a Shimadzu X-ray diffractometer VD-2 using a scintillation counter and a pulse height analyzer. Ni-filtered CuKa radiation was used. The crystallite size

of MgC12 was calculated from the line breadth of the diffraction

peaks, (003) at 2 =15.O0and (110) at 50.l"lines. The calculation of the crystallite size of TIC13 has been reported

previously. 1

Electron Microscopic Observation The polymer samples for SEM

observation were coated with platinum by a conventional sputtering

technique. The samples for TEM observation were immersed in purified 1.7-octadiene at room temperature in an atomosphere of argon for 2 h. After filtration, liquid 1,7-octadiene on the surface of the samples

was removed by flowing argon for ca. 10 min. Then the samples were

stained over 1% aqueous solution of Os04 for 3 h at 60 "C and sectioned at -80°C by means of ultramicrotome equipped with a glass

knife. The sections were 500 to 1000 in thickness. The specimens

were examined in a Hitachi H-500 electron microscope.

Results and Discussion Architecture of nascent polypropylene The catalysts subjected to

the present experiments are listed in Table 1; the dimensions of the

27. Morphologv of Nacenf PP Prepared with MgC12 Supported Catalyst 347

Table 1. Characteristics of catalysts Average particle Crystallite Composition

Catalyst size,a) pm size,b) Ii TilMgIC1 , wt% Mg-Ti 27 65c) less than 30d) 2/21/68

supported 12 4OC) 30d) 2.5120165

&Tic1 -, 19 108e) 18sd) 2810162 a) Determined by a sedimentograph with decaline as the disperse

medium. b) Determined by WAXD. c) Dl10, length of the primary catalyst crystallites normal to the (110) plane. d) D003, length of the primary catalyst crystallites normal to the (003) plane. In the case of Mg-Ti catalyst Do03 was too small to obtain a clear diffraction peak on the present catalyst. This value was estimated from the experimental evidence that when Do03 was more than 30 A, the clear diffraction peak was obtained. length of the primary

catalyst crystallites normal to the (300) plane. e) D300,

Table 2. Polymer samples Po 1 ymer iza t ion

TiIAlldonor. Temp., Time, Press., Yield

Sample Catalyst mol/L "C h kg/cm2 gige) A-1 Mg-Ti 0.05916. 7a)/l.0c) 45 0.17 22f) 1200

A-3 Mg-Ti 0.0019/1.3a)/0.20c) 70 2 31f) 10100 A-2 Mg-Ti 0.01514. la)/0.71c) 60 1 26f) 3000

A-4 Mg-Ti 0.0015/1. 2a)/0, 17') 80 2 38f) 20500 A-5 supported 0.010/4.4a)/0.96d) 70 1.5 7g) 8000 A-6 6-TiC1, 0.15/13b)10 65 5 2gf) 2030

a)Al(CzH5)3. b)Al(C2H5)2Cl. c)Phenyl trimethoxy silane. d)Methyl p-toluate. e)g of polypropylenelg of catalyst. f-g) Polymerization was carried out f)in propylene, and g)in heptane.

catalyst crystallites are also shown. The polymer samples are shown in Table 2. The surface and inner structures of representative polymer samples prepared with each of the catalysts are shown in Figures 1 and 2. The similar surface structure, agglomerates of the fine polymer globules with a diameter of about 1 ,um can be seen in

Figure 1. Figure 2 shows the internal structure observed by TEM, where a number of the polymer sub-particles can be observed. In the case of sample A-6, each of the polymer sub-particles contains a

348 M. Kakugo. H. Sadatoshi and J. Sakai

nucleus near the center. As noted previously, we concluded that

these sub-particles are the primary polypropylene particles and the

nuclei are catalyst crystallites. In samples A-4 and A - 5 , one can

see the polymer sub-particles containing one or some nuclei with a

diameter of about 50-150 A. Judging from their size, these nuclei

are considered to be MgC12 crystallites.

2 Pm U

A-4 A- 6 Mg-Ti catalyst d -TIC13

Figure 1. SEM photographs of the surface of samples A-4 and A-6 .

0.2 p m U

A-4 A- 5 A-6 Mg-Ti catalyst Supported catalyst d-TiC13

Figure 2. TEM photographs of samples A-4 , A-5 and A - 6 .

27. Morphology of Nacent PP Prepared with Mgclz Suppmied Catalyst 349

Furthermore, we observed samples prepared with the Mg-Ti catalyst

varying in polymer yield. Figure 3 shows the electron micrographs of samples A-1 through A-3. At the low polymer yield (sample A-1) the

polymer sub-particles containing some catalyst nuclei are visible.

As the polymerization proceeds (samples A-2 and A-3) the size of polymer sub-particles increases and the number of nuclei decreases. At the polymer yield of 10100 g of polymer/g of catalyst (sample A-3)

many polymer sub-particles 0 . 3 - 0 . 4 pm in diameter containing a

catalyst crystallite near the center become visible. In samples A-3

and A-4, it is also noticeable that about 50-150 %, particles, which are considered to be catalyst crystallites from their size, can also

be observed near the boundary of sub-particles. The growth of

polypropylene with Mg-Ti catalyst is similar to that with Tic13

except for the number of catalyst crystallites in the polymer sub-

particles at the low polymer yield and the presence of the catalyst

crystallites near the boundary at the high polymer yield.

A- 1 A- 2 A- 3 0.2 pm U

Figure 3 . TEM photographs of polypropylene growth.

Next, the average size of the polymer sub-particles are plotted as a function of polymer yield on logarithmic graph paper in Figure 4.

It has been shown in the case of the Tic13 catalysts that the primary

polymer particles grow surrounding the primary catalyst

~rystallite.~,~ When this view is also valid for the Mg-Ti catalyst,

an average diameter of the primary polymer particles (D) can be

350 M. Kakugo, H. Sadatoshi and J. Sakai

calculated from that of the catalyst crystallites (d) and the polymer yield (Y, g of polymer/g of catalyst) by the following equation:

where Pcat is the density of the catalyst crystallite and Ppp that of polypropylene. A value of 2.3 g/cm3 is taken as Peat for MgC12 and 0.9 g/cm3 as Ppp. The size of the primary polymer particles calculated from this equation is also shown in Figure 4. The observed average size is about 2.5-fold larger. than that thus calculated, but the slope is close to 1/3.

D = d ( ( Pcat Y / Ppp) + l)ll3

i i t 0 0 c

I L

10’ I 0‘ 1 o5

polymer y i e l d (g-PP/g-cat)

Figure 4. Relationship between the size of primary polymer particles and polymer yield. The solid line is the calculated relation. The arithmetic mean of Dl10 and Do03 was taken as the size of the catalyst crystallites. A

value of 30 8, is taken as D110.

From these results we have concluded that the present catalyst consists of highly and less active crystallites and the polymer subparticles observed in samples A-1 through A-4 are primary polypropylene particles which chiefly grew on highly active ones. At the high polymer yield the less active catalyst crystallites are located near the boundary of the primary polypropylene particles.

Architecture of impact copolymer Polymer samples are listed in Table 3 . The TEM photographs of impact copolymer differing in EP

27. Morphology of Nacent PP Prepared with MgcIz Suppotted Catalyst 351

Table 3. Pro py 1 ene - e thy 1 ene impac t cop0 1 yme r s amp 1 e sa

C2IC3, b, Press., Temp., Time, EP yield,')

Sample mol /mol kg/ em2 "C h glg B- 1 301 70 5.9 60 0.17 0.25 8- 2 30170 6.0 60 0.75 1.2 B-3 301 70 5.9 60 5.3 4.2 a) Sample A-1 in Table 1 was used as the propylene prepolymer.

b) Monomer composition; ethylene/propylene. c) EP copolymer yield;

g of EP copolymer/g of propylene prepolymer.

B- 1 8-2 0.2 pm

8-3 U

Figure 5. Transmission electron micrographs of the impact copolymer.

yield are shown in Figure 5. SEM and TEM photographs of the propylene prepolymer are shown in Figure 6. At the low EP yield (sample B-1) the inner structure is similar to propylene prepolymer, sample A-1. In sample B-2 the aggregates of unstained particles and the dark stained bounds can be seen. The size of aggregates is about 0.5-1 ,urn in diameter close to that of the polymer globules on the surface of the propylene prepolymer observed by SEM. Some fibrils among the aggregates can also be seen. At the high EP yield (sample B - 3 ) the unstained particles can be seen, about 0.2 p m in diameter, dark stained bounds and many fibrils among the particles. The size of unstained particles hardly changes in the course of EP polymerization and is almost the same with that of the primary particles in the propylene prepolymer. As previously described on


the morphology of propylene-ethylene impact copolymer, EP part can be observed by the present TEM method.6 Therefore, the dark stained

bounds are considered to be EP copolymer. This result shows that the

major part of EP copolymer polymerized on the surface of the catalyst

crystallites contained in the primary polypropylene particles

transferred to the boundary.

2 Clm 0.2 pm SEM U TEM U

Figure 6 . Electron micrographs of the propylene prepolymer.

The variety in the morphology of the nascent impact copolymers can

be considered to result from the distribution of the aggregation

force in propylene prepolymer: that is, EP copolymer locates in the

weaker boundary. Figure 5 shows that EP copolymer first migrated to boundary among the secondary polymer particles, and then in the

boundary of primary polymer particles. This result supports our

previous conclusion which was obtained by etching a nascent

polypropylene particle with n-heptane: that is, secondary particles

consist of firmly bound primary polymer particles and polymer

globules are secondary polymer particles. The fibrils in samples B-2 and 8-3 are considered to be formed by cold-drowing the crust of the

primary polypropylene particles, due to the effusion of a large

amount of EP copolymer to the boundary.

In conclusion, schematic models for polypropylene and propylene-

ethylene impact copolymer are illustrated in Figure 7 . At the initial stage of polymerization the catalyst crystallites are

27. MWphorogY of Nacent PP Prepared with MsCr, Supported CarCrlpt 353

dispersed uniformly within the polymer particles. As the

polymerization proceeds to a certain extent, the primary

polypropylene particles containing some catalyst crystallites are

formed. As the polymerization proceeds further, the size of primary

polypropylene particles increases and the number of catalyst

crystallites in each of the primary particles decreases; eventually the primary polymer particles containing a catalyst crystallite

appear. In the course of polymerization the primary polypropylene

particle grows mainly on the highly active catalyst crystallite, and

the less active catalyst crystallites are excluded and located near

the boundary of the primary polymer particles.

In impact copolymer, the EP copolymer polymerized at the latter stage is not present in the primary polypropylene particles, but in the boundary of the particles, The EP copolymer, thus, forms the continuous phase in nascent polymer particles.

Polypropylene D o l m r y le ld *

B @ -

cat01 Y5t p o l m r globule

primary po lvwowlene part 1 c l e

c a t a l y s t crystal 11 te

Impoc t Cop01 mer EP v l e ld -

Prlmorv polvrrowlene w r t l c l e

Figure 7. Schematic model for polypropylene growth.


References (1) Kakugo, M.; Sadatoshi, H.; Yokoyama, M.; Kojima, K.

Macromolecules 1989, 22, 547-551 (2) Kakugo, M.; Sadatoshi, H.; Sakai, J.; Yokoyama, M.

Macromolecules 1989, 22, 3174-3177 (3) Kakugo, M.; Sadatoshi, H.; Sakai, J.; Yokoyama, M.

Makromol. Chem. 1988, 189, 2589-2594 (4) Graff, R. J. L.; Kortleve, G.; Vonk, C. G.

J. Polym. Sci., Polym. Letter ed. 1970, 4, 735-739 (5) Natta, G.; Pasguon, I.; Giachetti, E.

Chim, e Ind. 1957, 39, 1002-1012

(6) Kakugo, M.; Sadatoshi, H.; Yokoyama, M. J. Polym. Sci., Polym. Letter ed. 1986, 24, 171-175

355

28. Hafnium Based Catalysts for the Polymerization of Olefins

F.Masi, S.Malquori, L.Barazzoni, F.Menconi, C.Ferrero,

A.Moalli and R.Invernizz1.

EniChem Anic S.p.a. - Polyolefins Division, Catalysts

Research - S.Donato Milanese, Milano (Italy).

SUMMARY:

New catalysts based on Titanium and Hafnium derivatives

co-supported on magnesium chloride are actracting more and

more interest for the preparation of olefin polymers and, in

particular, of high density polyethylene (HDPE).

In order to understand the role of Hafnium in determining

the performances of these new catalytic systems, their

behavior is compared with analogous systems containing only

one transition metal (Hf or Ti).

The polymerization of ethylene and higher &-olefins is

reported and discussed with reference to relevant reaction

variables.

1. INTRODUCTION

The increasing interest acquired by MgC12 supported

catalytic systems containing Hafnium in the production of

polyolefins has recently stimulated the research on the

behavior of this metal in polymerization processes. Studies

concerning both heterogeneous and homogeneous

systems demonstrated the capability of Hf-catalyst to

1)

1-3) 4 , 5 )

356 F. Masi, S. Malquori, L. Barazzoni, F. Menconi, C. Ferrero, A. Moalloi and R. Invernizzi

produce high molecular weight polyethylene even if activity

is generally lower than with Titanium. Thus the polymer

produced by a bimetallic catalyst based on MgC12 supported

Hf and Ti should consist of a large amount of moderate

molecular weight polyethylene produced on Ti-active sites

and of a small amount of very high molecular weight

polyethylene produced on Hf-active sites.

The present work describes the main features of these

industrial bimetallic catalysts in order to use them for

producing polyethylenes with different and broad molecular

weight distributions. For this purpose two industrial

bimetallic catalysts were tested in laboratory under

industrial conditions: analogous tests were performed with

similar catalytic systems containing Titanium or Hafnium in

order to clarify the relative importance of the two metals

on the characteristics of the polyethylene.

Finally experiments with 4-methyl-1-pentene were performed

for a better characterization of the active sites.

2 )

2. RESULTS AND DISCUSSION

2.1 Transition metal catalysts

Supported catalytic systems employed in this work are listed

in Tab. 1. Preparation of all catalysts was carried out

starting with MgC12, Ti(OBu)4 and/or Hf(OBu)4, by following

the procedure described in US Patent 4 421 674, Japan Patent

85/110104 and Italian Patent 21 877A (1988). The general

procedure used consisted of the interaction of the MgC12 and

the transition metal derivatives in different ratios and

successive chlorination by the proper amount of

Aluminumalkyl chlorides.

28. Hafnium-&& Catalysts fw the Po l~r iurr ion of Olefins 357

2.2 Polymerization of ethylene in the presence of different

catalytic systems

The polymerization of ethylene has been performed in

laboratory autoclaves under typical industrial conditions in

n-hexane at 12 bar total pressure, using triisobutylaluminum

(TIBA) as co-catalyst either in the absence or in the

presence of ethylbenzoate (EB).

The influence of some important industrial parameters such

as the hydrogen/ethylene ratio, the 1-butene content in the

polymerization mixture and polymerization temperature on the

behaviour of the catalysts, has been evaluated by measuring

polymer productivity after 4 hours, polymer melt flow index

(MFI), shear sensitivity (SS), intrinsic viscosity and

molecular weight distribution.

Polymerization tests, performed in typical slurry industrial

single-stage process, show that for bimetallic catalysts SS

and intrinsic viscosity increase as Hf content of the

catalyst increases (Tab. 2). Under the same conditions the

Hafnium based monometallic catalyst produces PE with higher

intrinsic viscosity than Ti-based catalyst and the specific

activity is about ten times lower than for Titanium.

Molecular weight distributions of PE obtained with two

different bimetallic catalysts indicate that the polymer

produced by PAR 3/4 catalyst, containing a larger amount of

Hf than PAR 15, contains a higher amount of high molecular

weight macromolecules while the molecular weight averages

are rather close (Fig.1).

The increase of H2/C2H4 molar ratio cause8 in general a

decrease of productivity and polymer intrinsic viscosity

(Tab.3). Indeed for the bimetallic catalyst PAR 15,

358 F. Masi, S. Malquori, L. Barazzoni. F. Menconi, C. Ferrero, A. Moalloi and R. Invernizzi

intrinsic viscosity decreases from 2.3 to 1.9 and specific

activity from 225 to 175 when H2/C2H4 goes from 1.2 to 2.0.

A similar effect is observed for the monometallic Catalysts,

but the polymer intrinsic viscosity in the presence of

Hf-catalyst appears much less sensitive to hydrogen (Tab.3).

Indeed this last catalyst produces PE with intrinsic

viscosity ranging from 13.6 to 4.1 dl/g when H2/C2H4 goes

from 0.4 to 3.3, whereas for Ti-catalyst the intrinsic

viscosity drops from 5.2 to 1.25, when H2/C2H4 increases

from 0.1 to 1.3 (Tab.3).The comparison of the hydrogen

response for both intrinsic viscosity (Fig.2a) and specific

activity (Fig.2b) of mono and bimetallic catalysts clearly

indicates a much lower sensitivity of Hf with respect to Ti.

This property is transmitted to the bimetallic catalysts

which show an intermediate behavior with very modest

hydrogen sensitivity in the H2/C2H4 range investigated.

Specific activity of Hf-catalyst is about 1/100 times lower

than that of Titanium depending on hydrogen/ethylene molar

ratio (Fig.2b). Hence, in the case of polymer chain growing

on Hf-carbon bonds, hydrogen also affects the chain length

and activity probably via the same mechanism as originally

proposed for Titanium , but the Hf-carbon bond appears

much less prone to hydrogenolysis.

Addition of EB in a 10/1 mole ratio with respect to Ti in

Ti/Hf/Mg catalysts resulted in a decrease of specific

activity and average molecular weight, while MFI increases

substantially and SS decreases accordingly (Tab.4).

The effect of EB on the molecular weight distribution

(determined by gel permeation chromatography (GPC)) is shown

in Fig.3 for catalyst PAR 3/4. The bimodal distribution,

5 - 7 )

28. Hafnium-Eased Catalysts f m the Polymerization of Olefins 359

observed in the absence of EB, almost disappears by adding

EB up to a EB/Hf = 0.9 (EB/Ti = 2). Consequently the ratio

weight-average versus number-average molecular weight

(Mw/Mn) decreases from 27 to 19. The catalyst based on

Titanium only shows a certain decrease of specific activity

but almost no effect on MFI and SS when passing from EB/Ti =

0 to EB/Ti = 10 (Tab.4).

The addition of EB to the monometallic Hf-catalyst supported

on MgC12 depresses both specific activity and molecular

weight but the effect on specific activity is quite

substantial. An increase in the EB/Hf ratio from 0 to 1

leads to a drop in specific activity from 47 to 11 KgPE/mole

Metal.h.bar while intrinsic viscosity only diminishes from

13.6 to 11.3 (dl/g) (Tab.4). In all cases EB was added to

the catalytic systems before activation with a large amount

of (TIBA) and it is expected to interact with the more

acidic sites before the starting of the polymerization

reaction. In case of Ti-catalyst probably EB associated with

active sites is removed through a competition with TIBA,

whereas this occurs at much lower extent for Hf-sites. A s

seen before in the absence of EB the polymer properties

depend on the composition of the catalyst. This dependence

can be observed not only in the final values obtained after

4h, but also in their time dependence at shorter

polymerization times. Indeed such variation is much more

pronounced with the bimetallic catalyst having the larger

Hf/Ti mole ratio (Fig.4). Such result is in keeping with

kinetic curves of Hf and Ti monometallic catalysts showing

that by increasing polymerization time, specific activity of

Hf-catalyst decreases in a lower extent than for Ti-catalyst

360 F. Masi, S. Malquori, L. Barazzoni. F. Menconi, C. Ferrero, A. Moalloi and R. Invernizzi

(Fig. 5 ) . The Hf-based catalystic system is apprecciably Sensitive to

the temperature; in particular an increase of temperature

from 65°C to 9O'C produces a decrease of intrinsic viscosity

from 11.9 to 7.7 (dl/g), S.A. dropping from 99 to 68

KgPE/ (moleHf ) 1 hours bar ( Tab. 5 , Figg . 6a and 6b 1.

For bimetallic catalyst PAR 15 an increase of temperature

from 70'C to 85'C produces a substantial decrease of SS from

183 to 90 while MFI is maintained quite constant by

adjusting the hydrogen/ethylene ratio: the increase of S.A.

is owed to the decrease of hydrogen/ethylene ratio.

This effect could be explained by observing that Hf-based

catalyst, at higher temperatures, produces a lower amount of

polyethylene with low intrinsic viscosity.

Both Ti-based and Hf-based catalysts are affected by

1-butane content in the polymerization mixture (Tab.6).

As far as Ti-based catalyst is concerned, an increase of

1-butene from 0 to 10 g/1 causes a slight increase in S.A.;

MFI, instead, goes from 1.7 to 9.1 g/lO' reflecting a

certain sensitivity of the Titanium toward chain-transfer

raction with co-monomer. A different behaviour is showed by

Hf-based catalyst: addition of 1-butene from 0 to 25 g/1 to

the reaction mixture is accompanied by a substantial

decrease in the specific activity while intrinsic viscosity

remains almost unchanged.

In case of bimetallic catalyst PAR 15 an increase of

1-butene from 0 to 25 g/1 produces a certain increase of

S.A. and MFI while SS decreases markedly.

These results suggest that at high 1-butene content the

28. Hafnium-Based Cotolpts for the Pol+tion of Olefins 361

bimetallic catalyst behaves like the monometallic Ti-system

bacause in these conditions the amount of high molecular

weight polyethylene produced by Hf-sites is reduced

substantially.

2.3. Polymerization of c-olefins

In the perspective of using catalytic systems containing

both Ti and Hf, even for copolymers preparation, their

capability to polymerize g-olefins was investigated. In

this context some comparative experiments were carried out

dealing with the polymerization of 4-methyl-1-pentene either

in the presence of bimetallic systems or of monometallic

models. The bimetallic catalyst PAR 15 and the monometallic

Ti-catalyst BOR 146 show very similar behaviour as far as

monomer conversion and stereospecificity are concerned but

in the former case higher molecular weights are reached (PAR

15 [ h i ] = 5.09; BOR 146 [%I - 3.64 Tab.7). Monometallic Hf-catalyst, however, shows a lower specific

activity, a very high intrinsic viscosity and a

stereospecificity of about 100%. These results are in good

agreement with data concerning ethylene polymerization,

reflecting the tendency of Hf-sites to give high molecular

weights. Moreover Hf-catalyst seems to be able to polymerize

4-methyl-1-pentene with high stereospecificity.

362 F. Masi. S. Malquori, L. Barazzoni, F. Menconi, C. Ferrero. A. Moalloi and R.. Invernizzi

3. CONCLUDING REMARKS

The data presented allow the following statements:

- Industrial bimetallic catalysts based on Titanium

and Hafnium supported on MgC12 show high activity for

the polymerization of ethylene and an appreciable

activity in the polymerization of 4-methyl-1-pentene.

- The presence of Hafnium in these catalysts allows to

obtain polyethylene with a broad molecular weight

distribution.

- The broader molecular weight distribution can be

associated with a lower tendency of active Hf-sites to

give chain transfer reactions with hydrogen.

- These bimetallic catalysts can allow to approach, with

the one-stage process, polyethylene with molecular

weight distribution comparable to commercial polymers

obtained in two-stage industrial processes. Temperature

is a useful tool for adjusting molecular weight

distribution.

- Hf-based catalyst is able to polymerize an &-olefin

like 4-methyl-1-pentene with high stereospecificity.

28. Hajiiium-Based Cutalpts for the Polymerizotkm of Okfins 363

Acknowledgement

* The work of the present report has been performed

with the scientific cooperation of Professor

F.Ciardell1 at the Dipartimento di Chimica e Chimica

Industriale of the University of Pisa.

** Mr. E.Anesetti, N.Fuffa, R.Mazzei, A.Sorrentino and

A.Vignati of EniChem Anic are gratefully

acknowledged for their experimental assistance.

REFERENCES

1) R.Invernizzi and F.Marcato, Jpn. Pat. 85/101104 (1985)

C.A., 103 (1985) 142527~.

2) F.Masi, S.Malquori, L.Barazzoni, C.Ferrero, F.Menconi,

A.Moalli, R.Invernizz1, N.Zandona, A.Altomare and

F.Ciardelli, Makromol. Chem., Suppl. 15 (1989) 147.

3) F.Masi, S.Malquor1, L.Barazzoni, R.Invernizzi, A.Altomare

and F.Ciardelli, J. Mol. Cat., (1989) in press.

4) W.Kaminsky, M.Miri, H.Sinn, R.Woldt, Makromol. Chem.,

Rapid Commun. 4, 417, (1983).

5) N.Zandona and F.Ciardelli, Proceedings IX AIM Conference,

Bologna, Italy 16-20 Oct. 1989.

6) G.Natta, G.Mazzanti, P.Longi and F.Bernardini, Chim. Ind.

(Milan) 41 (1959) 419.

7) B.M.Grieveson, Makromol. Chem., 84 (1965) 93.

8) V.Zucchini, Adv. Polym. Sci., 51 (1983) 101.

364 F. M

asi. S. M

alquori, L. EIarazzoni. F. M

enconi. C. Ferrero, A

. Moalloi and R

. Invernizzi

I I Id

IL

,

I I I I 1 I I I IF

4

.d

0, r(

0

E

- ctm

OC

-4

c, .rl cn 0 a

E 0

u’u X

I I I I I I I I I

*d

I

f9

I I C 0-

cn u

-

4 4

cnld Cc,

0aJ

kC

F-r

U

Lo R

0

.-la 00

3u

(d

u

Tab 2: POLPMERIZATION OF ETHYLENE KITH DIFFERENT CATALYTIC SYSTEMS (a)

Catalyst H2/C2H4 ( b ) Specific M.F.I. I f ) ss (g) Viscosity (e) Code Act i v i t y

(mole ratio) KgPE/[molelTi+Hf )*h*barl Ig/lO minl (dl/g 1

PAR 3/4 1,s 127 0.08 170 2,66

PAR 15 1,2 225 0,26 76 2,30 N - 1,51

8 , 6 0

a) - Typical industrial polymerization conditions for monostage process :

b) - determined by GC analysis c) - Specific Activity in KgPE/[moleTi*h*bar] d) - Specific Activity in KgPE/[moleHf*h*barl e) - in TCR at 135-C f ) - ASTM-D 1238 procedure "E"

temperature 85 ^C - pressure 12 bar - solvent hesane - Cocatalyst TIBA

g ) - ASTM-D 1238, SS=MIF/MIE

W m m

s

Catalyst Code

Tab 3: POLYMERIZATION OF ETHYLENE WITH DIFFERENT CATALYTIC SYSTEMS (a) -------- Influence of hydrogen ----------

H2/C2H4 (b) Specific Intrinsic Activity Viscosity (e 1

(mole ratio) KgPE/[mole(TitHf)*h*bar] (dl/g 1

a ) - polymerization conditions for test in autoclave : - duration 4 h - b) - determined by GC analysis c) - Specific Activity in KgPE/[moleTi*h*bar] d) - Specific Activity in KgPE/[moleHf*h*bar] e) - in TCB at 135-C

temperature 85 ^C - pressure 12 bar - solvent hexane - Cocatalyst TIBA

r

0

?

Tab 4: PCLPHERILATION OF ETH'ILENE WITH DIFFERENT CATALYTIC SYSTEHS la) -------- Influence of Ethylbeneoate (EB) ----------

Catalyst SB/Ti EBlHf H21C2HI lb) Specific H.F,I. IfI S.S. i g j intrinsic

laole ratic) (role ratio) KqPE/[mo!e(TitHf l W b a r ] lg/IO mini Idliql Code Activity Viscosity i e I

4 7 21 11

n,d. n.d, 13,60 nod, n,d. 10,9G n.d. n,d. 11,3(3

a) - polymerization conditions for test in autoclave : - duration 4 h - b ) - determined by GC analysis c) - Specific Activity in KgPE/[moleTi*h*bar] d ) - Specific Activity in KgPEl~rcleEf*h*Ssrl e) - in TCB at 135'C f) - ASTH-D 1238 procedure "E" g ) - ASTH-D i 2 3 8 , SS:HIF/IIE

temperature 85 'C - pressure 12 bar - solvent hexane - Cocatalyst TI2b

N Fo

W 0) W

0

?

a ] - pclyrericatioa canditizrs fo r t es t i n autoclave : - diiratka C h -

b ! - Specific Activity in KgPEIIicleEfWbari c ) - ASTI-D 1 2 2 procedure 'E'

e l - i t TCE a t l.?!*C

- presstire 12 bar - solvent h e m e - TIBA 3 nrole/l

d l - CSTM-C 1228 , SS HIF:KIE

L

sa

28. Hafnium

-Based C

ohlysts for the PolynrwiZrrtbn of O

lefins 369

a ) - po!jreri:ation ccnditicns for t e s t it autoclave : - duraticz 4 b - b l - Specific Activity in KgPE,"moleTi*b%ar) c j - SFecific Activity i n igPE!lrcleHf:t:barl dj - ASTH-l! 1238 procedire 'EN e ) - ASTH-D i 2 3 8 , SS : IIF!HIE f l - in TC6 a t 135°C

temperature 25 *C - p:essure 12 bar - sc l iec t heiane - TIE1 3 anole/!

Tab 7: POIYHERILATION Of 4-HETHYL-I-PENIENE WITH DIFFERENT CATALYTIC SYSTEMS la)

Catalyst TIBAlTi Duration Conversion Intrinsic Viscosity Ic) Isotactic fraction ( d i Code (role ratio) ih) ( t ) (dl/g! (wt 8 )

_ _ _ ~ ~ ~ ~

PAR 15

BOR 146

142IR

30 27 93,O 5,09

30 21 94,6 3,64

15 (b) 23 80,6 11,36

72,8

71,s

99,l

a) - Polymerization conditions : - soIvent heptane - terperature 25-C b) - TIBA/Hf cj - in decahydronaphtalene at 135OC d) - insoluble in diethylether

r,

?

28. Hafnium

-hed G

ztalysts fm the P

oljwaerhtion of O

Iefins 371

25

PAR 3/4

MW = 350000 . . Mn = 12200

MZ = 2507000

...-.. -

------------- PAR 15

MW = 243000

Mn = 14900

MZ = 2251000

5

0 2 3 4 5 6 7 8

log (Molecular weight)

Figure 1: GPC curves for polyethylenes prepared with PAR 3/4 and PAR 15

372 F. Masi, S. Malquori, L. Barazzoni, F. Menconi, C. Ferrero, A. Moalloi and R. Invemizzi

mu 146 *- 100.0

142 R ----a -_-__

?AR 314 -.-.-+-.-.-

p u 1s .......A,. .... .

----____ ----___ ----____ -a

-9

-A --.- -.._.._ Y

U 1.0,

0.5-

E

I I I

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 HYOROGEN/ETHYLENE ( m o l a r r a t i o )

Figure 2a: The dipendence of intrinsic viscosity on hydrogen/ethylene molar ratio

n

b n

I z ill 10

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 HYOROGEN/ETHYLENE C ma I ar rat i o 3

I I

Figure 2b: The dipendence of Specific Activity of Ethylene Polymerization

on hydrogen/ethylene molar ratio

28. Hafnium

-Based clrtalysts for the Polym

eriurtion of Okfins

373

30

"I 20

15

10

5

n

EB/Ti=O - MW = 350000

Mn = 12200

...-. .. *..

EB/Ti=2 (EB/Hf - 0.9) " * * .

MW = 267000

Mn = 14300

Mz = 2507000 Mz = 2240000

Mw/Mn = 28.7 Mw/Mn = 18.7

I f W 1 = 2 . 7

U

2 3 4 5 6 7 8 I og (Mo I ecul ar weight)

Figure 3': GPC curves for Polyethylenes prepared with PAR 3/4 catalyst at different EB/Ti ratios

374 F. Masi, S. Malquori, L. Barazzoni, F. Menconi, C. Ferrero, A. M d o i and R. Invernizzi

1.00 n - 0 c

\ a U

r

0.10

PAR 15 -0- ?I 314 ---a-

0 0 0

A A

- "------I 0.05 I 3 4

0 I 2 Polymerizati'on time (h)

Figure 4a: Dependence of Melt Flow Index(M1) of Polyethylene

on polymerization time in the presence of differrent catalysts

- 0 I 2 3 4

Po I ymer i zat i on t i me (h)

Figure 4b: Dependence of Shear Sensit ivity of Polythylene

on polymerization t i m e i n the presence

of different catalysts

Z 0

I- [L K a CD

H

m a W Z W A > I I- W

n L 0 13

L

I (D

0 E \ ID Y

. e

\t

-

U

n L 0 n i .- t-

a 0 E \ n, Y

-

U

1 00

50

0

2400

1200

0 0

142 R ...*....A ........ a>

4% %.\

......... ....................... &-.... &. ................................

Ar....

.........................

BOR 146 -0-

0.5 1 1.5 2 2.5 3 3.5 4

POLYMERIZflTION TIME ( h l

Figure 5: Time dependence of Specific Activity of Ethylene

Polymerization for different catalysts

N Po

Q

P h t!

376 F. Masi, S. Malquori, L. Barazzoni, F. Menconi, C. Ferrero. A. Moalloi and R. Invernizzi

100.0.

rr a, \ - D,

5 8 10.0: 2

* v)

>

Fi -'

F z,

.I .o

100

Symbols .a in Tlgura 6..

-. -. a.

-I

-Q-.

' 0 ----____ --.-_ -- ---_ -- - - -__

'U

I

$ 0

3 lo[ , , , , , , , >

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 HYDROGEN/ETHYLENE ( m o l a r r a t i o >

Figure 6a: Dependence of specific activity of ethylene polymerization on hydrogen/ethylene molar ratio for Hf-based cataryst 142/R at different temperatures.

377

29. High Active Ziegler-Natta Catalysts for Homo- and Copolymerization of Ethylene by Supporting a Grignard Com- pound and TiC14 on SiOl

A. Muiioz-Escalona, A. Fuentes, J . Liscano and A. Albornoz Laboratorio de Polfmeros , Centro de Qufmica, I n s t i t u t o Venezolano de Investigaciones Cientff icas (IVIC), Apartado 21827, Caracas 1020A, Venezuela.

INTRODUCTION

Homo- and copolymerization of ethylene a r e receiving considerable

a t t e n t i o n i n the present decade, due t o d i f f e r e n t reasons: poly-

ethylene i s the world 's most used polymer; low linear dens i ty poly-

ethylene (LLDPE) produced by copolymerization of ethylene with high

a -o l e f ins , such as 1-butene, 1-hexene, 1-octene, e t c . , i s one of

the most rapidly growing polymers; p o s s i b i l i t i e s of producing

d i f f e r e n t types of ethylene-propylene copolymers, such as random and

block copolymers, e t c .

Among the c a t a l y t i c systems used f o r homo- and copolymerization of

e thylene, metals supported on s i l i ca a r e indeed the leading cata-

l y s t s i n the polyolef in industry ( 1 , 2 ) . Therefore, the g r e a t amount

of research works appearing i n the t echn ica l and s c i e n t i f i c l i t e ra -

ture i s mainly concerned with t h i s type of system (3). However, i n

s p i t e of the e f f o r t s t o understand how the S i 0 2 f e a t u r e s , such as

surface a rea , pore volume, pore s i z e d i s t r i b u t i o n , e t c . , inf luence

the polymerization a c t i v i t y and even r e s i n p r o p e r t i e s , many questions

a r e s t i l l open t o discussion (4) . This i s p a r t i c u l a r l y t r u e i n the

case of c a t a l y t i c systems based on t i tanium supported

because r e l a t i v e l y fewer works, compared t o Cr/Si02, have been pub-

on Si02,

378 A. Munoz-Escalona, A. Fuentes, J. Liscano and A. Albornoz

lished on this topic (5).

Karol et el, (6) have published an excellent work centering their

attention on how specific physico-chemical features of the chromium

Si02 supported catalysts control polymer molecular weight, molecu-

lar weight distribution, comonomer incorporation and copolymeriza-

tion kinetics, comparing these results with the ones obtained using

MgC12-TiC12 based catalysts. Hsie et al. ( 7 ) review the performance

of different Si02 supported catalysts for ethylene polymerization

including chromium, titanium and vanadium as active metals. The

titanium supported catalysts were prepared by interaction of alkyl-

magnesium compounds with Si02, followed by reaction with TiC14.

similar procedure, but using a solution of dibutylmagnesium- tri-

ethyl-aluminium complex available from Texas Alkyl (USA), was used

by Hoff et al. (8). Instead of alkylmagnesium compounds, Nowlin et

al. ( 9 ) , prepare high active catalyst for LLDPE production by inter-

action of the Grignard compound EtMgCl with silica, and further

reaction with TiC14 in heptane.

on how catalyst composition influences catalyst activities and

sensitivity to comonomer incorporation. Less attention has been

paid, however, to the mechanism on how the morphology of the cata-

lyst influences cataiyst performance, although for a long time it

has been recognized that the catalyst morphology plays an important

role in olefin polymerizations using conventional Ziegler-Natta

catalysts (10). Polymerization reactions with chromium and tita-

nium supported catalysts, using silica as a carrier, do not present

A

These authors focus their attention

29. Olefin polyme*iEation with SiO, Suppmted Catalyst 379

special problems from the morphological point of view when compared

to the conventional Ziegler-Natta ones. On one hand, the porosity

has to be sufficiently high to allow olefin diffusion inward of the

catalyst, in order for the polymerization to take place.

other hand, the size of the polymer growing inside the catalyst, is

much larger than the average pore diameter of the catalyst, causing

it to fracture during polymerization. Taking into account that the

morphology of the catalyst depends, to a great extent, on the type

of silica used as support (ll), one can expect that the silica fea-

tures influence the polymerization activities of the catalyst, pro-

file of the kinetic curves, morphology and other properties of the

resulting polymers.

to be parallel to the surface area of the silicas being used as

carriers (12). It has also been found that catalysts prepared by

supporting titanium on Si02 with greater pore volume, exhibit

greater polymerization activities (13-15), and that, in addition,

chromium deposited on silica gel having large pores, can even pro-

duce polymer with lower molecular weight (14). Furthermore, it

has been pointed

1.7 cm3g-' is necessary for catalyst fragmentation during polymeri-

zation, giving rise to catalysts with the highest activities

(16).

Industrially, olefins polymerization can be carried out in solution,

slurry and gas-phase processes. In the last two technologies, cata-

lyst morphologies are very important

On the

Thus, it has been shown that the activity tends

out that the use of Si02 with a pore volume of

features to be considered

380 A. MU~IOZ-ESC~OM. A. Fuentes, J. Liscano and A. Albornoz

because they can eliminate many problems in plant operations. Thus,

silica supports determine the size, shape, flow properties of the

catalysts and even the productivity of the plant by controlling the

bulk density of the polymer.

slurry, fine polymer particles, produced by small catalyst granules,

can be very difficult to separate from the solvent by centrifugation,

causing plugging of distillation columns used for solvent purifica-

tion, On the other hand, the gas-phase polymerization using fluid

bed reactors, is even more demanding for catalysts with good morpho-

logical characteristics (17). Thus, spherical catalyst particles

with narrow size distribution are needed in order to obtain improved

flow properties which can be easily fluidized and transported in the

plant. Disintegration of catalyst can produce undesirable fine

particles, which can cause problems in plant operation.

In previous papers, we have studied the role played by different

silicas used in the synthesis of high active Ziegler-Natta catalysts

by supporting TiC14 and alkylaluminium compounds (11,18).

work, we deal with the synthesis of catalysts prepared by the inter-

action of BuMgCl in THF with different types of silica, followed by

the interaction with TiC14 in n-heptane.

origin, exhibiting different surface areas, pore volumes and sizes,

and manufactured by different processes were employed as supports.

The catalysts were tested in the homo- and copolymerization of

ethylene with 1-hexene.

characteristics influence catalytic activities, polymerization kinetics,

In the case of polymerizations in

In this

Four silicas of commercial

Special attention was paid to how the silica

29. Olefin POlyrnerLarion with SiO, Suppwted Catai)st 381

comonomers incorporat ion and changes of polymer morphologies during

polymerization.

EXPERIMENTAL

Catalyst preparat ion and cha rac t e r i za t ion

The s i l i c a s

952, and the Crosf ie ld (England) EP-10 and SD-116. They are manu-

factured by d i f f e r e n t processes. Thus the Davison s i l i c a s , having

sphe r i ca l form, are produced by the so-cal led spray-drying process ;

while the Crosf ie ld s i l i c a s produced by crushing cakes of s i l i c a - g e l ,

exh ib i t i r r e g u l a r shape.

Table I . Catalysts were prepared following the scheme given i n Fig. 1.

Before impregnation, s i l i c a s were d r i ed a t 150°C and 600°C under

vacuum i n order t o e l iminate physical ly absorbed water and t o produce

two d i f f e r e n t hydroxyl groups, e .g . bonded and i s o l a t e d r e spec t ive ly .

After the heat treatment, s i l i c a s were suspended i n dry THF and

0.4 M. of BuMgCl i n THF was added dropwise while s t i r r i n g f o r 15 min.

The BuMgCl was allowed t o r e a c t with the s i l i c a during a per iod of

112 - 3 h . a t temperatures ranging between room temperature and r e f l u x .

When the r eac t ion was f in i shed , the excess of THF was f i l t e r e d o f f ,

the s o l i d product washed with more THF and vacuum dr i ed .

s t age , the above product w a s mixed i n dry heptane and 0 . 7 M . of

TiC14 i n heptane was added dropwise.

t u re s ranging from room temperature t o r e f l u x during 112 - 1 112 h .

while s t i r r i n g . After the r eac t ion was f in i shed , the n-heptane was

chosen as supports were the Grace Davison (USA) 951 and

The physical c h a r a c t e r i s t i c s are given i n

I n a second

The mixture was kept a t tempera-

382 A. Munoz-Escalona, A. Fuentes. J. Liscano and A. Albornoe

f i l t e r e d o f f , t h e s o l i d c a t a l y s t washed with more n-heptane and

f i n a l l y vacuum dr ied a t 30°C t o give a free-flowing powder.

s tages were c a r r i e d out i n a dry l a b . i n order t o ensure anaerobic

and anhydrous condi t ions, The supported Mg and T i were determined

by treatment of 0 .3 - 0.5 g of c a t a l y s t with LiB03 a t 900°C during

15 min. followed by a so lu t ion i n 30 m l . of 10% d i l u t e d H2S04.

Mg was determined by atomic absorption using a Varian model AA-5 and

the T i by i t s peroxide using color imetr ic methods with a W spectro-

meter Bausch & Lomb 70 spectronic model.

A l l

The

Polymerization prodecure

The polymerizations were c a r r i e d out i n a 1 L. batch p r o p e l l e r - s t i r r e d

glass autoclave (Buchi, Switzerland) a t 50°C under constant monomer

pressure between 1 - 5 atm. i n n-heptane a s reac t ion medium. The

s o l i d S i 0 2 supported c a t a l y s t sealed i n a g lass ampoule was introduced

i n the reac tor containing 300 m l of n-heptane.

pressurized a t the desired ethylene pressure followed by the addi t ion

of the E t3A1 as co-catalyst i n a r a t i o of (Al) / (Ti) = 30. The

polymerizations were timed a f t e r breaking the ampoule containing the

c a t a l y s t and the polymerization r a t e was determined from the r a t e of

the monomer consumption using a two-burette system as previously

described (18). I n the case of the copolymerizations, the des i red

amount of 1-hexene was f i r s t added t o t h e n-heptane then pressurized

with ethylene and f i n a l l y the co-catalyst E t 3 A 1 , a s previously men-

t ioned. I n order t o follow the change o f p a r t i c l e s morphology during

polymerization a 2.5 L. g l a s s autoclave with a valve f i t t e d t o the

Then t h e reac tor was

29. OIefin porvrnniznrirm with S i a Supported Catalyst 383

bottom of the reactor was used for samples withdrawal. In this case,

the polymerizations were affected when the valve was opened. Details

of these polymerization procedures have been described elsewhere (19).

In addition to the instananeous polymerization rate, an average speci-

fic polymerization rate (ASPR) was also calculated from the total

amount of polymer produced over the entire polymerization time.

Polymer characterization

The polymers were characterized by their compositions, intrinsic

viscosities, crystallinities and nascent morphologies. Copolymer

compositions were measured by IR spectroscopy.

by hot pressing about5Chg.of polymer between aluminium foil at 170°C

and 100 kg x cm-l pressure during 60 s .

they were water-cooled to ambient temperature for about 5 min.

of approximately 10011 thickness were annealed at 106°C under N2 for

168 h. in sealed tubes.

determined by calculation of the Als80/A722 absorption ratio and with

the use of the calibration curve reported by Nowlin et al. ( 9 ) . Vis-

cosimetrics were carried out in Ubbelohde suspended level viscosimeter . The intrinsic viscosities of the samples were determined at 135- - 0.05"C in decalin containing 0.05 wt% of Santonox to avoid

degradation.

lated using the relationship (20) :

Samples were prepared

After removal from the press,

Films

The hexene contents ($1 in m o l % were

+

polymer

From viscosities average molecular weights were calcu-

(dl/g) 4-0.70 1 n I = 6.2 x 10- M,,

Polymer densities of the molded film were measured employing density

384 A. Muiioz-Escalona, A. Fuentes, J. Liscano and A. Albornoz

gradient column technologies, following the ASTM D1505-68 method (21) . The solvents used to prepare the density gradient were toluene and

CC14 covering a density range of 0.8000 - 0.9790 g/ml. All measurements were carried out at 23°C. From the densities, sample crystal-

linities were determined by using the relation:

Pc P - P a

P Pc Pa crystallinity (X) = - x - x 100

where p is the density of the sample and 'a and 'c are the densities

of the amorphous and crystalline phases, taken as 0.85 x m1-l and

1.005 g x m1-I respectively. The ethylene-hexene copolymers were

fractionated by extraction with cool and boiling n-heptane using a

Soxhlet-type extractor described in reference (10).

The nascent morphology of the produced polymer was examined in a

scanning electron microscope (SEM) Philips model SEM 500 using an

acceleration voltage of 20 KV. The samples were coated with a layer

of gold about 20A thickness by sputtering technique to increase sur-

face conductivity, to avoid electrostatic discharges during observa-

tions.

0

RESULTS AND DISCUSSIONS

Catalysts preparation and characterization

As shown in scheme of Fig. 1, catalysts were prepared under a great

variety of experimental conditions. The amounts of Mg and Ti and

consequently the Ti/Mg ratios loaded onto the silica are very sensitive

to the preparation conditions, such as calcination temperatures of

29. Okjin Pol'tion with Si@ Suppwted Catalyst 385

the s i l i c a , concentration of BuMgCl and TiC14, temperatures and times

used f o r the r eac t ions , e t c . Bearing i n mind t h a t the T i / @ r a t i o

s t rongly influences the c a t a l y s t a c t i v i t i e s and r e a c t i v i t i e s towards

the comonomer 1-hexene (9), ca re fu l preparat ions were taken t o assure

t h a t a l l r eac t ion s t eps i n the c a t a l y s t s preparat ion were kept constant

i n the four s i l i c a s . The s i l i c a s were p re - t r ea t ed a t 150°C and 600°C

before impregnation. However, the most a c t i v e c a t a l y s t s were obtained

when s i l i c a s were dr ied a t 600°C under N2 stream during 3 h .

such conditions, less amounts of Mg and T i were supported owing t o

the presence of only i s o l a t e d o r s i n g l e hydroxyl groups.

amount of BuMgCl used l a rge ly exceeds the population of hydroxyl

groups present i n the s i l i c a (about 1 m mol/g f o r s i l i ca 952 d r i ed

a t 600"C), p r a c t i c a l l y a l l hydroxyl groups a r e used i n the r eac t ion .

The f a c t t h a t Grignard compounds are used f o r measurement of hydroxyl

content of s i l i c a can be r eca l l ed t o confirm t h i s apprec i a t ion (23).

Nevertheless, i t can not be t o t a l l y ru l ed out t h a t some hydroxyl

groups remain s t i l l unreactive a f t e r BuMgCl treatment. In t h e second

s t e p , the Mg modified s i l i c a s were reacted with an excess of T i C 1 4 i n

n-heptane. Different temperatures and r eac t ion times were a l s o

employed t o ca r ry out t h i s r eac t ion .

tends t o be p a r a l l e l t o the amount of preloaded Mg. The Ti/Mg r a t i o s

obtained with the four s i l i c a s are given i n Table 11. These r e s u l t s

can be explained by admitt ing t h a t c l u s t e r s of TiC14 were formed

surrounding the Mg atoms, as formulated i n scheme shown i n Fig. 2 .

The Ti/Mg r a t i o s obtained a r e higher than those reported by Nowlin e t a l .

Under

Since the

The amount of supported TiC14


(about 2-3) ( 9 ) , although the c a t a l y s t s products w e r e washed with

plenty of solvents i n each s t e p o f c a t a l y s t s preparat ion.

of vacuum drying a t 100°C f o r 2 h . , T i C 1 4 was d i s t i l l e d o f f and

Ti/Mg r a t i o s decreased t o values of about 2.

r a t i o s e x h i b i t the h ighes t c a t a l y t i c a c t i v i t i e s . Therefore, c l u s t e r s

of T i /Mg -. 2-3 a r e reduced t o c l u s t e r s of Ti'" wi th s imilar r a t i o s

when t r e a t e d with co -ca t a lys t E t 3 A 1 as formulated i n Fig. 2. Under

such condi t ions, Mg atoms inf luence more e f f e c t i v e l y the T i through

t h e chlor ine br idges.

By means

Ca ta lys t s having these

IV -

Homopolymerization of Ethylene

Polymerization experiments were c a r r i e d out t o determine the e f f e c t

of the following f a c t o r s on the c a t a l y t i c a c t i v i t i e s :

temperature, presence of Mg, pore volume and su r face a rea of the

s i l i c a , and monomer pressure.

The e f f e c t of drying temperature and pressure of Mg on the c a t a l y t i c

a c t i v i t y can be seen c l e a r l y by looking a t Fig. 3 f o r polymerization

runs a t 5 atm. monomer pressure. As published before (221, s i l i ca

d r i ed a t 600°C and having i s o l a t e d hydroxyl groups produce c a t a l y s t s

with higher a c t i v i t i e s , compared with those prepared on s i l i c a d r i e d

a t 150°C. In both cases , accelerat ion-type k i n e t i c curves were obtained

with maximum a c t i v i t i e s (Amax) of 2000 and 200 gPE x gTi- l x h-' x

atm. r e spec t ive ly . By loading the s i l i c a previously with Mg before supporting TiC14, cata-

l y s t a c t i v i t i e s d r a s t i c a l l y inc rease . The type of k i n e t i c curves a l s o

change from acce le ra t ion t o decay.

gTi-' x h - l x atm.-' were e a s i l y reached.

s i l i c a drying

A c t i v i t i e s as high as 400 gPE x

The time (tmax) t o reach

the maximum activity decreases as the activity of the catalyst in-

creases, Under such conditions, problems to eliminate the heat of

polymerization were observed. Therefore, it was decided to carry

out the experiments at 1 atm. monomer pressure. At lower monomer

pressure, the kinetic curves change from decay to acceleration. Some

results obtained under such conditions are shown in Fig. 4 and Fig. 5 .

In the case of catalyst synthesized with silica 952 Amax of about

1200 gPE x gTi-’ x h-’ x atm.

time, while only 700 gPE x gTi’l x h-’ x atm.-l was reached with

silica SD-116 dried at the same temperature of 600°C.

make it clear that the porosity strongly influences the catalytic

activities, confirming results found by other authors (16). Catalysts

prepared with silica having a pore volume of 1.7 crn3g-l (silica 952)

exhibit the highest activities.

by assuming that catalysts based on silica with pore volume of

1.7 cm3g-’ undergo fracture and fragmentation during the growth of

the polymer, maintaining the network of the pore and facilitating,

therefore, the transport of the monomer to the active sites.

contrary, catalysts based on silica with higher pore volume (silica

SD-116) have lower activities due to the fact that polymers plug the

initial pore structure, slowing down the monomer diffusion, and

avoiding fragmentation of the catalysts during polymerization.

-1 was obtained after 3 h. polymerization

These results

These results have been explained

On the

Copolymerization of Ethylene with l-Hexene

The presence of l-hexene in the reaction medium causes drastic changes

in the catalytic behaviour of the catalysts, as shown in Figs. 6 and 7 .


The profile of the kinetic curves changes from accelerations to decays,

as the co-monomer concentration increases. The maximum instantaneous

catalyst activity (Amax) gradually increases with the increase in the

l-hexene amount. Concomitantly, the width at half-maximum and the

time (tmax) elapsed when reaching maximum activity decrease. These

facts have been explained by assuming formation of new active centers,

regeneration of deactivated active sites, due to the stronger donor

strength of higher olefins (23) and finally by lower diffusion limita-

tion of the monomers throughout the less crystalline polymer layer

covering the catalyst particles (24, 2 5 ) . Less attention, however,

has been paid to the change of the catalyst morphology due to the

presence of l-hexene.

higher a-olefins modified the fragmentation mechanism of the catalyst,

therefore originating new active centers, modifying catalyst morphology

and growth of the polymer particles during polymerization.

In Fig. 8, the average specific polymerization rate, after 3 h. poly-

merization time, has been plotted against the l-hexene concentration

in the feed.

was obtained with the catalyst synthesized using the silica SD-116

exhibiting the highest pore volume (1.97 cm The lowest acti-

vity was obtained with the silica 951, having a pore volume of 1.00 cm

x g-I.

very important factor in the behaviour of the catalyst for copolymeri-

zation of ethylene with higher a-olefins.

based on silica manufactured by different processes but having similar

As will be discussed later on, the presence of

It can be seen that the highest polymerization activity

3 x g-'). 3

These results suggest, undoubtedly, that the pore volume is a

On the other hand, catalysts

29. Olefin Pol’tion with SiO, Supported Catalyst 389

pore volume such as silica 952 and EP-10, give rise to different be-

haviour in the copolymerization of ethylene with 1-hexene. Thus, at

low co-monomer concentration, silica 952 is more effective than the

EP-10. However, at high co-monomer concentration, the catalysts be-

haviour (0.82 molar) is similar for both silicas, These results could

be possibly due to differences in pore size distributions and pore struc-

ture in both silicas. These features play a decisive role in catalyst

fragmentation mechanism during polymerization, as established by Weist

et al. (15, 16).

It appears also that the sensitivity of catalyst towards 1-hexene could

be controlled by the catalyst porosity. Thus, catalysts based on

silica SD-116 produce copolymers with higher 1-hexene content, as can

be seen in Fig. 9. Very interesting results were obtained by fraction-

ation of the copolymers with heptane, as shown in Table 111. Catalysts

based on silica SD-116 produce the more homogeneous copolymers. Cata-

lysts based on silicas with similar pore volume (EP-10 and 952) pro-

duce copolymers with similar compositional distributions. In general,

the increase in the amount of 1-hexene gives rise to copolymers with

higher heterogeneity in the molecular composition.

Finally, the presence of 1-hexene brings about a decrease in molecular

weight as shown in Fig. 10 and a decrease in the polymer crystallini-

ties (Fig. 11).

Morphological Features

Figs. 12 and 13 show SEM micrographs of silica Davison 952 and Crosfield

SD-116, respectively, which were used for catalysts synthesis. Silica

390 A. Muiioz-Exalona, A. Fuentes, J. Liscano and A. Albornoz

Crosf ie ld EP-10 looks very much similar t o the SD-116.

s i l i c a (Davison 952 and Crosf ie ld) are very d i f f e r e n t i n s i z e and shape,

and i n the in s ide morphology. Davison s i l i c a produced by the so -ca l l ed

spray-drying process are sphe r i ca l i n form and e x h i b i t a broad p a r t i c l e

s i z e d i s t r i b u t i o n , and present l a rge holes i n s i d e . On the o t h e r hand,

Crosf ie ld s i l i c a , manufactured by crushing cakes of s i l i c a - g e l , a r e

i r r e g u l a r i n form but are very uniform i n s i d e .

It has been reported t h a t under appropriate polymerization cond i t ions ,

e . g . c a t a l y t i c a c t i v i t y and i n i t i a l polymerization r a t e , t he polymer

keeps the o r i g i n a l morphology of t h e s i l i ca used f o r c a t a l y s t syn thes i s

(6 , 2 2 ) . Thus, the morphology of t h e produced polymers c lose ly resemble

the morphology of the c a t a l y s t s ( r e p l i c a t i o n phenomena). However, when

the c a t a l y s t s were used f o r homopolymerization of e thylene, no r e p l i c a -

t i o n phenomena were found. The c a t a l y s t s des in t eg ra t ed i n the e a r l y

s tage of t he polymerization, as shown i n Fig. 14 , f o r c a t a l y s t s based

on Davison s i l i ca 952 a f t e r 0 .3 sec. polymerization time.

polymer granules , however, keep the morphology of the parent s i l i ca ,

though exh ib i t i ng very l a rge pores , resembling sponges (Fig. 15). Simi-

l a r r e s u l t s w e r e a l s o obtained with c a t a l y s t s based on Crosf ie ld s i l i c a

(see Fig. 1 6 ) .

down due t o the mechanical stress produced by t h e growing polymer,

losing the a b i l i t y t o con t ro l the polymer morphology. These r e s u l t s

have been explained by admitt ing that the polymerization takes p l ace

very r ap id ly on the ou t s ide of t he c a t a l y s t p a r t i c l e .

crease of the temperature a t the c a t a l y s t su r f ace , t he p a r t i c l e s become

Both types of

Only few

It can be observed t h a t t h e c a t a l y s t s p a r t i c l e s break

Due t o the in -

29. Olefin P o l ~ t i o n with SiO, Supported Cuhlyst 391

hot and soft, disintegrating as a result. Consequently, the polymer

grows on the catalyst subparticles instead of on the particles as a

whole. In the presence of 1-hexene, a rubber-like amorphous layer of

polymer is first formed surrounding the catalyst particles, prevent-

ing them from disintegration and preserving, therefore, the shape of

the original catalyst, The number of disintegrated particles decreases

as the concentration of 1-hexene in the reaction medium increases and

a replication phenomena is observed (see Figs. 17 and 18). The parti-

cles now grow more evenly on the whole catalyst mass and consequently

the polymerization rate becomes higher as the efficiency of the cata-

lyst is improved.

to the deactivation of active species as the polymerization proceeds,

and also to the diffusion limitation as the polymer layer covering the

catalyst particles increases.

The decay of the polymerization rate can be due

392 A. Munoz-Escalona, A. Fuentes. J. Liscano and A. Albornoz

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13

14.

15.

REFERENCES

R.L. Magovern, Po1ym.-Plast. Technol. Eng. 13(1) , 1 (1979).

H.R. Sailors and J.P. Hogan in History of Polymer Science and References Technology Ed. R.B. Seymour. Marcel Dekker, New York 1982; p. 313.

M.P. McDaniel in Advances in Catalysis, vol. 33 Eds. D.D. Eley, H. Pines, P.B. Weisz. Academic Press, New York 1985: p. 47.

A. Ellison, J.A. Moulijn, B. Scheffer, A. Brown, B. Herbert, B. Humphrey, G. Diakun, P. Worthington, F.E. Mabbs and D. Collinson in Advances in Polyolefins. Eds. R.B. Seymour and T. Cheng. Plenum Press, New York, 1987; p. 111.

A. Muiioz-Escalona in Transition Metal Catalyzed Polymerizations. Ed. R.P. Quirk. MMI Press, 1981; p. 323.

F.J. Karol, B.E. Wagner, I.J. Levine, G.L. Greke and A. Noshay in Advances in Polyolefins. Eds. R.B. Seymour and T. Cheng. Plenum Press, New York 1987; p. 337.

H.L. Hsieh, M.P. McDaniel, J.L. Martin, P.D. Smith and D.R. Fashey in Advances in Polyolefins. Eds. R.B. Seymour and T. Cheng. Plenum Press, New York 1987; p . 153.

R.E. Hoff, T.J. Pullukat and R.A. Dombro in Advances in Polyolefins. Eds. R.B. Seymour and T. Cheng. Plenum Press, New York, 1987; p . 241.

T.E. Nowlin, J.V. Kissin and K.P. Wagner. J. Polym. Sci. Part A, Polym. Chem. 26, 755 (1988). J. Boor, Jr. Ziegler-Natta Catalysts and Polymerizations. Academic Press, New York 1979.

A. Muiioz-Escalona, J.G. Hernandez and J. Gallardo in Catalytic Polymerization of Olefins. Eds. T. Keii and K. Soga. Elsevier Science Publisher, Amsterdam, 1985 ; p. 123.

A. Muiioz-Escalona, J.G. Hernandez and J.A. Gallardo. J. Appl. Polym. Sci. 3, 1187 (1984). W.L. Carrick, R.J. Turbett, F.J. Karol, G.L. Karapinka, A.S. Fox and R.N. Johnson. J. Polym. Sci. A-1, 10, 2609 (1972). M.P. McDaniel, J. Polym. Chem. Ed. - 19, 1967 (1981).

E.L. Weist, A.H. Ali and W.C. Connor. Macromolecules 20, 689 (1987)

29. Olefin PolyttwizariOn with SiO, Suppomied Catalyst 393

16. E . L . Weist, A.H. A l i , B . G . Naik and W . C . Connor. Macromolecules. To be publ i shed .

1 7 . F . J . Karol and F . I . Jacobson i n C a t a l y t i c Polymerizat ion o f O l e - f i n s . Eds. T . Keii and K . Soga. Elsevier Science P u b l i s h e r , Amsterdam 1985, p . 323.

i n Advances i n Po lyo le f ins . Eds. R . B . Seymour and T . Cheng. Plenum P r e s s , New York, 1987, p . 179.

18 . A. Mufioz-Escalona, J . G . Hernandez, J . A . Gal la rdo and A. S u s t i c

19. A. Muiioz-Escalona and A. Parada. Polymer 20, 474 (1979).

20. R . J . Chiang. J . Phys. Chem. 6!3, 1945 (1965).

2 1 . ASTM D 1506-68 v o l . 27, Am. SOC. f o r Tes t ing Mater. Ph i l ade lph ia

2 2 . A. Mufioz-Escalona, C . Alarc6r1, L.A. Albornoz, A . Fuentes and J . A .

(USA) 1 9 7 2 .

Sequera i n Ole f in Polymerizat ion. Eds. W. Kaminsky and H . S inn . Spr inger Verlag 1987, p . 417.

23. D . C . Calabro and F. Y . Lo i n T r a n s i t i o n Metal Catalyzed Polymeri- za t ions Zieg ler -Nat ta and Meta thes is Polymerizat ions. Ed. R .P . Quirk. Cambridge Univers i ty Press. Cambridge, 1988, p . 729.

24. A . Mufioz-Escalona, H . Garcfa and A. Albornoz. J . o f Appl. Polym. S c i . - 34, 977 (1987).

25. R.A. Hutchinson and W.H. Ray. So rp t ion E f f e c t s i n Heterogeneous Catalyzed Ole f in Polymerizat ion, Washington (USA), November-December 1988.

Presented a t t h e AIChE Meeting.

26. A . Muiioz-Escalona. To be publ i shed i n Makromol. Chem. Rapid Comm.

394 A. Munoz-Escalona, A. Fuentes, J. L i m o and A. Albornoz

I VACUUM DRIED AT I5O.C OR 600.C)

10.4 mdor in TMFI 6 1/2-3h Room tmmp-rollua T H F t- EuMaCl

F ILTE R ED 1 WASMED I WITH TMF

VACUUM DRIED

(0 .7 molar in kaplond

I h -3h

F I L T E R E D e HEPTANE

Fig. 1 . Schemc for Catalysts Preparation by Supporting B*Cl and TICl,, on Si l ica .

XV Clustrrs Ti / Mg.4

CI ! I,C'

. -ti- \ r \ I . ,Ti-CI

SI 02

hlghly activr CIuSt#rS

Ti"/ Mg 8 2

Fig. 2 . Scheme of Porrible Active Centers Fornution

29. Olefin P o l ~ t i o n with S Q Supported Gatalyst 395

TIME ( h )

Fig. 3 . Ethylrnr Polymrrlzotion SO*C, Satm'., Et3AI I All/ lTI l*30

800 - 0 " c I - 600 s n

4

0 200 L

C. SO- 116-(150*C) Ma-T i I

I- d

0.5 I 1.5 2 2.5 3

TIME ( h )

Fig. 4 . Ethylenr Polymarlzation, 5O.C. lo tm. . Et+i , l A l l IT I l -30


a O

r a

$1500

M 9 5 2 - ( 1 5 0 * C l M g - T I

H 9 5 2 - ( 6 0 0 * C l M g - T I -

* 0.00

0.05 molar + 0.10 molar -0-0- 0.20 molar -m-+ 0.41 molar

-&& 0.82 molar

0 0.5 I I .5 2 2.5 3

T lME(h) Fig. 6 . Catalytlc activity of952(600*C)-M0.Tl catolytr VI. polymrrlzatlon t lmr at d l f f r r r n t

concrntration o f h r x r n r - I . Polymrrlratlan condltlonr 50.C. I otm. Et3AI . A I / T I = 3 O

29. Olefin Polymerhtion with SiO, Supported Cutalyst 397

a z '-6000 N r G g

- 7000

" l=

+ S102 351 -(600*C)-Mg-Ti * SIOz 952- (60OeC)-Mg-TI

- - S102 SD-l16-(600*C)-Mg-T1

-0-0- S102-EP10(600T)- Mg-Ti

a ir . . 4" 5000 - % > L g 3000 a

* 0.00 0.05 molor

tc 0. 10 molor

+ 0 . 2 0 molar

u 0.41 molar

-&&- 0.82 molor

0 0.5 I 1.5 2 2.5 3

TIME ( h )

Fig. 7 . Catalytic activity SD-I16-(6000C)Mg- TI cotalyrtr us. polymrrlzatlon tlmr at d l f f r r r n t con-

centration of h r x r n r - I . Polymrrlrotlm condltlons: 5 0 * C , I otm., EtSAI, A l / T i = 3 0

398 A. M ~ o z - E s ~ o M . A. Fuentes, J. Liscano and A. Albornoz

T A B L E I

CHARACTERIZATION OF SILICA U S E D FOR SUPPORTED BuMpCI/TI C l 4

Z I E G L E R - NATTA C A T A L Y S T S

YANUCACTURER T Y P E SURFACE A R E A P O R E VOLUME AVERAOI w.w SILL

rd.IJ-l, 1cn3xp-l) IX 1 ~ ~~

D A V I S O N 95 I 800 1.00

DAVISON 952 300 I . 70

CROSFIELD EP- 10 330 1.80

CROSFIELD 90-116 350 1.97

T A B L E I1

SUMMARY OF CATALYST CH ARA CTERIZ ATlON

b I SILICA') I Ti /Mg RATIO

65

200

2 35

295

a) SILICA DRIED A T S O O T , 3 h. UNDER N 2

b ) BY R E A C T I O N S A T ROOM T E M P E R A T U R E V Z h A N D W A S H E D W I T H P L E W T Y O F S O L V E N T E S I N EACH STEP.

29. Olefin Polym&zation with SiO, Suppmted Cokalyst 399

12-

9 .

I I I 1 t I

0.2 0.4 0.6 0.8 1.0

1-HEXENE IN FEED (MOLAR)

DEPENDENCE TO THE COPOLYMER AND I-HEXENE CONTENT IN FEED

BE TWEEN 1-HE X EN E INCOR POR ATEQ

FOR THE CATALYST SYNTHESIZED WITH (0) 9 5 2 (600.1-

Mg-TI AND ( 0 ) SD- 116 (6W0C)-Mp-Tl.

T A B L E 1x1

COMPOSITIONAL HETEROGENEITY OF COPOLYMERS

CATALYST COMONOMER FRACTION I. I-HEXENE SOLUBLE IN FEED IN COOL

HE PTA NE

fNr) [ MOLAR 1 rn)

S D - I ~ I N ~ ~ ~ F ) H J - T I 0.206 0.52

SO- IlS(SOO'CIM~-Tl 0.4 I2 0.8 5

SD-118(600F~Mq-TI 0.824 4.08

FRACTION 11 FRACTION I11 SOLUBLE I N SOLUBLE IN BOILING I N 801LING HEPTANE HEPTANE

(76) (%I

1.4 4 98.04

1.90 97.4 5

7.26 88.68

EP-I0 (6OO'C)M-TI 0.206 a 8 3 2.19 9 8 9 8

EP-I0 (6OO'ClMg-TI 0.4 I 2 2.24 5.18 9 2 6 8

EP- lO(SOO*C)Mg-TI 0.824 3.54 17.26 79.20

952- ( 6 0 0 ~ I ~g -n 0.208 0.22 0.85 98.93

952-(60OoC)Mq-TI 0.41 2 1.77 4.43 93.79

962-(60O*Cl Mg-TI 0.824 13.38 15.60 71.02

400 A. MU~IOZ-ESC~~OM, A. Fuentes, J. Liscano and A. Albornoz

-I

2 $!? 20 U 0

10

t-

-

-

-

I 1 I I I I

I I I I I

0.1 0.2 0.4 0.6 0.8 1.0

HEXENE-I (molar)

Fig. lo. Effect of hexrnr - l concentrations on rnolrculor wrlghts (wlthout Hp). 5 0 * C , I a h . A I E t , , 1AI1 IT11 a 3 0

HEXENE-l(molar)

Fig. 11. E f f r c t o f h r x r n r - l concrntratlon on cr is to l l ln i t i r r of producrd L L D P E 5ODC, fotm. , A i E ~ J , I A I I / I T I ~ = ~ O

Fig. 12. Sem micrographs of silica Davison Si02 952. a) General view b) Cross-sectioned.

Fig. 13.Semmicrographs of silica Crosfield Si02 SD-116. a) General view b) Cross-sectioned.

Fig.14.Sem micrographs of PE growing particles at very early polymerization time (0.30 sec.). Catalyst based on Davison Si02, 952 (600°C)-Mg-Ti. 5 atm., 50 'C, A1Et3, Al/Ti=30 in n-Heptane.

Fig. 15. Sem micrographs showing details of growing PE particles at very early polymerization time (0.30 sec.). Catalyst based on Davison SiO 952 (600°C)-Mg-Ti. 5 atm., 5OoC, AlEt3, Al/Ti=36 in n-Heptane.

Fig. 16. Sem micrographs of PE growing particles after 30 sec. polymerization time. a) General view b) Higher magnification. Catalyst based on Crosfield SiO SD-116 (600°C)-Mg-Ti, 5 atm., 50°C, AtEt3, Al/Ti=30.

Fig. 17. Sem micrographs of PE copolymer granules obtained with catalyst based on silica 952 (60O0C)-Mg-Ti at different 1-hexene concentrations: a) 0.05 mol/l. b) 0.824 mol/l.

Fig. 18. Sem micrographs of PE copolymer granules obtained with catalyst based on silica SD-116 (600°C)-Mg-Ti at different 1-hexene concentrations: a) 0.05 moll1 b) 0.824 mol/l.

0

P' %

f. s k? ,o

4 s

402 A

. Muiioz-E

scalona. A. F

uentes, J. Liscano and A

. Albornoz

29. Okfin Polym

niZatimr w

ifh SiO,

Suppmted C

atalyst 403

404 A

. Munoz-E

scalona, A. F

uentes, J. Liscano and A

. Albornoz

405

30. New Solvay SB 12 TiC13 Polypropylene Catalyst

A. BERNARD and P. FIASSE

Solvay et Cie S.A. , Laboratoire Central,

Rue de Ransbeek 310, B-1120 Bruxelles, Belgique

ABSTRACT

There are multiple requirements for a modern coPunercial.polypropylene

production catalyst : catalyst productivity, polymer stereoregularity and

molecular weight control, and powder morphology have to be balanced and

maximized.

is now embodied in the third generation SB 12 catalyst, a product combi-

ning a unique set of the most desirable properties.

the SB 12 catalyst in typical polymerization conditions is detailled.

basic influence of the intrinsic catalyst properties on both polymer pro-

perties and production process is discussed.

The research and development carried out on the TIC13 catalyst

The performance of

The

INTRODUCTION

Since the beginning of the use of Ziegler-Natta catalysts for the

production of isotactic polypropylene, numerous improvements of both pro-

duction processes and product properties were promoted by the dramatic

progress of the catalyst performance. In the industrial manufacture of

polypropylene, four major performance characteristics of the catalytic

system have to be balanced and maximized: the catalyst productivity, the

polymer stereoregularity and molecular weight control, and the powder

morphology.

The catalyst productivity i.e. the number of kg of polypropylene pro-

duced per kg of catalyst and the polymer stereoregularity i.e. the frac-

tion of isotactic polymer in the total produced polymer must be high

enough to avoid the costly catalyst residue and atactic polymer cleanup

steps existing in the conventional PP processes.

cess must be able to produce a broad range of different polypropylene gra-

des by controlling the average molecular weight. The molecular weight

distribution and the tacticity of the polymer must also be in order to

correctly ensure its crystallinity, stiffness and processing properties.

Finally, the economical running of any process requires a careful control

of the morphology of the polymer powder, i.e. mainly the particle size

distribution and the bulk density of the powder.

Moreover, a modern pro-

406 A. Bernard and P. Fiasse

Ball like polymer particles with high bulk density afford high polymer

content in the reactor vessel and thus the highest yield and most favora-

ble economics.

Solvay has been pionnering high performance titanium trichloride

catalyst since 1970.

industrial PP catalyst performance through the commercial production of

the second generation catalyst affording both higher productivity and

stereospecificity. The continuous research effort to improve and extend

the catalyst properties has now led to the new SB 12, third generation

TiC13. This product embodies the latest development in the field and

shows a unique set of the most desirable properties for an industrial

polypropylene catalyst.

In 1977, this work led to the first definite jump in

This paper reviews how a single catalytic system can meet the mani-

fold requirements of a modern industrial polypropylene production process

by detailing the performance of the SB 12 catalyst in typical polymeriza-

tion conditions.

EXPERIMENTAL

Reagents. Propylene and nitrogen are purified.and dried by a

treatment on molecular sieves and finely dispersed metallic copper.

hexane used to suspend the catalyst is distilled and treated the same way.

High purity hydrogen is used without additional treatment.

The

Catalyst. The SB 12 is a non supported catalyst containing about

70 weight percent of titanium trichloride.

liter suspension in dry hexane.

diethylaluminium chloride compound (mDEAC).

percent solution in dry hexane.

control agent.

It is used as a 20 gram per

The cocatalyst used is a modified

It is used as a 10 weight

Hydrogen is used as a molecular weight

Polymerization. The polymerization runs are made in a 5 liter

stainless steel reactor in a bulk homopolymerization. Cocatalyst (5.64

mmol), catalyst (0.2 to 0.5 mmol), hydrogen (0.2 to 2 bar) and liquid pro-

pylene (3:5 liters) are succesively introduced under a nitrogen blanket

and the heating to the polymerization temperature is started. Unless

otherwise specified, the polymerization conditions are maintained for

three hours.

shing the residual monomer and cooling down the reactor.

recovered and dried overnight.

The polymerization is then stopped by simultaneously fla-

The polymer is

500 to 800 gram of polymer are obtained.

Evaluations. The melt flow index (MPI) under a 2.16 kilogram load

at 230 O C is measured according to ASTH D 1238.

content in the polypropylene is measured by X-Ray fluorescence.

ductivity of the catalyst is indirectly estimated on the basis of this

residual titanium. The bulk density (BD) of the polymer is measured

according to ASTM D 1895 (untapped). The isotactic index (11) is expres-

sed as the boiling heptane insoluble fraction of the whole polymer measu-

red according to ISO/DIS 1873. The tacticity index (TI) is the molar

fraction of isotactic triads in the polypropylene measured by l3C NMR

spectroscopy as indicated in l).

nal rigidity modulus measured at 100 O C according to ASTM D 1043.

molecular weight distribution (MWD) and the number (Mn) and weight (Hw)

mean molecular weights of the polymer are measured by steric exclusion

chromatography on a polymer solution of 1 gram per kilogram in 1.2.4 tri-

chlorobenzene at 135 O C .

catalyst is determined by computer microscopic picture analysis. The PSD

of the polymer is measured by successive siftings.

The residual titanium

The pro-

The stiffness G modulus (G) is a torsio-

The

The particle size distribution (PSD) of the

MORPHOLOGY

To evaluate the industrial suitability of a given catalyst, the

morphology of the produced polypropylene powder has to be considered.

This parameter is closely related to the economics of any type of indus-

trial process. An optimized size, shape and bulk density of the polymer

powder allows the highest polymer content and thus the highest reactor

throughput. A correct particle size distribution without fines or coarse

particles will simplify many industrial operations like centrifugation,

drying, fluidization or transportation of the powder.

morphology through the replication phenomenon are well known 2).

12 catalyst is in the shape of spherical particles having a very narrow

particle size distribution (fig. 1).

tribution can be estimated by the polydispersity index (PI) equal to the

weight (Dw) to number (Dn) mean diameter ratio:

The basic influence of the catalyst characteristics on the polymer

The SB

The width of the particle size dis-

Dn = Ci NiDi / Li Ni

PI = Dw / Dn

where Ni represents the number of particles of diameter Di.


a b

Figure 1. SEM micrograph of the typical morphology of the SB 12 catalyst. a) Magnification 2000 x. b) Magnification 500 x.

1000

800

600

400

200

10 20 30 SO 100 200 300 500 1000 2000

Particla stza (microns)

Figure 2. Typical particle size distribution of SB 12 catalyst

and polymer. Catalyst mean diameter: 25.9 micron. Polymer mean diameter: 557 micron

30. Nau solvay SB 12 TiC13 Polypropylene Gztnlyst 409

A perfectly undispersed distribution would.have a PI of 1.0.

catalyst exhibits a quasi perfect polydispersity index of 1.03 (table 1).

The SB 12

Table 1. Typical weight (Dw) and number (Dn) mean diameter and poly-

dispersity index of the SB 12 catalyst (diameters in micron)

The polymer powder replicates this morphology (fig. 2) giving a free

flowing easy to handle powder. Outstanding bulk densities up to 520 gram

per liter are regularly obtained.

For many plants with limitations on monomer or solvent recycling

capacity, the bulk density is the only way to increase the throughput of

the polymerization reactor. Higher bulk density powder means lower recy-

cled to polymer ratios and thus lower operating costs. To illustrate

this, a continuous bulk polymerization process using a catalyst giving a

polymer powder with a bulk density of BDo g/L is considered.

operates in liquid full conditions (no gas phase). The total throughput

of the reactor is THR kilogram per hour which splits into PP kg/h of poly-

propylene and (THR-PP) kg/h of propylene monomer to recycle, this last

number being the maximal recycling capacity of the unit.

residence time in the reactor, its mass content is as follows:

The reactor

If r is the

total mass content of the reactor : TJ3R.r

PP mass content of the reactor : PP.r

monomer mass content of the reactor : (THR-PP).r

Now suppose that another catalyst is used having the same properties

as the initial one, except that it gives a polymer powder with a bulk den-

sity BD lower than EDo.

the maximal apparent volume occupied by the polymer in the reactor is the

same with both catalysts, the polymer mass content of the reactor becomes

Let x be the ratio BD/BDo < 1. Supposing that


The reduction in polymer mass content leaves a free volume which will be

occupied by the monomer.

mass content given by

This leads to an increase AC3 of the monomer

where dc3 and dpp are the specific mass of monomer and polymer respecti-

vely. Since the monomer recycle capacity is limited, the reactor total

throughput must be reduced to a fraction

(THR-PP) / (THR-PP+AC3) [ 2 1

of its reference value. Taking in account the reduction of polymer con-

tent of the reactor (eq.l), the relative polymer reactor throughput in

percent of the initial throughput with the first catalyst is:

~OO.X.(THR-PP)/(THR-PP+AC~) 131

It is clear from equation [ 3 ] that the reduction in bulk density of

the polymer acts at two levels to reduce the polymer throughput of the

unit: through the factor x which represents the reduction in polymer con-

tent of the reactor and through the factor AC3 which accounts for the

higher recycled monomer to produced polymer ratio.

example of the dramatic effect of lowering the bulk density of the polymer

powder on the throughput of a model unit.

The figure 3 gives an

It is obvious from what preceeds that the very high bulk density

(equal to the one of pellets) and the extremely narrow particle size dis-

tribution of the polypropylene powder obtained from the SB 12 catalyst are

major advantages for the industrial practice.

MOLECULAR WEIGHT CONTROL

A catalytic system can only be used in a commercial process if a

broad range of different polypropylene grades can be produced.

most important parameters are those related to the molecular weight con-

trol: the average molecular weight and the molecular weight distribution.

In industrial practice, the melt flow index (HFI) of the polymer is gene-

rally used as a measure of the average molecular weight while the weight

to number average ratio (Hw/Mn) is often used to characterize the molecu-

lar weight distribution.

Among the

30. New Solway SB 12 TiCl, Polypropyiene Catahst 411

100

80

60

40

20

0 520 480 440 400 360 320 280 240 200

Bulk density of powder (g/C)

Figure 3. Effect of bulk density on the reactor throughput bulk process - 70 C - calculated according to eq. [ l ] to 131 with THR = 100 kg/h, PP = 55 kg/h, BOO = 520 g/L, dC-= 0.402 kg/L, dpp= 0.90 kg/L.

It is well known that average molecular weight is usually regulated

The dependance of the HPI by hydrogen in Ziegler-Natta polymerization 3 ) .

on the ratio of hydrogen to propylene in the gas phase of the polymeriza-

tion reactor at various temperatures is shown in figure 4. The data form

straight lines with an average siope of two, indicating that IF1 is a

function of the square of the hydrogen partial pressure.

easy computation of the required hydrogen concentration, and thus the

ready control of the mean molecular weight from fractional to very high

MFIs just by adjusting it.

Also noteworthy, is the fact that even at very low hydrogen partial

This allows an

pressure, the average molecular weight of the polymer is still governed by

it.

growing chain are negligible.

very high mean molecular weight polymer of fractional HPI under controlled

conditions which would be impossible in the presence of other significant

transfer processes.

It means that all other possible transfer mechanisms of the polymer

This allows the possibility to synthesize


100

0.5

0.2

Figure 4. Melt Flow Index of

polymer versus Hydrogen partial pressure in the gas phase of

the reactor - Bulk process - 3 hours - cocatalyst mDEAC

1

0.8

0.6

0.4

0.2

0

103 lo4 105 16 107 1 08

Molecular weig h t

Figure 5. Typical molecular weight distribution of the

polymer obtained with SB 12 catalyst - Bulk process - mDEAC cocatalyst

30. New Solvay SB 12 Ti& Polypropylene Cutalyst 413

Another interesting property of the SB 12 catalyst is its ability to

produce a polypropylene with a broad molecular weight distribution (HWD).

The Mw/Hn ratio of the polymer is typically higher than 8 over the whole

range of MFI. A broad MWD is

interesting since at a given HFI it allows easier processing of the resin

and higher crystallinity and stiffness of the final product.

difference between a broad and a narrow HWD polymer of same HFI lies in

the fact that the former contains a significantly higher amount of lower

molecular weight molecules. These are believed to be a lubricant for the

whole polymer in the melt and a autonucleating agent for the crystalliza-

tion process thus increasing both processability and crystallinity of the

resin.

MgC12/IB/TiC14/TEAL/EB catalyst (IB = internal Lewis base, TEAL =

triethylaluminium and EB = external Lewis base) are in the range 5 to 6

while this range is 8 to 9 with the SB 12 catalyst.

obtained starting with SB 12 polymer and depolymerizing it through

so-called controlled rheology techniques. Since the depolymerization is

proportional to the polymer chain length, the high molecular weight mole-

cules are more affected by the process than the lower ones.

a narrowing of the MUD. The extent of this effect can be controlled

through the depolymerization ratio (final HFI to initial HFI ratio).

A typical HWD curve is shown in figure 5 .

The main

For comparison, typical Mw/Hn ratios of polymers obtained with the

The narrower MWD required by some applications can also be readily

It results in

STEREOSPECIFICITY AND STIFFNESS

Besides the molecular weight, the most important parameter to control

for the production of commercial polypropylene is the stiffness of the

polymer. A modern catalyst system must be able to control the stiffness

of the product over a wide range independently of the other polymer pro-

perties.

intrinsic tacticity but this is not the only parameter.

the result of a combination of tacticity, crystallinity and HWD of the

resin. The effect of MUD has already been pointed out.

between tacticity, mean molecular weight and the stiffness of the polypro-

pylene produced with the SB 12 catalyst is illustrated hereafter.

The stiffness of the polypropylene is closely related to its

The stiffness is

The relationship

The only absolute method to measure the tacticity index (TI) of a

polymer is nuclear magnetic resonance.

measurement which depends on the tacticity of the polymer but also on

other parameters, mainly the mean molecular veight of the polymer.

is illustrated in figure 6 and 7.

All other methods give an indirect

This


- C 0

0 .- c e c

I 0 - E v

a 0 0 .- L c

0

0

0

.- c

c

.- E E

1

0.99

0.98

0.97

0.96

0.95

0.94

0.93

0.92

Melt Flow Index (g/lOrnin)

Figure 6. NMR tacticity index as a function of the mean molecular weight of the polymer - bulk homopolymerization process - 3 hours - cocatalyst mDEAC

h

v E L 0

- E 0

0

a

n - - 0 n C

0 C

- c a I

100

99

98

97

96

95

94

93

92

91

90 . 0.25 0.5 1 2 4 8 16 32 64

Melt Flow Index (g/lOrnln)

Figure 7. Conventional isotactic index as function of the mean molecular weight of the polymer - bulk homopolymerization process - 3 hours - cocatalyst mDEAC

30. New Solwy SB 12 TiC13 Polypropylene Catalyst 415

The intrinsic stereospecificity of the SB 12 catalyst measured by the NHR

TI is independent of the mean molecular weight but is closely related to

the polymerization temperature (figure 6). This is understandable if the

activity of hydrogen is limited to the termination of the polymer chain

growth and is thus restricted to the ends of the polypropylene chain which

have no influence on the global tacticity. The conventional and widely

used isotactic index (11) measured by the boiling heptane insoluble frac-

tion of the polymer depends on the mean molecular weight (figure 7).

given tacticity, low molecular weight molecules are more soluble than

heavier ones such that the amount of soluble polymer increases with the

HFI. The conventional I1 is thus not a truly accurate measure of the

tacticity of the polymer and can only give an approximation of it.

At

The stiffness of the polymer measured by the torsional G modulus is

also strongly dependent on the mean molecular weight of the polymer as

illustrated in figure 8.

reorganize itself themselves during the crystallization process so that

high UFI polymers achieve a higher degree of crystallinity and stiffness.

Lower molecular weight molecules can more easily

Melt Flow Index (g/lOmin)

Figure 8. Stiffness G modulus as a function of mean molecular weight of polymer - bulk homopolymerization process - 3 hours - cocatalyst mDEAC


To correlate the stiffness of the polymer to its tacticity, a correction

mechanism for the G modulus has to be introduced. Although the dependence

of the G modulus on the logarithm of the HFI is not truly linear, it is a

reasonable approximation if restricted to a limited range of HFI. The

result of a linear semi-logarithmic regression is given in table 2 and

illustrated in figure 9. Except for the polymerization tests carried out

at 50 O C , where the HFI range is probably too narrow, the linear plots are

reasonably parallel indicating that the influence of the molecular weight

on the polymer stiffness is independent of the polymerization temperature.

Table 2.

tures. Semi-logarithmic regression as a function of the melt flow index - bulk homopolymerization process - 3 hours - cocatalyst lnDEAC Units: G modulus in daN/cm2; IF1 in g/lOmin.

Stiffness G modulus of polymer obtained at various tempera-

50 O C 60 O C 70 O C 75 o c 80 OC

HFI G HPI G HFI G HFI G HFI G

1.4 710 0.4 586 0.9 620 1.2 563 1.6 520

1.7 710 4.0 742 5.1 701 5.9 654 5.8 616

3.1 785 4.3 770 6.3 701 6.0 651 10.7 636

3.4 825 11.0 768 10.7 724 20.8 709 29.6 718

23.4 822 19.3 738 22.0 706

48.5 867

Lesults of the regression: G = a + b.log(HF1) 65: G modulus at HFI = 5

a = 656.1 a = 653.5 a = 629.3 a = 558.8 a = 490.1

b = 289.5 b = 128.4 b = 88.0 b = 113.9 b = 152.6

r2 = 0.928 r2 - 0.955 r2 = 0.971 r2 = 0.991 r2 = 0.988

G5 = 858.6 G5 = 743.3 G5 = 690.8 G5 P 638.5 65 P 596.8

900

800

700

600

500

0.1 0.2 0.5 1 2 5 10 20 50 100

Melt Flow Index (g/lOrnin)

Figure 9. Semi-logarithmic regression plot of the stiffness G modulus as a function of the melt flow index - data from table 2 - bulk process - 3 hours - cccatalyst mDEAC

n c 0

U

.- c

e .I-

L O - ; v

n -a 0 .- L c

U

U

0 n

.- e

c

.- E E

1

0.99

0.98

0.97

0.96

0.95

0.94

0.93

0.92 45 50 55 60 65 70 75 80 85

Polymerization temperature ( C)

Figure 10. NMR tacticity index as a function of polymerization temperature bulk homopolymerization process - cocatalyst mDEAC


By using the relation given in table 2, the stiffness modulus at a

reference HFI can be calculated.

chosen as a reference and the calculated value of the stiffness modulus at

this HFI is called G5. The dependence of this normalized G modulus and of

the NHR tacticity index on the polymerization temperature can now be cal-

culated.

This means that the normalized stiffness and the intrinsic tacticity of

the polypropylene are linearly correlated as shown in figure 12.

words, the stiffness of the produced polypropylene is proportional to the

intrinsic tacticity of the polymer provided the stiffness modulus has been

corrected to take into account the effect of the mean molecular weight of

the polymer.

The medium range HFI of 5 g/lOmin is

Both are linear as shown in table 3 and in figure 10 and 11.

In other

Table 3.

function of polymerization temperature - bulk homopolymerization process cocatalyst DlDEAC - Units: molar fraction for TI; daN/cm2 for 65

NHR tacticity index and normalized stiffness modulus as a

Polym. temp. 50 O C 55 O C 60 O C 70 O C 75 O C 80 O C

NXR TI 0.971 0.963 0.967 0.954 0.954 0.947

G5 858.6 - 743.3 690.8 638.5 596.8

Results of linear regressions of the form Y I a + b.T (T in "C)

a b r2

NMR TI

G5

1.007 -0.73 10-3 0.908

1267. -8.38 0.984

From this discussion, it is obvious that both the tacticity and the

stiffness of the polypropylene produced with the SB 12 catalyst can be

varied in a broad range, independent of the HPI of the polymer, simply by

adjusting the polymerization temperature. The SB 12 catalyst achieves an

exceptionaly high stereospecificity level allowing the production of very

high stiffness polypropylene in the most up-to-date simplified processes

without an atactic by-product removal section.

30. New Solvay SB 12 TiC13 Poiypmpylene Cukzlyst 419

n FI E

Polymerization temperature ( C)

Figure 11. Reference G modulus at Mf l = 5 g/lOmin as a function of polymerization temperature - bulk homopolymerization process - mDEAC cocatalyst

n 3 3 0

-

E

1000

900

800

700

600

500 0.93 0.95 0.97 0.99

rnm isotactic triads (molar fraction)

Figure 12. Relation between the reference G5 stiffness modulus and the NMR tacticity index - bulk homopolymerization process - cocatalyst mDEAC


It is actually possible to modulate the tacticity of the polymer from the

medium crystallinity range characteristic of most commercial product (TI =

0.93 to 0.95) to the high crystallinity range (TI above 0.96). This gives

access to an exceptional broad range of polymer stiffnesses.

PRODUCTIVITY

To avoid the costly catalyst residue cleanup step existing in the

conventional PP processes, a catalyst with a productivbty of at least

8,000 kilogram of polypropylene per kilogram of TIC13 is required.

performance is unachievable with a first generation TIC13 and is hardly

reachable with the second generation but is readily attainable with the SB

12 catalyst as illustrated in figure 13.

ductivity levels which are unique for titanium trichloride catalysts and

which lie in the range of most supported type catalysts: productivities of

over 15,000 kilogram per kilogram of catalyst are easily obtained.

allovs SB 12 to be used in the most up-to-date simplified process with no

catalyst removal section.

This

The SB 12 catalyst reaches pro-

This

The productivity of the SB 12 catalyst depends on polymerization con-

ditions, mainly the monomer concentration and the polymerization tempera-

ture. The dependence on monomer concentration is of first order allowing

an easy computation of the productivity level attainable in each kind of

process. Like stereospecificity, the productivity of the SB 12 catalyst

is closely related to the polymerization temperature. It can be used over

a broad range of temperatures, typically from 50 to 80 O C , with a broad

modulation of the productivity level. In this temperature range, the

activity of the catalyst can be adequately represented by an Arrhenius

semi-logarithmic relation as expressed in table 4. In our laboratory con-

ditions, the catalyst activity activation energy is found to be

33.2 kilojoule per mole of TIC13 with a squared correlation coefficient r2

of 0.980.

Figure '13. Productivity as a function of the melt flow index at various polymerization temperature - bulk homopolymerization process - 3 hours cocatalyst mDEAC

n n 0 I-

2 0

a 0) Y v

z .- c U

U 2 a

28

24

20

16

12

8

4

0 0 2 4 6

Polymerization time (hours)

Figure 14. Productivity as a function of the polymerization time - bulk homopolymerization process - 70 C - cocatolyst mDEAC


Table 4.

activity and polymerization temperature.

to be 33.2 kJ/mol of Tic13 with r2 - 0.980 - bulk homopolymerization process - 3 hours - cocatalyst mDEAC - HPI = 2 g/lOmin.

Arrhenius semi-logarithmic relationship between catalyst

The activation energy is found

Temperature 1/RT Catalyst activity

(OC) (OK) (mol/kJ) (gPP/h.gTiCU)

Exptl. Calctd.

50 323 0.372 2275 2392

55 328 0.366 2835 2919

60 333 0.361 3800 3446

70 343 0.350 5150 4966

75 348 0.345 5875 5862

80 353 0.341 6325 6695

The productivity is also sensitive to the hydrogen partial pressure

but to a lower extent. The presence of hydrogen positively affects the

catalyst productivity as already mentioned in the literature with diffe-

rent kinds of TiC13/AlEt2X (X - halogen) catalytic system 4). remains limited and is restricted to the low IF1 range (low hydrogen con-

centration in the polymerization medium).

This effect

Another interesting feature of the SB 12 catalyst is its low deacti-

vation rate (figure 14). This results in a nearly constant reaction rate

allowing easy polymerization control and production of block copolymer by

multiple step polymerization.

CONCLUSION

In this paper, a review of the manifold stringent requirements of a

modern commercial polypropylene production catalyst is discussed.

research and development devoted to the TIC13 catalyst has resulted in the

third generation SB 12 catalyst, a product combining a unique set of the

most desirable properties.

simplifications and the optimization of the polymerization reactor

throughput and productivity.

The

Process economics are favoured by technical

30. Nau Solvay SB 12 TiC13 PoryproPrlene catalyst 423

The accessible product range is also broadened thanks to the exceptional

intrinsic stereospecificity and molecular weight control of the catalytic

system.

trol of the polymerization conditions due to the catalyst properties.

addition, future progress can be foreseen as a result of specialized

development studies of this type of titanium trichloride catalyst curren-

tly under way.

nigh quality and consistency are favoured by easy and smooth con-

In

REFERENCES

1. J.C.RANDALL, "Polymer Sequence Determination. Carbon 13 NMR method",

Academic Press, 1977, chap. 1 and 2

2. J.BOOR, "Ziegler Natta Catalysts and Polymerization", New York,

Academic Press, 1979, chap. 8.

G.NATTA, G.HANZATT1, P.LONG1, F. BERNARDINI, Chem. Eng., Milan, 41, 519, (1958)

3.

4. J.BOOR, "Ziegler Natta Catalysts and Polymerization", New Yark,

Academic Press, 1979, chap. 10.


425

3 1. Polymerization of Cyclic Olefins with Homogeneous Catalysts

W. Kaminsky, A. Bark and I. Dtlke I n s t i t u t fiir Anorganische und Angewandte Chemie, Universittlt Hamburg, Martin-Luther-King Platz 6 ,

2 Hamburg 13, F. R. G.

Cyclic olefins like cyclobutene, cyclopentene, and norbornene can

be polymerized to give isotactic polymers with chiral metallo-

cene/aluminoxane catalysts, especially with et(bisindeny1)zir-

coniumdichloride/methylalumoxane.

The polycycloalkenes show extremely high melting points which are

395OC for polycyclopentene, 485OC for polycyclobutene and over

6OOOC for polynorbornene, which is more than the decomposition

temperature.

13C-NMR spectroscopy provides information about the structure of

the highly crystalline homopolymers. To lower the melting points,

copolymerization with ethene or propene is carried out. The copolymerization parameter rl of the olefins ethene/cyclopentene increases with temperatures from 80 (-10°C) to 300 ( Z O O C ) . Even

when in solution the copolymers obtained using one enantiomer of

the chiral zirconocene show a small optical rotation. Polymers of

rigid cycloalkenes like dimethanooctahydronaphthalene with ethyl-

ene are amorphous and feature high Tg values. They could be used

as starting materials for optical discs. The information about

aging reactions between zirconocene and aluminoxane sheds more

light on the mechanism of homogeneous olefin catalysts.

Ziegler-Natta catalysts based on chiral metallocenes in combina-

tion with aluminoxane allow the synthesis of ieotactic polyole-

f ins1 f

zirconiumdichloride catalyst as well as the ethylene(bi8tetra-

. A high activity is given with the ethylene( bisindenyl) -

426 W. Karninsky. A. Bark and I. Dake

hydroindenyl)/methylaluminoxane system in solvents like toluene or

heptane3). Moreover this catalyst was succesefully employed in the

homopolymerization of cyclopentene and copolymerizations of cycloalkenes with ethylenel 1 . The homopolycyclopentene is highly crystalline and insoluble in common hydrocarbons, The cyclic mono-

mers polymerize without any ring-opening. In principle, there are

four different isomeric structures (Fig. 1) by the reaction of the double bond.

trans

double di-syndiotactic

cis di-isotactic

di-syndiotactic

Fiq. 1 Kinds of Structures for Polycyclopentene

The opening of the double bond could take place in a cis or a

trans fashion thus forming two erythro or thero isomers. The

threo-di-syndiotactic form is expected to show optical activity6). Sequence analyses of the copolmere were carried out by 13C-NMR-

measurements. Signals which would indicate ring-opening could not

be detected. In spectra of polymers with 28 mol-% cyclopentene and

72 mol-% ethene units minor amounts of short cyclopentene blocks can be recognized. This indicates that a very good random

distribution is given. Cyclopentene ethene copolymers show a

31. PolymeriUrtim of Cyclk Olefins with Homogeneous Cahlyst 427

broader molecular weight distribution than homopolyethyl-ene.

&/bf,, values are ranging from 3 to 4,s.

The structure of homopolycyclopentene especially the inter-

pretation of the solid state 13C-NMR spectrum could be clearified

recently. More information can be gained by investigation of the

polymerization and copolymerization of other cyclic olefins.

HOMOPOLYMERIZATION OF CYCLIC W(ENES

Cyclic alkenes as cyclobutene, cyclopentene, and norbornene could

be polymerized with the zirconocene/methylaluminoxane catalyst.

Table 1 compares the activities and the melting points. The

TABLE 1: Homopolymerization of Cycloalkenes with Et(Ind)2ZrClZ/

MA0 in Toluene

Monomer Temp. Activity Melting Point

(OC) kg Polymer in Vacuum

Cyclopentene 22 195 395

Cyclobutene 0 149 485

-10 50 485

Norbornene 20 40 >600

0 32 395

activities for the polymerization of cyclobutene and cyclopentene

are high, whereas the activity of norbornene is significantly

lower. The conversion of the polymerization of cyclopentene and cyclobutene vs.time is plotted in Fig. 2. Following a rapid start

the rate decreases to become linear after a few hours for a long

period.

428 W. Kaminsky, A. Bark and I. Diilse

I Yield (X) 22 Oc

50

GO .

-10 OC

fh/ 10 15 20 1 2 3 6 5

Fig. 2 Conversion of the Polymerization of Cyclopentene and

Cyclobutene vs. Time at Various Temperatures

At the same temperature, the activity for the polymerization of

cyclobutene is about five times that of cyclopentene. The melting

points are eurprisingly high. Under vacuum (to have avoid oxi-

dation), they were found to be 485OC for polycyclobutene, 395OC

for polycyclopentene, and over 6OOOC for polynorbornene. The de-

composition temperature lies in the same range. The melting points

were measured by means of DSC, in an evacuated tube as well as

with temperature dependent wide angle X-ray diffraction measure-

ments using syncroton radiation (Fig. 3) which was also carried

out under vacuum. Every 20 s a spectrum was taken. The temperature

was varied by a program (compare the ordinate of the figure).

31. Polymeniathi of Cyclic Olefins with Homogenems Gatolyst 429

tlsec I

1000

I

700 3550 'A1

FiQ. 3 X-ray Plots Using Syncrotron Radiation of Polycyclopentene

t = 100-650 8ec.t Heating from 2OOOC to 395OC; t =

650-1000 sec.: Cooling from 395OC to 5OoC

The intensity I was measured as a function of temperature and diffraction angle 28. The plots show a decrease in intensity with

increasing temperature for all signals. At 395OC they disappear, which means that the polymer becomes completely amorphous. After

cooling the sample, the signals appear again with even higher in-

tensities. Therefore, a higher degree of order is achieved by tempering. Table 2 shows the polymerization results of cyclopentene with various zirconocenee.

430 W. Kaminsky, A. Bark and I. Dike

TABLE 2 Polymerization of Cyclopentene (100 ml) with Zirconocen

( mol) I Methylalumoxane (200 mg)

................................................................. Zirconocen Temp. Time Yield

Cp2 ZrC12 3OoC 20 h - Et(1nd)~ZrCl~ l0OC 90 h 13,6 g

Et(1nd)~ZrCl~ 25OC 72 h 2OIO g Et(1nd H4)2ZrC12 22oc 10 h 2415 g

There ie no activity when Cp2ZrC12 is used. Only the chiral cata-

lyst is able to polymerize cyclopentene. The eame reeult ie found

for the other cyclic alkenes.

Since the homopolymers of cyclic alkenes are insoluble in hydro-

carbons, it is difficult to study their etructure. A poasible way

for theee studiee was found by lowering the molecular weight to

get oligomers which are soluble in hydrocarbons. This can be

achieved by changing the polymerization conditions. Higher tem-

peratures, higher zirconocene concentration and lower monomer con-

centration lead to oligomere. Fig. 4 compares the 13C-NMR spectrum

of soluble oligomeric polycyclopentene with the solid state spec-

trum of ineoluble polycyclopentene. All peake could be identified.

31. Po1,meriZariOn of Cyclic Ohfins with Hmgeneuw Gakzlyst 431

OL IGOCYCLOP EN TEN E C 13 -ART. - NMR

I H

-CH I ...............

I n

. .

I ...... I .*. * . . . . .

. . . . * . . . -c- . . c= * .* .

H .* .. . . H *. . . . ... . . n - . . . .

POLYCYCLOPENTENE Cl3-S -NMR

. - . . . . . . . . . . . . . .

. . * .

00- . . . _ 0-

. .,

c

J I

3

L I , . , . I 1 -

180 140 100 60 20 -20 ppm

Fiq. 4 13C-NMR Spectrum (75 MHz) of Oligocyclopentene (in Solution) and Polycyclopentene (Solid State)

There are two different kinds of end groups:

Even under these conditions, no ring opening reaction occurs. The

average molecular weight of the oligomere measured cryoscopically

in camphene is ?sg which means that 10-12 cyclopentene units are

linked. The melting point of the homopolycyclobutene is higher

than that of the polycyclopentene. It is a crystalline polymer

(see Fig. 5). The X-ray spectrum shows only two signals; the so l id state 13C-NMR spectrum is simplified, too (see Fig. 6).

432 W. Kaminsky, A. Bark and I. D&e

10 16 22 28

Fiq. 5 X-ray Spectrum of Polycyclobutene Powder

I - - -

140 120 100 80 60 GO 20 0 PPm

Fiq. 6 Solid State 13C-NMR spectrum (75 MHz) of Polycyclobutene

The two peaks at 6 - 27 and 40 ppm result from the CH2- and the CH-group of the four membered rings.

31. Polymerization of Cyclic Olefins with H~genew Gztalyst 433

The processing of homopolynorbornene would be extremely difficult

due to the high melting point. On the other hand copolymers of ethylene with integrated rigid monomer units of this kind would be

of considerable interest for optical polymers. Polymerization

conditions and yields with two different catalysts Cp2ZRC12/MAO

and Et/Ind)aZrC12 are listed in Table 3.

TABLE 3 Copolymers of Norbornene (1,4 g) and Ethylene (1 bar)

with Zirconocene and Methylaluminoxane (480-600 mg) in

100 ml Toluene

Zirconocene (moll Temp. Time Yield

Et(Ind)2ZrC12 1,6*10'7 25OC 0,5 h lI9 g

Cp2ZrCl2 1 I 7 loe7 25OC 0,9 h 0123 g

Et (Ind) 2ZrCl2 1 I 6 6OoC 0,s h 218 9

Cp2ZrCl2 1 I 7 6OoC 0,s h 213 g ..................................................................

From Table 3 it is obvious that the activity of the chiral cata-

lyst is much higher (by a factor of 10 at 25OC, by a factor of 100

at 6OOC) than that of the simple biscyclopentadienylzirconium com-

pound. Moreover under comparable conditions, the incorporation of

the cyclic olefin is improved with the chiral catalyst. The same

was previously found for the polymerization of other a-olefins.

Again we found a random distribution of the norbornene units in

the polymer chain using 13C-NMR measurements. . Dimethanooctahydronaphthalene (DMON) is more rigid than

norbornene. The copolymerization product of DMON with ethene is

amorphous featuring a high Tg value. It is possible to incorporate

12 mol-% and more of DMON (Table 4).

434 W. Kaminsky, A. Bark and I. Dike

TABLE 4 Copolymers of Dimethanonaphthalene (DMON) and Ethene Catalyzed by Metallocene ( 10'6m01) /MA0 (420 mg) in

Toluene (100 ml)

DMON Ethene Metallocene Temp. Time Yield Incorp.

(ml) (bar 1 (mol) (OCI (h) ts) (mol-%

5 3 Et ( Ind) 2ZrC12 25 0 , 3 7,7 - 10 3 Cp2ZrCl2 25 0,8 0,9 - 10 1,s Et(1nd)~HfCl~ 10 3 O t 3 - 3 1 Et(Ind)2ZrC12 25 0,5 4,l 12,5

3 1 Cp2ZrC12 25 0,5 0,2 2

Various aluminoxane containing catalysts are used. Again, the

Et(Ind)2ZrC12/MAO system ie best. The transition metal concen-

tration is in the region of lom5 mol/l.

31. PolymeriUrtion of Cyclic Olefiins with H o n r o ~ Catalyst 435

k-

FIG. 7 13C-NMR Spectrum (75 MHz) of the Ethene/Dimethano-

naphthaline (7 mol-8)

436 W. Kaminsky, A. Bark and I. DBke

Fig. 7 shows the 13C-NMR spectrum of the ethene-DMON copolymer

with a content of 7 mol-% DMON units. The copolymer is amorphous

at room temperature, it is insoluble in hydrocarbons, and has an

excellent transparency, thermal stability, and chemical resi-

stance. These properties make the copolymer useful for optical

discs.

Copolymers of cyclopentene (Cyp) with alkyltrimethylsilane (Mi) were synthesized in addition to the ones of cyclopentene with

ethene7) that were described previously. It could be assumed that

the bilky silyl side groups in combination with the cyclopenten

unit would promote optical rotation. The S enantiomeric form of Et(IndH4)2ZrC12 was used as an optically active catalyst. Table 5

shows the polymerization conditions.

TABLE 5 Copolymerization of Cyclopentene and Allyltrimethylsilane

with S-Et(IndH4)2ZrCl2/MkO (800 mg/l) in Toluene

.................................................................. Po1ym.-Temp. Zr-Comp. cyp : A s i Time Activity

("C) ( mol / 1 ) (mol / 1 ) (h) ( kq COPO 1 mol Zr-CM-h

28 1,2 -10-4 3,7 :o, 12 48 012

19 1,g -10-4 6,l: O,86 92 0,Ol 20 0,56 3,5:0,19 45 3,1

17 0,56 5,6 :0,01 40 0,07

16 1,5 .10-4 5,6 :O, 01 48 0,07

15 0,95 2,2:0,12 90 0,02

The activity of the copolymerization decreases drastically in the

first 10 minutes by the factor of 20 to become nearly constant

after 30 minutes.

The copolymers were characterized by lH-NMR, 13C-NMR or IR-spec-

troscopy (Tab. 6). The optical activity was measured in solution

at several wave lengths (solvent: decahydronaphthalene).

31. PolyunmiUrtion of Cyclic Okfiws with Honzogeneacs Cutalyst 437

TABLE 6 Physical Properties and Optically Activity of Cyclopen-

tene/Allyltrimethylsilan Copolymers

20 POlym. M, Melting Reaction Polymer [a] 365

Temp. Point Mixture Composition (drq m2

("C) ("C) cyp:Asi CyprASi ' dag)

28 14 000 200 31:1 1111 - 4,4

20 700 180 18:l 7:1

19 8 400 7:l 2:l - 8,O

17 8 500 560:l 28:l - 1716 16 9 500 56011 25:1 - 7,5

mol fatio mol ratio

As expected, melting points are relatively high with 200-180°C for

those polymers. All samples ahow an optical activity between -4

and -17,6O. There are two explanations for the opticaly activity.

The relatively low molecular weight could indicate the in-fluence

of different end groups on chiral cyclopentene or allyl-trimethyl-

ailan units inserted in the same stereospecific manner. The op-

tical activity may also result from the cyclopentene units only.

They would then have to be inserted in the di-eyndiotactic

fashion. It is clear that the rotation does not result from an

excess of one of the enantiomeric helix structures. In this case

the value would have to much higher.

*

We thank BMFT and Hoechst AG very much for sponsoring this re-

search.

438 W. Kaminsky, A. Bark and I. Dake

LITERATURE

1. J.A. men, J.Am.Chem.Soc., 106 (1984), 6355 2 . W. Kaminsky, K. KQlper, H.H. Brintzinger, F.R.W.P. Wild,

Angew.Chem. 97 (1985), 503; Angew.Chem.Int.Ed.Eng1. 24 (1985) 507

3. W. Kaminsky, Angew.Makromol.Chem. 145/146 (1986) 149

4. W. Kaminsky, A. Bark, R. Spiehl, N. M6ller-Lindenhof, S. Nie-

doh, in: Proceedings, Intern. Symposium on Transition Metals and Organometallics as Catalysts for Olefin Polymerization, ed.

by W. Kaminsky, H. Sinn, Springer Press, Berlin 1988, p. 291

5. W. Kaminsky, R. Spiehl, Makromol.Chem. 190 (1989) 515 6. G. Natta, Pure a.Appl.Chem. 12 (1966) 165 7. S. Niedoba, Dissertation, University of Hamburg 1989

439

32. Syndiospecific Propylene Polymerizations with iPr [CpFlu] ZrClz

JOHN A.EWEN, M.J.ELDER, R.L.JONES, S.CURTIS AND H.N.CHENG+

Fina Oil and Chemical Company, Box 1200, Deer Park, Texas 77536

Research Center, Hercules Incorporated, Wilmington, Delaware 19894 +

ABSTRACT

Syndiotactic polypropylene (sPP) with a ... rrrrrmrrrrrmmrrrcr... mixed microstructure is obtained with the iPr[CpFlu]ZrC12/MA0 (MA0 - methylaluminoxane; Cp - cyclopentadienyl anion; Flu - fluoreny'l anion). The structures of the metallocene and the polymers are in

accord with chain migratory insertion being the predominant mechanism

of chain growth and with stereochemical control being provided by the

alternating handedness of polymerization active, cationic Zr

monoalkyls.

INTRODUCTION

Historically, cationic transition metal alkyls have been

suspected to be the active species in many types of homogeneous olefin

polymerizations for almost three decades. The ion pair model was

inferred from a number of different observations, such as solvent

effects, electrochemical measurements, theoretical calculations, model

ionization reactions, in situ syntheses of alkylated cations, the study o f well-defined aluminum-free catalysts which are stable ionic

salts,') and from the stereochemistry of olefin polymerizations. In this contribution we present the crystal structure of

iPr[CpPl~]zr( C H ~ ) ~ , bulk and slurry propylene polymerization results

with MA0 as a cocatalyst, polymer C-13 NMR data, and kinetic or statistical models that relate the sPP polymer microstructures to the

structure of the metallocene and generally accepted mechanisms of

stereochemical control and polymerization.

microstructure are consistent with stereoselective copolymerization

2 )

The meso triad defects in the ... rrrrrmmrrrcc...rrrrrmrrrrr...

440 J. A. Ewen, M. J. Elder, R. L. Jones, S. Curtis and H. N. Cheng

schemes in which chiral iPr[CpPlu)Zr-R+/MAO- active sites control the

stereochemistry by an enantiomorphic site control mechanism. The

racemic placements are accounted for with chain migratory insertions

resulting in systematic site isomerizations. The fraction of isolated

meso dyads are in accord with coordinatively unsaturated Zr

intermediates isomerizing independently of propylene addition and with

slow net monomer insertions.

EXPERIMENTAL

Polymerizations. The metallocene derivatives and cocatalyst

were precontacted for 20 minutes in toluene solutions containing 10.7

wt-% of Schering's HA0 with MW = 1,300. In bulk polymerizations, the

catalyst solution and liquid propylene were added sequentially to a

magnedrive, packless Zipperclave at room temperature and

prepolymerized on heating the reactor contents, with stirring, to the

reaction temperature within 3 minutes of monomer addition.

sequentially in pentane slurry polymerizations, warmed, and held for 5 minutes at 65OC; followed by rapid addition of sufficient liquid

propylene to obtain the targeted pressure.

Polymer C-13 NMR. Syndiotactic polypropylene samples were

routinely purified before C-13 NMR analyses with triple

recrystallizations from 1 wt-%, hot xylene solutions by cooling to

OOC. The polymers were filtered, washed with pentane, and dried under

vacuum after each crystallization.

polymers obtained with the MA0 systems were dissolved as 20% (w/w)

solution in 1,2,4-trichlorobenzene/d6-benzene and run on a Nicolet

NT360 WB spectrometer. The experimental conditions were: Transmitter

frequency, 90.5559 MHz; decoupler frequency, 360.1233 MHz; pulse

repetition time, 4 sec; acquisition time, 1.38 sec; pulse angle, 70

degrees; memory size, 16K points; spectral window, 6024 HZ with

quadrature detection. The probe temperature was set at 100DC.

PP samples was accomplished with the computer program CALMOD; based on

C-13 NMR shift rules for methyl substituted alkanes and

polymers.

500 cc of pentane and the metallocene/MAO solutions were added

The sample of sPP used for chain end analysis and the isotactic

The tedious task of assigning the numerous small resonances in

3,4)

32. Syndwtactic protrUlene PolynreriUrtMn with iPr[CpFlu]ZrCI, 441

All other sPP and the catalyst samples were recorded with a

Varian VXR-5000 spectrometer. The polymers were 5-10% (w/w) solutions

in TCB with d6-benzene added as a lock solvent. C-13 NMR spectra were

obtained at 15.43 MHz and 12OOC using 90Opulse width and a 15 second

delay time. Inverse gated decoupling with Waltz modulation was used

to suppress NOE's for purposes of quantitation. The LAB ONE curve

fitting program from New Methods Research Inc. (NMRi) in New York was

used to quantify the SPP r r centered methyl pentads and hexads in the

SPP spectra.

Metallocene and Ligand H-1 NMR. H-1 NMR samples were 10-20 mg

in 1 ml CD2C12 and measured at 299.95 MHz at the ambient probe

temperature. 90° pulse width was used with 3.74 seconds acquisition

time and 20 second delay. All chemical shifts ace reported relative

to TMS - 0.00 ppm. single, dilute decahydronapthalene solutions (ca. 0 . 0 5 g/dl) with a

Viskotek Corp. (Houston) model 100 Differential Viscometer calibrated

with NBS 1475 linear polyethylene ( h - 1.18 dl g-').

Data acquisition was executed with an IBM-XT computer using

Viskotek's IV-1 software package. The viscosity average molecular

weights were calculated by substitution into the Mark-Houwink equation

for polypropylene suggested by Kinsinger and Hughes

Intrinsic Viscosity. Intrinsic viscosities were determined from

5)

Dec 0.80 - 1.10 x M~

with the approximation that Mv - Mw being regarded as reasonable since their standards had MJMn - 1.2 to 1.3.

DSC Analyses. Calorimetric measurements were made with a

Perkin-Elmer model DSC-7 instrument model DSC-7 instrument calibrated

at 10°K/min against indium (429.78OK). The heat of fusion of indium

(6.80 cal/g; 28.45 J/g) was used as a calorimetric calibration.

Polymer samples (ca. 5 mg) were encapsulated in standard aluminum

pans. DSC examinations were performed with heating and cooling rates

of 10°K/min on "as-polymerized" samples and on samples previously

heated to 45OoK, held at this temperature for 5 minutes, and cooled at

10°K/min with baseline correction. The higher of the two melting

points on the second melt are reported. DSC melting temperatures,


crystallization temperatures, heats of crys.tallization, and heats of

fusion were calculated with the Perkin-Elmer TADS-7 program.

using a Vacuum Atmospheres glovebox or Schlenk techniques. Toluene,

pentane and tetrahydrofuran solvents were distilled under nitrogen

from purple sodium/benzophenone-ketyl. Dichloromethane was distilled

from fresh calcium hydride under nitrogen. Published procedures were

used to synthesize and purify the metallocenes.

Synthetic Procedures were performed under an inert atmosphere

2b16)

RESULTS

molecular Structure of i P r [ C p F l ~ ] 2 r ( C H ~ 1 ~ The molecular

etructure of this zirconium derivative is considered in some detail because it is the geometrical arrangement of the iPrCpFlu ligand that is ultimately responsible for the syndiospecific polymerizations described in later sections. In addition, the zr-ligand bonding mechanisms are of considerable theoretical interest.

X-ray diffraction has confirmed that ~ P ~ ( C ~ F ~ U ] Z ~ ( C H ~ ) ~ is

isostructural with the Hf dichloro analog.2b) The atom numbering

scheme, structure, and zirconium bond lengths and bond angles are

summarized in Figure 1. The atoms are represented by their 50% probability ellipsoids. The centroid (CEN) distances (angstroms) and

angles (degrees) are Zr-CEN(F1u) 2.28; Zr-CEN(Cp) 2.19; CEN(F1u)-Zr-

CEN(Cp) 117.9 . The prochiral dimethyl complex has bilateral symmetry. The Cp

and Flu C5 ring carbon atoms that face each other on opposite sides of

the molecule are mirror images of each other. The syndiotactic

specific catalyst precursor is therefore a "syndiotactic" complex. Flu-Zr bonding mechanism. The differing Zr-C bond distances

listed with Figure 1 result from the mechanisms of bonding and from

intramolecular nonbonded steric contacts. The mean n Cp-Zr distance

and the o Zr-CH3 distance are in the normal range for zirconocenes. The more interesting Zr-C distances for the C5 fluorenyl ring

are 2.46(1), 2.55(1) and 2.69(1) angstroms for C(l), C(2) and C(3)

respectively. Analogous progressive increases in the N-C bond lengths on progressing from the Flu bridgehead carbon atom to the C5 ring

substituents distal to the bridge were given earlier as evidence for a

controversial n3 Hf-Flu bonding mechanism.

7)

5

2b)

32. SvndwrcrctiC prolrvlene PolymetiaatMn with iPr[CpFlu]ZrClz 443

c1

c1

Bond Distances

C(23) - Zr 2.26

C(22) - Zr - C(23) = 98.3"

Figure 1. Molecular structure for i P r [ C p F 1 ~ ] 2 r ( C H ~ ) ~

444 J. A. Ewen. M. J. Elder, R. L. Jones, S. Curtis and H. N. Cheng

n-donation from Flu to zr is on firm grounds since the crystal structures reveal a nearly planar arrangement of C(1) with respect to

C(2), C(5) and C(14). monohapto a-donation mechanism.

controversial h3 attachment. that steric and electronic contributions to the differing Zr-Flu bond lengths cannot be distinguished form the crystal structure alone. 8 )

Precedent for nonbonded CH3-C1 contacts forcing a distal C5 ring

carbon of a formally h , air-stable indenyl ligand 2.63 angstroms away

Similarly, Cl(l)-C(9) and C1(2)-C(13) are within contact distance in

iPr[CpFlu]ZrC12.

obtained with iPr[CpFlu]ZcC12 relative to bridged indenyl and

cyclopentadienyl complexes is consistent with Flu being a remarkably better n-donor than either Ind or Cp. On the other hand, chemical

evidence supporting n3 fluorene bonding comes only from trivial protonation reactions occurring preferentially at C(1) over C(17).

Bonding descriptions intermediate to h3 or h5 resonance structures for all of these distorted metallocenes would be intuitively more

satisfying.

membered Zr-C(1)-C(14)-C(17) chelate ring is appreciably strained. Crystallographic evidence for this is discussed with the aid of two

perspectives of the molecular structures for i P r [ C p F l ~ ] H f C l ~ ~ ) and

Et[ Ind]2HfC126a) depicted in Figure 2 .

unbridged hafnocene derivatives. In contrast, the structure of

iPr[CpFlu]HfC12 is similar to the strained, methylene bridged

titanocene dich l ~ r i d e . ~ ) C(1) and C(17) of iPr[CpF1u]HfCl2 form an

unusually acute angle of 1 0 1 O with the sp3 C(14) of the iPr bridge.

cyclopentadienyl ligand is slightly distorted. Both the

cyclopentadienyl and the fluorenyl ligands are bent towards Hf,

resulting in their mean planes deviating by 22O and 12O respectively

from the bridgehead to isopropylidene bonds.

The sp2 hybridization at C(1) rules out a

Figure 1 depicts h5 Zr-Flu bonding rather than the more This description was chosen to emphasize

5

from zr comes from the crystal structure of Et[3MeIndI2ZrCl2. 9 )

The order of magnitude higher polypropylene molecular weights

Strained iPr[CpFlu1MCl2 (M - Zr, Hf) complexes. The four

Et[IndI2HfCl2 has no significant distortions relative to

The planar geometry of the bridgehead carbon atom of the

32. Syndiotactic hpyleue Polymerization with iPr[CpFlu]ZrC12 445

Figure 2. Molecular structures for iPr[CpFlu1HfCl2 and Et[IndI2HfCl2.


The views of these two molecules on the right hand side of

Figure 2 show that the C5 rings are eclipsed only in the cage of the more stereorigid iPr bridge and that there is considerable "ring slippage" evident in the iPr[CpFlu1HfCl2 structure. The metal and

its non-cyclopentadienyl ligands protrude considerably more from the

protective network defined by the C5 and C6 ligand rings than in the

case of Et[IndI2HfCl2. This structural difference probably persists

in the active cationic, monoalkyl Zr and Hf species with the same

ligand framework. lo) The non-Cp coordination sites of iPs(CpFlu1M-R+

therefore have a greater potential for exposure to steric effects from

anion associations during polymerization than do the more sterically

shielded, isospecific Et[ Ind12M-R+ intermediates.

with iPr[CpFlu]ZrC12 /MA0 and polymer analyses are in Tables 1 and 2.

Pentane slurry polymerizations are summarized in Table 3. The Zr and MA0 efficiencies are typically high and low

respectively for metallocene catalyzed polymerizations. Maximum

efficiencies were obtained between 60 and 7OOC. The sPP HWDs were 2

and the integral polymerization rates did not have a strong time

dependence. The polymer melting points (mp), syndiotacticity (%r), and

molecular weights (Mv) decrease with increasing temperature; as

expected. The sPP M W s are an order of magnitude higher than for

iPr[IndI2ZrCl2.

relative to Ind. The ligand effects on increasing Mv are Cp < Ind < Flu. The polypropylene molecular weights increase about tenfold for every C6 aromatic ring annelated to the C5 ring.

decrease with decreasing propylene concentration in the pentane slurry

polymerizations summarized in Table 3. The correlation between

propylene and Mv is attributed to a slower propagation rate and a

higher termination rate by B-hydride elimination, due to the

concentration of coordinatively unsaturated intermediates increasing

with decreasing propylene concentration (2, Scheme I).

insertions that are skipped out and hence lower %-r placements and

lower melting points. This aspect is discussed in more detail in the

section on polymer NMR analyses.

Syndiospecific Polymerizations. Bulk polymerization results

This is attributed to increased n-donation for Flu

The sPP molecular weights, %-r placements and melting points

These species also isomerize by chain migration, resulting in

32. SyndwroctiC Pmpylene Polymwizntion with iA.[CpFlu]ZrCl~ 447

a ) Table 1. Polymerization Results with i-PrCpP1uZcCl2

zr, Pol. Eff. Eff. M.F.

( moll TemIoC g/g-Ca t . h g/g-HAO. h g/10 min.

1.3 25 51 , 000 28

0.3 50 194 , 000 33

1.2 60 370,000 200

1 .2b) 70 315,000 340

1

7

13

20

a)Propylene(l.2L);10 mL of 10.7 wt% MAO.b)MAO (5mL)

a ) Table 2. Polymerization Results with i-PrCpFluZrC12

zr, Pol. I O - ~ . M ~ mP 1 r

( moll Temp,OC OC %

1.3 25 212 145 95

0.3 50 133 140 96

1.2 60 129 137

1.2 b) 70 108 134 93

a)propylene(l.2L);10 mL of 10.7 wt% MAO.b)MAO (5 mL)


Table 3. Propylene Polymerizations in Pentane at 65°C.aL)

~

[ C3H6 I , Efficiency, mP I 10-~ii~

M kg/g-cat.h OC

1.3 5 107 51

2.3 8 125 65

3.1 16 131 104

5.2 22 133 109

7.4 78 134 121

9. gb) 369 136 138

89

90

93

94

95

94

"12 mg i-PrCpFluZrC12;5 mL 10.7 wt-% MAO;SOO mL of pentane.

b, 0.5 mg i-PrCpFluZrC12 ; bulk polymerization

The effect of propylene concentration on the active site

concentrations is unknown. No significance is therefore attached to

the questionable influence of propylene concentration on the reaction

rates listed in Table 3 in terms of reaction order in propylene.

Scheme I depicts reversible monome r/iPrCpFluz r-R+ (2) coordination and chain growth (4 to 5 ) by a 1-2 chain migratory insertion with catalyst isomerization from an S to an R configuration. While we know

the structure for 1, the bonding mechanism for 2 is unknown; as is the mechanism of ionization (2 to 21, as well was the structures of the

32. SyndiotcrctiC Propvlene Polymerization W i t h ipICCpFl~lZrC1~ 449

neutral MA0 and its anion. Calculations suggest methyl insertions (4 to S ) , Si,S (i), and Re,R (5) coordinations are all aspecific. 11 1

Scheme I

KC

MA0 i-Pr[CpFlu]ZrMe MA0

2’ 2 i-Pr[CpFlu]ZrMe

1 2 -


C-13 NMR Background. Three microstructures are possible for sPP:

... rrrrrmmrrrrr . . . (I), ... r r r r r m r r r r r . . . (111, and

... rrrrcmmrrrrrmrrrrr... (111).

The isotactic analogs for Structures I and I1 are:

The steric defect shown in the Fischer projection formulae for

Structure 1 is a consequence of reversed enantioface selectivity in an

enantiomorphic site stereochemical control mechanism. The defective

stereochemical placement represents a monomer unit that has been

accidentally enchained "backwards". A random distribution of mm

defects in an otherwise stereoregular syndiotactic chain is the

32. Symliofactic Aopvlene F’olyme7ization with iPrCCpFlulZ~12 451

catalyst’s signature. The defects are consistent with enantiomorphic

site controlled polymerizations.

Meso dyad defects portrayed in Structure 11 have previously been

associated with classical chain end controlled mechanisms of

stereoregulation. However, the m errors are ambiguous. There are

several other reaction mechanisms that can lead to them. The m

placements can, for example, be due to a skipped insertion step in

site controlled polymerizations.

The methyl groups numbered in Structure I11 correspond to the

central methyl carbon of the following pentads and heptads that are

observed by C-13 NMR spectroscopy:

1 - rrrr; 2 - (r)rrrm(m); 3 - rrmm; 4 = rmmr; 5 - (r)rrrm(r);6 = rrmr.

The level of stereochemical defects in highly stereoregular

syndiotactic polymers can be roughly estimated from only two pentads

since mm - rmmr and m - 1/2[xmrx]. The ratio of m to mm varies over a considerable range with differing

catalysts, solvents, temperatures, and monomer concentrations.

Structures approximating both I and I1 have therefore been obtained.

tacticity is shown in Figure 3. Heptad resolution in the syndiotactic

region allows us to distinguish between the methyl groups labeled 2

and 5 in Structure 111. Discussion on the theoretical fit to the two

site model is deferred to the next section.

The prochiral syndiospecific metallocenes produce Structure 111.

A C-13 NMR spectrum of the methyl region f o r sPP with fairly low

Table 4 compares the C-13 NMR pentad intensity measurements with

those expected by simply inspecting Structure 111. The polymer

microstructure can therefore be readily deduced without resorting to

fits of the intensities to statistical structural models. The

excellent agreement between theory and experiment testifies to the

random distribution of the chain stereochemical defects.

C-13 NMR spectra of polymers obtained at 80°C and 2 0 ° C in slurry

polymerizations are contrasted in Tables 5 and 6. These have

... rrrrrmrrrrr... (Table 5, Structure 1 1 ) and ... rrrrrmmrrrrr... (Table 6, Structure I ) microstructures to a first approximation.


1 3 4 3 6 6

... sf-LLhf7 J ._. l+lL& ,.-I...

2 2

Two-Site Model

pentad calc obed A

mmmm mmmr rmmr

mmm xmrx m m r

m rn mrrm

0.000 0.002 0.018

0.036 0.103 0.013

0.697 0.123 0.007

0.000 0.000 0.002 0.000 0.022 0.004

0.046 0.009 0.096 -0.007 0.011 -0.002

0.696 -0,001 0.123 0.000 0.009 0.002 m.d. 0.003

5

rrmr

1

llIlllll 4

I I 5 r = 0.89

rrrr T,= 106OC

1

, . I r,.r--,--r-'77

21.0 20.5 20 .0 19.9

Figure 3. C-13 NMR spectra of the methyl region for sPP obtained at

6 5 O C and 1.3 M propylene in pentane. The fit of the experimental data fortuitously gave f3 as double the value of rmmr.

32. SpdwtoctiC Proprlene Polymeniafion with iPr[CpFlu]ZrCIz 453

Table 4. 13C-NMR spectrum of SPP obtained in pentane at 65DC.a')

methyl obsd structural

group pentad intensity requirement

mmmm

mmmr

(4) rmmr

(3) mmr r

( 6 ) xmrx

mrmr

(1) r r r r

( 2 + 5) rrrm

mr rm

0.000

0.000

0.022

0.040

0.039

0.006

0.827

0.064

0.003

0.020

0.040

0.039

0.822

0.079

"5 M propylene.

Table 5. sPP 13C-NMR spectrum obtained in pentane at BO°C.a)

methyl obsd calc

group pentad intensity intensity

mmmm

mmmr

(4) rmmr

( 3 ) mmr c

(6) xmrx

mrmr

(1) r r r r

( 2 + 5) rrrm

mr rm

0.2

1.0

1.9

6.5

18.2

3.2

49.1

17.74

2.3

0.2

1.2

2.4

4.9

18.2

4.4

49.1

17.5

2.2

a ) 20 psi propylene; m > > mm


Table 6. 13C-NMR spectrum of SPP obtained with iPr[CpFlulZrC12/MA0 at

21OC. a)

methyl obsd structural

group pentad intensity requirement

mmmm mmm c

( 4 ) rmmr

(3) mmr r

( 6 ) xmcx

mrmr (1) r r r c (2 + 5) rrrm

mr rm

0.0

0.0

1.3 2.5

1.3

1.0

90.0

2.8

1.1

- - 1.3

2.5 1.3

- 90.0

3.8

a ) l ~ ~ psi propylene; 2.2 ml 10 wt% MAO; 2 mg iPrCpFluZrC12; 500 ml

toluene; 82 min; 36 g yield.

Microstructure vs Polymerization Conditions. Variation in

the polymer microstructure in bulk as a function of polymerization

temperature and in slurry polymerizations as a function of propylene

concentration are presented in Tables 7 and 8.

A listing of the rrrr pentad along with the two pentad intensity measurements needed to roughly estimate the percentage of m

and mm defects (rmmr and rrmr) are given in Table 7 for samples obtained in bulk polymerizations.

The only other significant defects are very low levels of the

mrmr pentad; as predicted by the statistical and structural models

presented later. The microstructures of all the polymers addressed in

both Tables 7 and 8 consist of blocks of r dyads connected by randomly placed meso triads and dyads (Structure 111).

The temperature dependencies of m (m - 1/2[rrmrl - 1/2[ (r)rrrm(r)]; AAH* = 1.1 kcal/mol; A A S T = 2 eu) and mm (mm - rmmr - 1/2[rrmm] = 1/2[(r)rrrm(m)]; with AAHt - 0.3 kcal/mol; A A S t - -5 eU) show that these two steric defects originate from two entirely

different chemical reactions in the slurry polymerizations.

32. Syndwtactic Pmpulene PolymerLnfion with iPr[CpF1ulZrClz 455

Table 7. C-13 NMR analyses of SPP obtained in bulk.a)

Pol. T I r r r r , rmmr, rrmr,

OC % % %

29 85 1.5 1.2

50 82 1.7 2.8

70 78 1.8 3.6

80b) 49 1.9 18.2

a) Conditions in previous section. b) Pentane; 20 psi propylene; 100

mg iPrCpFluZrCIZ; 5 mL MAO.

Table 8. Analysis of sPP Obtained in Pentane at 65°C.a)

1 [ C ~ H ~ I I r r r r , rmmr , rrmr,

M % % %

1.3 70 2.2 4.8

2.3 82 1.7 2.5

3.1 81 2.0 2.3

5.2 83 2.2 1.6

7.4 84 1.8 1.4

9.gC) 85 2.4 1.3

a ) 2 rng i-PrCpFluZrC12; 5 mL 10.7 wt-a MAO; 500 mL of pentane.

b)Km-[M-C3H6]/[C3H6][M] = 1.3 M-l; "0.5 mg i-PrCpFluZrC12


The slurry polymerization data (Table 8 ) show that the mm

triads do not vary within experimental error with propylene

concentration (mm - rmmr, with an average rmmr - 2 . 0 ) . These

"errors" are interpreted to represent reversed diastereoface

selectivities or enantiomorphic site stereochemical errors.

and increase in melting points (Figure 5 ) with increasing propylene

concentrations are attributed to skipped insertions as a consequence

of coordinatively unsaturated cationic intermediates ( 3 , Scheme I) isomerizing in between monomer additions. The parallel decrease in

molecular weight with decreasing propylene is also consistent with increasing levels of coordinatively unsaturated intermediates leading

to more 0-hydride eliminations and slower propagation rates.

to be roughly 1.3 M-l from the polymer NMR as a function of propylene and with the assumption that the m placements were strictly

attributable to coordinatively unsaturated species.

normal range reported from kinetic measurements with heterogeneous

catalysts but is surprisingly small for a cationic tricoordinate

metallocene.

The asymptotic decrease in meso placements to 1.3% (Figure 4 )

The monomer coordination equilibrium constant was estimated

This Km is in the

The suggestion of a dual rate law with first and second order

dependencies of r/m on propylene concentration (Figure 6) is

consistent with the residual 1.3% m placements in bulk polymerizations

at 65°C being at least partially due to low concentrations of

intermediates with two propylene molecules coordinated simultaneously

on both sides of the growing chain.

There is chemical precedent for pentacoordinate cationic

zirconocenes. 12)

r or to an m placement, depending on the preceding chain end configuration.

Collapse to the right or the left leads to either an

32. SyndwW Aopvkne porvnreriUrtiOn with iPr[CpFlulZrCl2 457

0.050 -

0.040 -

0.030 -

2 0.020 .

xmrx

f 0.010 -

Figure 4. Dependence of meso dyads (m - 1/2[xmXrl) concentration.

rnp, "C

140

130

120

110

100 1 2 3 4 5 6 7 8 9 1 0

0.01 3

1

on propylene

[C3H61p M

Figure 5. Propylene dependence of upper sPP melting points.

158 J . A. Ewcn. M . J . Eldcr. K. I>. Jones. S. Curtis and H. N . Chena

16

1 4

12

10

8

Figure 6. r/m as a function of propylene concentration in pentane

slurry polymerizations: r/m = a[C3H6] - b [ C H 1 2 ; m = 1/2[xmrx]=l-r;

(kp/ki) = 12 for iPrCpFluZr-R+/MAO-. 3 6

32. Syndwktic Ropyhe Polymeriurtion with ipICCpFlulZ~12 459

Isolated competing monomer migratory insertion reactions may also contribute to the residual 1.3 % m dyads. These reactions

theoretically change r/m with no propylene concentration dependence.

polymerization was attributed to competing, slower monomer insertion

reactions for contact ion pair intermediates. Some active sites were proposed to be isospecific due to steric hindrance at one of the two

2b) lateral coordination sites.

Regiospecificty. Figure 7 shows a C-13 NMR analysis of the chain ends for a low molecular weight sample produced in pentane at

8OoC. The vinylidene and n-propyl chain ends are consistent with B- hydride termination and hydride initiations with 1,2-regiospecificty.

The isobutyl groups reflect transfer to A1 and initiation reactions

with methyl groups.

with each other. However, the lower m/r for n-propyl and isopropyl

chain ends shows that insertion by these groups are less

stereospecific than the subsequent propagation rqactions. The bulk of

the inserting alkyl could influence the stereochemistry by having more

rapid migratory isomerization reactions, influencing ion pair

associations, or through non bonded contacts. The low level of regioirregular structures marked with asterisks contrasts with the isospecific metallocene systems.

The low concentration of 2-1 and absence of a 1-3 regio- and

chemical irregularities relative to the isospecific alkyl substituted

Cp and bisindenyl analogs are presumed to be an electronic affect

resulting from the high basicity of the Flu ligand. The more highly

electron deficient isospecific cations are more suitable for 8 - hydride abstractions.

to the main chain shows that the chain end configuration does not

sterically influence chain termination. 1 3 ) Similarly, meso and rac isospecific metallocenes have produced polymers with essentially the same molecular weight .2a) The polymerization and polymer NHR data

accumulated to date are inconsistent with stereochemical influence of

molecular weight.

Isotactic pentads in an otherwise syndiospecific Hf catalyzed

The vinylidene and internal chain m/r content are consistent

The equivalence of m/r for the vinylidene chain ends relative

460 J. A. Ewen, M. J. Elder, R. L. Jones, S . Curtis and H. N. Chew

-CHf -CH-

0 f I 3 (jH3

-C-CHz-CH-cEiz

C

F 3

$3 +3

--ca-cHz-cEI-cH3 4 3 2 1

E-H & T-5 d '

LL -

0.51

0.53

1.03

2

(m / r = 0.17 / 0.83) m / r

1 1

023 1o.n

028 0.72

057 I 0.73

a

Figure 7. C-13 NMR spectrum of a low molecular weight sample of SPP

obtained at 8 0 ° C in pentane at 20 psi propylene.

32. Syndiotacfic P m p y l m Polymerization with iP~CCpFlu1ZrCl~ 461

STEREOREGULATION MODELS

Background. The statistical models derived in this section

account for the methyl pentad distributions in the C-13 NMR spectra

and the sPP microstructures.

Reaction stereoregulation mechanisms have been reduced to

mathematical, kinetic models in several cases. A one-parameter

Bernoullian statistical model14) accounts for the 13C NMR methyl

pentad intensities of both

polypropylenes obtained at subambient temperatures with homogeneous,

achiral catalyst precursors. The polypropylenes have

... rrrrrmrrrrr... and ... mmmmmrmmmmm... microstructures

respectively. 17)

end configurations being responsible for stereoregulation. Two

additional models of the chain-end control type are the first- and the 18) second-order Markovian models.

A one-parameter, enantiomorphic-site control model has been

derived for isospecific polymerizations. A basic assumption in

this model is that the chirality of the catalyst site is responsible

for s te re0 regula t ion. 2o Equations for the enant iomorphi c-si te model

have been derived for stereochemical pentad splitting. 21)

isotactic polymers described by these statistics have an

... mmmmmrrmmmmm... microstructure.

16 1 syndiota~tic'~) and isotactic

The m and r deffects are consistent with the chain-

The

Purukawa's general case, one-site model includes the

influence of the configurations of both the enantiomorphic-site and of

the chain-end unit. 25)

samples of isotactic polypropylene.

characterization of mixtures of atactic and isotactic polypropylene

produced by heterogeneous catalysts 22*23)

of polymers obtained with two soluble catalysts.

chain-end control reactions24) in which the olef in migratory-insertion

was assumed with 2,1-regiospecificity and in which the configuration

of the last inserted monomer unit determines the configuration of the

active sites in a subsequent rapid isomerization step. The satistical

equations for this mechanism are equivalent to those for the chain-end

control, Bernoullian model.

It has not been applied to uncontaminated

A two-site, three-parameter model was used in

and to described a mixture 3 )

Corradini suggested a novel mechanism for syndiospecific


The polymerization conditions leading to the three sPP

microstructures formed by syndiospecific metallocenes cannot be

adequately described with previous statistical models that were

derived for isospecific polymerizations. Indeed, Furukawa has shown

that the enantiomorphic site control model cannot account for polymers 25a with greater than 25 % racemic triads.

Syndiospecific Statistical Models. In the following sections we show that Cossee's chain migratory-insertion mechanism26) leads to

a one-parameter, enantiomorphic-site control model, pentad intensity

distribution equations equivalent to the chain-end control model, a

three-parameter, two-site model suitable for physical mixtures of syndiotactic polypropylene obtained with the above two mechanisms, an

equivalent two-parameter General Case model similar to Furakawa's

model for ipp, and to equations that account for changes in the

polymer microstructure with reaction conditions.

microstructures observed with the sPP polymers with metallocene

catalysts are consistent with site stereochemical control and to

derive the kinetics supporting the proposed chemical reactions

responsible for the m placements.

and Prelog was used to specify the absolute configuration of the

active sites. 27) The ligands were assigned the order of priority

fluorene > cyclopentadiene > polypropylene. The chain-end methine

unit configuration was determined with the priority order CH2-M > polymer > CH3 > H. prochiral faces of the monomer follow IUPAC nomenclature.

The enantioface selectivity of the polymerization is unknown.

It was arbitrarily assumed that non bonded steric forces promote

coordination of the Re face of the monomer at R configuration sites in the derivations that follow. However, reversed enantioface

selectivity leads to the same conclusions.

copolymerization Schemes were selected. The statistical models for

the pentad probability relationships were derived by:

(1) Defining Stereoselective Copolymerization Schemes consistent with the stereochemical events leading to m and r dyads under the restraints of the allowed reactions.

The purpose of deriving these models was to show that the

Stereochemical Nomenclature. The R/S system of Cahn, Ingold

The atom numbering scheme and designation of the 28 1

Statistical Models. Syndiospecific stereoselective

(2) Reducing the number of probabilities for the stereochemical

events to one or two adjustable parameters by identifying equivalent rate constants and rate constant expressions.

( 3 ) Establishing expressions for the probabilities of initiating

stereosequences begining with R and S configurational units.

( 4 ) Deriving the equations for the probability of each pentad as the product of the probabilites for initiation with the probabilities for

addition of each added configurational unit.

derived first. This is regarded as a general structural model for

... rrrrrrmmrrrrrrmrrrrrr.... microstructures. The model applies for

cases in which both the active site and the configuartion of the last

inserted unit influence the stereochemical events (dual control).

The probabilities of initiating stereosequences are the same

as for the isospecific models. However, these parameters are

necessarilly defined and derived differently for the syndiospecific

polymerizations. Additionally, the probability parameters in the

dynamic, syndiospecific copolymerization schemes depend on both the changing configuration of the sites with the monomer coordinated,

prior to insertion, as well as on the stereochemical event.

can be written for a site controlled scheme in which the site undergoes both reverse enantioface selectivity and isomerization

errors. The model is a 2 parameter system. However the equations are

cumbersbm and unwieldy and do not provide more information than can be

extracted directly from the spectra as shown in the preceding section. We have instead derived four simpler cases that are

consistent with the pentad intensity distributions. In the general

case and the two site model we treat the polymers as having an

... rrrrrrmmrrrrrrmrrrrrrr... microstructure and as being a mixture of

... rrrrrmmrrrrr.. and ... rrrrrmrrrrr... polymers. In the final

analysis we simplify the problem by treating the statistics of the m and mm triads individually; assuming the events leading to each of

them are independent of each other. ~t is shown that the variation in the meso placements in the slurry polymerizations with low monomer

concentrations is consistent with isomerization reactions of

coordinatively unsaturated complexes.

The syndiospecific version of the general case model is

A stereoselective copolymerization scheme with 12 equations

464 J. A. Ewen, M. J. Elder, R. L. Jones, S. Curtis and H . N. Cheng

The General Case. It was assumed that the chain growth

mechanism is chain migratory insertion and that the cationic monoalkyl

active sites isomerize with each monomer addition. The configurations

of both the active site and the chain-end are assumed to influence

stereoselectivity in the derivation of this two-parameter model. Eqs 1-8 list all of the eight possible stereochemical events leading to m

and r dyads and the probabilities for each monomer addition.

Scheme 11: Stereoselective Copolymerization for the General Case.

Stereochemical Event Probability

s

s M-S. . . M-S. . .

s

S

M-R.. . M-R.. .

R

R

M-R.. . M-R.. .

R

R

M-S . . . M-S. . .

+ si

+ Re

+ Re

+ si

+ Re

+ si

+ Si

+ Re

R ks M-R-S. . . -SR-

A S - MES-S.. .

R

R

ks M-S-R. . . ks M-R-R.. . - RS-

-RR-

s

S

kR M-S-R.. . M-R-R.. .

-RS-

S

S

kR M-R-S. . . kR M-S-S.. .

-SR-

-SS-

The M superscripts note the absolute configuration of the active

sites. The superscripts attached to the conditional probabilities and the rate constants indicate the chirality of the catalyst prior to

monomer addition. Koenig's conventions have been adopted for the P

and k subscripts.

j chain-end configuartional unit and k indicates that a j unit is incorporated between the catalyst and an i chain-end configuration.

ij Pij notation indicates that an i unit adds to a 2 9 1

tj ij

Si'and Re refer to the prochiral faces of the monomer units that are

coordinated during monomer addition.

relative handedness and the stereochemical outcome of each event

outlined in EqS 1-8 requires that the following relationships hold:

The thermodynamic equivalence of species which differ only in

The probabilities of the events described in Eqs 1-8 can

therefore be described with two parameters, Pa and Pb:

Identical stereosequences are initiated by interntediates that are

oppositely handed in the configurations of both site and chain-end

unit. R and S monomer unit configurations in the polymer are

indistinguishable. The probabilities for pentads in the total polymer

are therefore equal to those of the pentads initiated by either an S

or an R active site with S and R chain-ends. For the sake of brevity, only the events occurring at S configuration sites are considered in the following discussion on stereosequence initiation.

configuration chain-end at S configuration sites, PR , is the mole fraction of R configuration chain-ends at S configuration sites (M-R)

relative to S configuration chain-ends at S Configuration sites (M-S):

The probability of initiating stereosequences with an R s

S

S


[ M% ]

s [M-R] + [MIS]

(15)

The 8 equations in the Scheme I1 were rearranged as shown in

Scheme 111. The concentration of M-S and M-R can be expressed in

terms of each other with K - (1 - Pb)/(l - Pa). The expression for

the equilibrium constant was derived from K = K1.K2 according to the

principal of multiple equilibria.

S s

Derivations of the possible stereochemical arrangements of up to five successive monomer units and the relative probabilities of the

stereosequences initiated at an S configuration site are given in

Tables 9 and 10. The simplified equations containing two adjustable

parameters are given in Tables 11 and 12 for the relative dyad, triad

and pentad intensities for the polymer. They are the sum of the probabilities for that particular dyad, triad or pentad. The

equations are equivalent to the general case in isospecific propylene polymerizations but with m and r reversed. 30 1

Scheme 111

General Case

( l - P b ) R M-S M-S .L S

Chain-End

M-S, S ( 1 - P ) M-S R (1-P)

.1lP p l l p

Site Control and Isomerization Errors (P. p = 0) Enantiomorphic Site

1

468 J. A. Ewen, M. J . Elder, R. L. Jones, S. Curtis and H. N. Cheng

Table 9.a)Dyad and Triad Stereosequences Initiated on S Configuration

Sites and their Probabilities for the General Case Model.

Sequence pi, PYj 9 Probabilities

Pre-Insertion Site

Configuration ( n ) :

- i ij

S R b

Dyads

RR m

RS r

SR r

SS m

Triads

RRR mm

RRS mr

RSR rr

RSS rm

SRR rm

SRS rr

SSR mr

SSS mm

(a) PYj is the probability that an i unit adds t o a j unit at an n configuration S R R R S R R S PRR = Pss= (1-P ); and PRR= P = (l-Pb) a ss site. P SR = P RS- - P PSR' PSR = pb;

The mole fractions of S configuration sites with R and S chain-end

configurations are:

P S S = PR = (1-P ) / ( 2 - P - P,,) and Ps = Ps = (1-Pa)/(2 - Pa- Pb) R b a

(b) The configuration of the active site prior to monomer addition.

Table 10.') Pentad Stereosequerices Initiated on S Configuration Sites and their

Probabilities for CH-CE model.

P" Pentad Probabilities ij'

Sequence Pentad Pi, - 3 - i

Pre-Insertion Site

Configuration (n):b) S R S R

RRRRR

RRRRS

RRRSR

RRRSS

RRSRR

RRSRS

RRSSR

RRSSS

RSRRR

RSRRS

RSRSR

RSRSS

RSSRR

RSSRS

RSSSR

RSSSS

mmmm

mmmr

mmr r

mmrm

mrrm

mrrr

mrmr

mrmm

rrmm

rrmr

rrrr

rrrm

rmrm

rmrr

rmmr

rrmnm

(a) Pn

site. PSR= PRs= Pa; PSR= PSR = Pb; PRR = P ss = (1-P a ); and PRR= Pss= (l-Pb)

is the probability that an i unit adds to a j unit at an n configuration ij S R R R S R R S

The mole~fractions of S configuration sites with R and S chain-end

configurations are:

PR = PR = (1-Pb)/(2 - P a - Pb) and The configuration of the active site prior to monomer addition.

S S Ps = Ps = (1-Pa)/(2 - Pa- Pb) (b)


Table 10. (Continued)

Sequence Pentad Pi, 'Yj 1 Pentad Probabilities

Pre-Insertion Site

Configuration (n): b, S R S R

- i ij

SRRRR

SRRRS

SRRSR

SRRSS

SRSRR

SRSRS

SRSSR

SRSSS

SSRRR

SSRRS

SSRSR

SSRSS

SSSRR

SSSRS

SSSSR

sssss

rmmm

rmmr

rmrr

rmrm

rrrm

rrrr

rrmr

rrmm

mrmm

mrmr

mrrr

mrrm

mmrm

mmrr

mmmr

mmmm

(a) Pyj is the probability that an i unit adds to a j unit at an n configuration S R R R S R R S

site. PSR= PRS= Pa; P SR- - The mole fractions of S configuration sites with R and S chain-end

configurations are:

P

The configuration of the active site prior to monomer addition.

PRR = Pss= (1-P ); and Pm= Pss= (l-Pb) PSR = Pb; a

S S = PR = ( 1 - P b d ( 2 - Pa- Pb) and P S = Ps = (1-Pa)/(2 - Pa- Pb) R

(b)

32. SjdiotaCtic Propvlene pOlvnrerLatim with iPrCCpFln]ZrCl, 471

Table 11. Dyad and Triad Intensities for the General Case Models.

sequence

Dyads

m

r

Triads

mm

mr

K K

Probability


Table 12. Pentad Intensities for the General Case Uodels.

Pentads

mmmm

mmm I:

rmmr

mmr r

mmrm

r rmr

mrmr

rrrr

rrrm

mrrm

Probabilities

(a) The mole fractions of S configuration sites with R and S chain- end configurations are: pR = P: = (1-pb)/(2 - Pa- Pb) and S Ps - Ps - (l-Pa)/(2 - Pa- Pb)

32. SyndiatoctiC Pmpulene PolpnekatMn with ipICCpFlu]ZrC12 473

The two parameters Pa and Pb were calculated with an iterative

fitting procedure at the triad level. The fit of the general case

model to the spectrum of a sample obtained at 70°C is illustrated in

Table 13.

Table 13. Calculated and Measured Band Intensities for SPP Obtained with i-Pr[Cp-l-Flu1ZrCl2 at 70° C.

Band Intensities

Gene r a 1 a') 2 Siteb)

Pentad obsd. Case Model ~ ~~~~

mmmm 0.005 0.001 0.001

mmm r 0.003 0.002 0.002

rmmr 0.018 0.024 0.023

mmr r 0.040 0.048 0.046

xmrx 0.036 0.030 0.039

mrmr 0.017 0.016 0.008

r r r r 0.781 0.808 0.802

rrrm 0.090 0.068 0.074

mr rm 0.009 0.004 0.004

mean deviation 0.009 0.008

')Pa-O.961; Pb-0.302

b)P-0.83; 010.18; 8-0.026


Unfortunately, the magnitudes of Pa and Pb have no physical

significance and reasonably good fits to the experimental data can be

obtained with more than one pair of parameters.

Syndiospecific enantiomorphic site control model. A one-

parameter model is obtained for cases where it is assumed that the

catalyst configuration controls the stereochemical events and that it

isomerizes due to chain migratory-insertion with, and only with, every

monomer addition. It is also assumed in this model that the chain-end

configuration has no control on the stereoregulation kinetics. The

principal stereochemical "errors" generated yield rrrm, mmrr and rmmr

pentads in a 2:2:1 intensity ratio.

Since the chain-end has no influence on stereoregulation

S kRS kzS -

According to Scheme I1

S R R

S R

ka + kb) = Pss PRs PRR (1 - U )

ka + kb) - PRR = P:R - Pss - e

Substituting from Eqs 20 & 21 into Eqs 16 and 17

PS = (1 - a ) , Ps S = 0 R

(20)

(21)

The catalyst and chain end interconversions permitted in

syndiospecific enantiomorphic site controlled stereoselective

copolymerizations are portrayed in Scheme I11 with B - ( 1 - e ) .

summarized under w in Table 14 with B - mm; by analogy with Doi's convention for the isospecific enantiomorphic site controlled

polymerizations. 21)

equivalent to the probability of a site "error" in highly

stereospecific polymerizations where B2- 0.

The triad and pentad equations for this one-parameter model are

This simplifies the pentad equations and makes B

32. Syndwtactic Propylene P o l ~ t i O r r with iPr[CpFlu]ZS12 475

Table 14. Two Site Model Triad and Pentad Intensity Relationships.a)

Sequence weight fraction

W (1-w)

pentad

mmmm

mmm r

rmmr

mmr r

mmrm + rrmr

mrmr

4 B2 (1 - P ) 2 B2 2P(1 - P ) 8 - 3B2

3

2 2 P ( 1 - P)

28 - 6B2 2P2(1 - P)2 4 B2

2 o2

2P(l - PI3 + 2P 3 (1 - P) 2P2(1 - P) 2

rrrr ( 1 - 58 + 5B2) P4

rrrm 2 8 - 602 2p3(1 - P I mr rm B2 P (1 - P) 2 2

a) w = we’ight fraction of syndiotactic polypropylene. 8 is the probability parameter for the syndiospecific enantiomorphic

sites. P is the Bernoullian probability of an r placement for the relatively non-stereospecific sites. B is d e f i n e d h e r e d i f f e r e n t l y than i n t h e t e x t t o s i m p l i f y the pentad e q u a t i o n s . I n t h e Table , B = mm = rmmr; rnr = 28; rr = ( 1 - 3 B ) . 21 1


Chain End Control Model. The general case can be simplified to

Bovey's chain-end control Bernoullian equations. The chain-end

control polymerizations are defined with the following assumptions

From Scheme I11

Substituting from Eqs 25 & 26 into Eqs 11 and 13

S S PSR - Pa - ka/(ka + kb) - PRs - Pb - P Substituting from Eqs 25 & 26 into E q s 16 & 17

- 0.5 S - IM-Slss S

[M-Rlss (28)

The probability of a syndiotactic dyad is

(29) r - [M~S],,PRs + [M-R]ssPSR S - 0.5P + 0.5P - P Triad and pentad equations for the one-parameter Bernoullian

Two-Site Model. A two-site syndiospecific model for a mixture of

model are summarized under (1-w) in Table 14.

polymers produced by a chain end control system and a site control

catalyst is described by the combination of the two models in Table

14. The equations are equivalent to the two site model for

isospecific polymerizations. Applications of this model to spectra

are shown in Table 13 and Figure 3. The parameters have no physical significance and more than one set of parameters can give a

satisfactory solution.

The general case and two site models fit the spectra because they

describe the structure of the polymer. Unfortunately, they have given

satisfactory fits without arriving at a value for 6 that truly reflects the probability of a catalyst error nor the probability of an

isomerization error (1 - Pr). approximate r m m r and (1 - l/2[xmrx]) respectively for the fit listed

in Figure 3. The models are considered unsatisfactory because the parameters have no physical significance.

Site Isomerization Errors. In this section we derive a

hypothetical model to rationalize the decreasing sPP melting points

with decreasing propylene concentrations.

scheme represents polymerizations in which a chiral catalyst only

makes "errors" as a result of site isomerizations.

For example, 6 and Pr do not

Perfect diastereoface selectivity is assumed in Scheme IV. The


Scheme IV: Only Site Isomerization Errors

Stereochemical Event

R

s ks R - R - S . . . R-S. .. + Si -sR--,

I-S-S. . . s

s R-S. . . + Re 3: - s

R

kR M-S-R.. . M - R . . . + Re -RS-

kR R-R-R.. . M - R . . . + Si -i - R

R

In this model

Py - kr/(km + k,) = P: - (1 - P r ) Scheme I11 reduces to

s H i

R z and. Ps - 1.

Probability

(37)

The relative n-ad intensity equations are identical to the chain

end control model with the exception that the rate constants in the

stereoselective copolymerization scheme are pseudo first-order rates

incorporating the concentration of propylene.

The relatively small contribution of the mechanism for m

placements which is second order in propylene is negelected in this

discussion. Considering only the intimate mechanism of stereo-

deregulation as a hypothetical D pathway with a subsequent rate

determining isomerization which is first order in only Zr:

Z $ - R ( C ~ H ~ ) ~ K + Zr- R + C ~ H ~

In Scheme IV.

ky = ki[zrl/(l + K[C3H6])

( 3 8 )

(39)

where ki is the slow isomerization rate constant f o r Zr-R+ and [Zr]

represents the total concentration of Zr. The propagation rate

expression shows that

Dividing equation 40 by equation 39 leads to the prediction of a

linear, direct proportionality between r/m and propylene and the

intercept in Figure 6 gives kp/ki = 12 since K - 1.3 M-'. The slope

in Figure 6 (-0.87) is consistent with similar rates for r and m from

the pentacoordinate intermediate 5.

CONCLUSIONS

The ion pair model is supported by the syndiospecificity of the

polymerizations with the iPrCpF1uZrCl2/MAO system.

microstructures and regiospecificities obtained with unambiguous

syntheses of stereospecific L2Zr-CH3 ion pair catalyst systems also

support this concept.19f2c)

complex are in accord with its syndiospecificty but do not address the 2d, 11) dynamic changes in microstructure with polymerization conditions.

Analogous polymer

+

Models of non-bonded interactions at the

480 J. A. Ewen. M. J. Elder, R. L. Jones, S. Curtis and H . N. Cheng

The contributions to increased MW for the Flu systems compared

with Ind and Cp analogs in terms of stereoregulation of MW and ligand

steric and electronic effects on the termiqation and propagation

reactions have not been determined. If the diastereoface

selectivities for the bisindenyl and Cp/fluorenyl catalyst systems are

the same then the disparity in polymer molecular weights for iPP and

sPP could be partially due to the differing relative handedness for

the metallocenes and chain ends in the catalysts' resting states.

A model assuming that Cp substituents distal to the bridge

experience steric non-bonded contacts with the monomer methyl group,

perhaps mediated by the chain end,"' accounts for the specificity of

the chiral metallocenes that produce isotactic, atactic, syndiotactic,

hemiisotactic, and random or block cotactic polypropylenes. The

tacticities as well as the microstructures of these polymers are

accomodated by these simple concepts, the geometry of the metallocene

ligands, and by generally accepted fundamental aspects of the

polymerization and stereochemical control mechanisms.

ACKNOWLEDGMENT

We thank Dr. J.D. Ferrara, Dr. P.N. Swepston, and Dr. J.M. Troup

of Molecular Structure Corp. for carrying out the crystal structure

studies, Dr J . L . Attwood, Dr. R.L. Jordan, Dr. D. Turner, and Dr. P.

Bradley for consultations, and S.A. Malbari, D. Bartol and E. Zamora

for expert technical assistance.

32. Syndwtactic Propylene PolymerLatMn with iPr[CpFlulZrC12 481

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9.393 ( 6 ) , b = 10.842 ( 4 ) , c = 18.337 ( 4 ) a n g s t r o m s , = 101.92 (3)' , a n d D =

1.424 g/cm3 f o r 2 = 4. r e f l e c t i o n s l e d t o a f i n a l R = 0.051.

L e a s t s q u a r e s r e f i n e m e n t based on 1095 o b s e r v e d

8. The Z r - C J bond d i s t a n c e s r a n g e f rom 2.48 ( b r i d g e h e a d c a r b o n ) to2.63 a n g s t r o m s ( a d i s t a l c a r b o n atom) i n r a ~ - E t [ 3 M e I n d ] ~ Z r C l ~ as a c o n s e q u e n c e o f s ter ic c o n t a c t s be tween 3MeInd and t h e C 1 l i g a n d s , J.A.Ewen, L.H.Haspeslagh, J.L.Atwood

and K.Robinson, u n p u b l i s h e d r e s u l t s . 9. J .A.Smith, J.V.Seyer-1, G . H u t t n e r a n d H . H . B r i n t z i n g e r , J.Organomet.Chem., 173,

175 (1979) 10. R.F.Jordan, C.S.Ba j g u r , W.E.Dasher a n d A.L.Rhiengold, O r g a n o m e t a l l i c s , 6,

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(1980) 16. J.A.Ewen, J.Am.Chem.Soc., 106, 6355 (1984) 17. S t e r e o c h e m i c a l n o t a t i o n proposed by F r i s c h e t al.: H.L.Frisch, C.L.Mallows and

F.A.Bovey, J.Qlem .Phys., & 1565 (1966). P a i r s o f a d j a c e n t m e t h i n e c a r b o n atoms w i t h t h e same r e l a t i v e con f i g u r a t i o n are meso ( m ) d y a d s and p a i r s w i t h o p p o s i t e handedness are r a c e m i c ( r ) dyads .

18. H.L.Fr i sch , C.L.Mallows, F . H e a t l e y a n d F.A.Bovey, Macromolecules , r, 533 (1968) 19. R.A.Sheldon, T.Fueno, T . T s u n e t s u g u a n d J . F u r u k a w a , J.Polym.Sci., 2, 2 3 (1965) ;

R.A.Sheldon, T.Fueno, T.Tsunetsugu a n d J . F u r u k a w a , i b i d . , 1, 7 6 3 (1969) 20. G.Natta, J . Inorg.Nucl .Chem., s, 586 (1958); C.Wolfsgruber , G.Zannoni,

E.Rigamonte and A.Zambelli, Makromol.Chem., 176, 2 7 6 5 ( 1 9 7 5 ) 21. Y.Doi, Makromol.Chem. ,Rapid Commun., 3, 635 (1982) 22. Y.Inoue, Y . I t a b a s h i , R.Chujo and Y.Doi, Polymer , 2, 164 (1984) 23. T .Hayashi , Y.Inoue, R.Chujo and T.Asakura , i b i d . , 3, 138 (1988) 24. P . C o r r a d i n i , G.Guerra and R . P u c c i a r i e l l o , Macromolecules , 12, 42 ( 1 9 8 0 ) 25. ( a ) J . F u r u k a w a , P o l y m e r p r e r p r i n t s , 8, 39 (1967); (b)J.A.Ewen, "Ligand E f f e c t s on

M e t a l l o c e n e C a t a l y z e d P o l y m e r i z a t i o n s " , I n C a t a l y t i c P o l y m e r i z a t i o n o f O l e f i n s ; T.Keii and K.Soga, Eds.; E l s e v i e r , N e w York, 1986

26. P.Cosse, J.Catal., 2, 80 ( 1 9 6 4 ) ; Rec.Trav.Chim.Pays-Bas, E, 1152 ( 1 9 6 6 ) 27. R.R.Cahn a n d C.K.Ingold , J.Chem.Soc., 6 1 2 (1951); R.R.Cahn, C.K.Ingold, V . P r e l o g ,

E x p e r i e n t i a , E 8 1 ( 1 9 5 6 ) ; R.S.Cahn, J.Chem.Educ.. 41, 1 1 6 ( 1 9 6 4 ) , e r r a t u m 508 ( 1 9 6 4 ) ; R.S.Cahn, C.K.Ingold a n d V . P r e l o g , Angew.Chem.Int.Ed.Engl., 5, 385 (1966); K.R.Hanson, J.Am.Chem.Soc., g , 2 7 3 1 (1966)

28. A.D.Jenkins , P u r e Appl.Chem., 2, 1101 (1979) 29. J.L.Koenig, "Chemical M i c r o s t r u c t u r e o f Polymer Chains" , C h a p t e r 3 , J o h n W i l e y

and Sona, New York 1980 30. The p e n t a d e q u a t i o n s r e p o r t e d i n r e f e r e n c e 25b f o r Furukawa 's g e n e r a l case

i s o s p e c i f i c model c o n t a i n errors. The c o r r e c t v e r s i o n c a n be r e a d i l y deduced f rom the e q u a t i o n s l i s t e d i n T a b l e 11. i s o t a c t i c p o l y p r o p y l e n e o b t a i n e d w i t h Et[H4Indl2MCl2 based c a t a l y s t s is i n c o r r e c t . f l a n k i n g 1-3 p r o p y l e n e i n s e r t i o n s b e i n g d e g e n e r a t e w i t h t h e m m m r and m m r m

p e n t a d s : (a)K.Soga, T.Shiono, S.Takemura and W.Kaminsky, Makromol.Chem.,Rapid Commun., 8, 305 (1987) (b)J.A.Ewen and H.N.Cheng, u n p u b l i s h e d r e s u l t s .

A p p l i c a t i o n o f t h e s e p e n t a d e q u a t i o n s t o

The a m b i g u i t y comes from t h e m e t h y l g r o u p s of t h e two monomer u n i t s

483

33. Stereospecific Polymerization of a-Olefin with an Ethylene Bis ( 1 -1ndenyl) Hafnium Dichloride and Methyl-Aluminox- ane Catalyst System

M . K I O K A , T.TSUTSU1, T.UEDA a n d N.KASHIWA

l w a k u n i P o l y m e r R e s e a r c h L a b . M i t s u i P e t r o c h e m . I n d . L t d . ,

W a k i - c h o , Kuga-gun , Y a m a g u c h i - k e n , 7 4 0 , J a p a n

ABSTRACT

S t e r e o s p e c i f i c p o l y m e r i z a t i o n s o f p r o p e n e , 1 - b u t e n e a n d

4 - m e t h y l - I - p e n t e n e w e r e p e r f o r m e d w i t h a n e t h v l e n e b i s ( l - i n d e n v 1 )

h a f n i u m d i c h l o r i d e ( E t ( l n d ) n H f C l z ) c o n t a m i n a t e d b y a s m a l l a m o u n t

o f Z r compound ( 0 . 4 w t X a s Z r a t o m ) i n c o n j u n c t i o n w i t h

m e t h v l a l u m i n o x a n e ( M A 0 ) c o c a t a l y s t a t -10 - 50 c. The m o l e c u l a r w e i g h t o f t h e o b t a i n e d po. lymer d e c r e a s e d w i t h

d e c r e a s i n g p o l y m e r i z a t i o n t e m p e r a t u r e i n t h e c a s e o f p r o p e n e a n d

1 - b u t e n e . I n a d d i t i o n , i n ~ o l y p r o ~ y l e n e t h e b i m o d a l GPC c u r v e s

w e r e o b s e r v e d a t 0 - 20 c , d u e t o t h e Z r compound i n v o l v e d i n

E t ( I n d ) 2 Z r C 12.

F u r t h e r , t h e m e l t i n g t e m p e r a t u r e o f t h e s e p o l v o l e f i n s was

l o w e r t h a n t h a t o f T i C l a - c a t a l y z e d p o l y m e r s a n d t h o s e c a t a l y z e d b y

E t ( I n d 1 Z Z r C 12.

INTRODUCTION

G r e a t i n t e r e s t h a s b e e n f o c u s e d o n t h e s o l u b l e m e t a l l o c e n e /

MA0 c a t a l y s t s y s t e m s i n c e t h e a n n o u n c e m e n t t h a t a s o l u b l e

b i s c y c l o p e n t a d i e n y l z i r u c o n i u m d i c h l o r i d e / MA0 c a t a l y s t s y s t e m p r o -

v i d e s v e r y homogeneous p o l y e t h y l e n e w i t h e x t r e m e l y h i g h

a c t i v i t y . ’ * R e c e n t l y e v e n h i g h l y i s o t a c t i c p o l y p r o p y l e n e h a s b e e n re-

p o r t e d t o b e p r o d u c e d u s i n g E t ( l n d ) n Z r C l z , i t s h y d r o g e n a t e d

c o m ~ o u n d ~ - ~ * o r E t ( l n d ) ~ H f C I ~ 6 * o ’ i n c o n j u n c t i o n w i t h MAO.

484 M. Kioka, T. Tsutsui. T. Ueda and N. Kashiwa

W e h a v e p u b l i s h e d t h e r e s u l t s o f i s o t a c t i c p r o p e n e

p o l y m e r i z a t i o n o v e r a n E t ( 1 n d ) ~ Z r C l n / MA0 c a t a l y s t s y s t e m T ' a n d

o v e r a n E t ( l n d ) a H f C I z / MA0 c a t a l y s t T h e l a t t e r

s t u d y r e p o r t e d t h a t t h e b i m o d a l GPC c u r v e s w e r e o b s e r v e d i n t h e

o b t a i n e d P o l y p r o p y l e n e b y u s i n o a E t ( l n d ) z H f C l z c a t a l y s t c o n -

t a i n i n o 0 . 4 w t X Z r . Two e x p l a n a t i o n s w e r e p r o p o s e d f o r t h i s

o b s e r v a t i o n . i , e . , m u l t i p l e H f a c t i v e s i t e s o r b i m e t a l l i c H f a n d

c o n t a m i n a t i n g Z r a c t i v e s i t e s .

The p u r p o s e o f t h i s p a p e r i s t o c l a r i f y w h i c h o f t h e t w o i s

m o r e P l a u s i b l e a n d t o c o m p a r e t h e p o l y m e r i z a t i o n f e a t u r e s o f

E t ( l n d ) 2 H f C l ~ a n d E t ( l n d ) 2 Z r C l z a s w e l l a s p r o p e n e r i n 1 - b u t e n e

a n d 4 - m e t h y l - I - p e n t e n e p o l y m e r i z a t i o n , b a s e d o n t h e a b o v e

c o n s i de r a t i o n .

EXPERIMENTAL

P r e P a r a t i o n o f E t ( l n d ) 2 H f C I z

T h i r t y - t w o nd o f h e x a n e s o l u t i o n c o n t a i n i n g 50 mmol o f

n - b u t y l I i t h i u m was a d d e d t o a m i x t u r e o f 5 0 nd o f t e t r a h y d r o f u r a n

(THF) a n d 5 . 4 g r a m o f 1,2-bis(l-indenyl)ethaneg' ( E t ( l n d ) ~ )

k e e p i n g t h e t e m p e r a t u r e a t - 3 0 - - 4 0 c . T h e r e a f t e r t h e m i x t u r e

was s t i r r e d a t -30 c f o r 1 h o u r t o o b t a i n t h e THF s o l u t i o n o f t h e

d i l i t h i u m s a l t o f E t ( l n d ) a .

C o m m e r c i a l l y h a f n i u m t e t r a c h l o r i d e ( H f C l s ) s u p p l i e d b y

A l d r i c h w h i c h c o n t a i n e d Z r compound ( 0 . 8 w t X a s Z r a t o m ) was

s l o w l y a d d e d t o 60 d o f THF c o o l e d t o -60 c. T h e r e a f t e r t h e

m i x t u r e was h e a t e d t o 60 c u n d e r s t i r r i n g o v e r 1 h o u r a t 60 c t o

o b t a i n t h e THF s o l u t i o n o f H f C I s .

I n t o t h i s THF s o l u t i o n o f H f C I s THF s o l u t i o n o f d i l i t h i u m

s a l t o f E t ( l n d ) 2 was a d d e d o v e r a 3 0 - m i n . . A f t e r s t i r r i n g a t

60 c f o r 2 h o u r s , t h e s o l i d p a r t was r e m o v e d f r o m t h e l i q u i d

p a r t b y h o t f i l t r a t i o n a t 60c. T h e r e s u l t i n g f i l t r a t e was

c o n c e n t r a t e d t o o n e - f i f t h i t s o r i g i n a l v o l u m e ; t h e y e l l o w s o l i d

was t h e n p r e c i p i t a t e d . The y e l l o w s o l i d t h u s o b t a i n e d was

w a s h e d w i t h h e x a n e a n d d r i e d . T h e r e s u I t i n o s o l i d compound was

f o u n d t o b e E t ( l n d ) n H f C l z c o n t a i n i n o 0 .40 w t X a s Z r a t o m .

33. P o l ~ t i o n of Olefins with Soluble Hf Cutabst 485

P r e p a r a t i o n o f m e t h y l a l u m i n o x a n e (MAO)

M A 0 was p r e p a r e d by a p r e c e d u r e p r e v i o u s l y r e p o r t e d ” a n d

s t o r e d a s t o l u e n e s o l u t i o n a t a c o n c e n t r a t i o n o f 2 . 1 m o l - A I / I .

P o I yme r i z a t i o n o f a - o l e f i n

The p r o c e d u r e f o r p r o p e n e p o l y m e r i z a t i o n was a s f o l l o w s .

F i v e h u n d r e d d o f t o l u e n e , 126 g r a m s o f ~ r o p e n e a n d t h e

p r e s c r i b e d amoun t o f MA0 w e r e p l a c e d i n a 2- 9 s t a i n l e s s - s t e e l

r e a c t o r e q u i p p e d w i t h a s t i r r e r a t room t e m p e r a t u r e . The

p r e s c r i b e d amoun t o f E t ( l n d ) z H f C l z was a d d e d a t t h e p o l y m e r i z a t i o n

t e m p e r a t u r e . P o l y m e r i z a t i o n was c a r r i e d o u t o v e r 0 . 5 t o 4

h o u r s a t a t e m p e r a t u r e r a n g e o f - 1 0 t o 50 c a n d t e r m i n a t e d b y t h e

a d d i t i o n o f a p p r o x i m a t e l y 10 ml? o f m e t h a n o l . T h e e n t i r e

c o n t e n t s w e r e p o u r e d i n t o a p p r o x i m a t e l y 4 o f m e t h a n o l t h e n

d e a s h e d w i t h a m i x t u r e o f h y d r o c h l o r i c a c i d a n d i s o - b u t a n o l .

The r e s u l t i n g p o w d e r y p o l y m e r was c o l l e c t e d b y f i l t r a t i o n a n d

d r i e d i n vacuum a t 80 c f o r 12 h o u r s .

The p o l y m e r i z a t i o n s o f I - b u t e n e a n d 4 - m e t h y l - 1 - p e n t e n e a l s o

w e r e c a r r i e d o u t i n b a s i c a l l y t h e same m a n n e r a s t h e p r o p e n e

p o l y m e r i z a t i o n . D i f f e r e n t c o n d i t i o n s a r e d e s c r i b e d u n d e r e a c h

t a b l e .

13C-NMR aria 1 y s j

The p o l y m e r s o l u t i o n was P r e p a r e d b y d i s s o l v i n g c a . 150 mg o f

t h e p o l y m e r a t 1 2 0 c i n a m i x t u r e o f 0 . 5 d h e x a c h l o r o b u t a d i e n e

and 0 . 1 d d e u t e r i o b e n z e n e . ‘3C-NMR s p e c t r a w e r e r e c o r d e d w i t h

a JEOL-500 s p e c t r o m e t e r o p e r a t i n g a t 125.65 MHz u n d e r p r o t o n n o i s e

d e c o u p l i n g i n F o u r i e r T r a n s f o r m mode .

GPC a n a l y s i s

M o l e c u l a r w e i g h t o f t h e p o l y m e r s a m p l e s was d e t e r m i n e d b y GPC

( W a t e r A s s o c i a t e s , M o d e l / A L C / G P C / l 5 O C ) u s i n g p o l y s t y r e n e g e l

c o l u m n s and o - d i c h l o r o b e n z e n e a s s o l v e n t a t 140 c.

486 M. Kioka, T. Tsutsui, T. Ueda and N. Kashiwa

DSC a n a l y s i s

DSC a n a l y s e s w e r e c a r r i e d o u t b y d i f f e r e n t i a l s c a n n i n g

( P e r k i n E l m e r - 7 ) . T h e c a l i b r a t i o n o f t h e i n s t r u m e n t was

p e r f o r m e d b y m e a s u r e m e n t s o f t h e m e l t i n o p o i n t o f i n d i u m a n d l e a d .

T h e w e i g h t o f t h e s a m p l e was c a . 2 . 5 m e . H e a t r a t e was 10 c / m i n .


I n a P r e v i o u s 6 t U d Y ” t we. p e r f o r m e d P r o p e n e p o l y m e r i z a t i o n

u s i n o a n E t ( l n d ) n H f C I a / MA0 c a t a l y s t s y s t e m . Some o f t h e d a t a

a r e s u m m a r i z e d i n T a b l e 1 t o o e t h e r w i t h t h o s e 7 ’ o f a n a l o g o u s Z r

c a t a l ~ s t ~ a n d GPC d a t a o f t h e o b t a i n e d P o l Y P r o P Y l e n e a r e shown i n

F i o u r e 1 . An i n t e r e s t i n o f a c t i s t h e v a r i a t i o n o f t h e GPC

c u r v e s o f p o l y p r o p y l e n e w i t h p o l y m e r i z a t i o n t e m p e r a t u r e . BY

e l e v a t i n g t h e p o l y m e r i z a t i o n t e m p e r a t u r e 4 a s i n o l e p e a k a t -10 c t u r n e d i n t o a d o u b l e p e a k a t 10 c w i t h t h e a p p e a r a n c e o f a n

a d d i t i o n a l p e a k a t a h i g h e r m o l e c u l a r w e i g h t p o s i t i o n ; t h i s p e a k

g r a d u a l l y s t r e n g t h e n e d b e t w e e n 0 - 20 c a n d was f i n a l l y o b s e r v e d

b y i t s e l f a t o v e r 30 c ( F i g u r e I ) .

T a b l a 1 P r o p e n e P o l i m e r l r a t l o n

Catalrst Temp. Ietal #A0 T i n e Yleld A c t l r l t i I n Ir/In TI am 2.1- 1.3-

C # I mI U r t r/mI-Istal.Hr X I O - ‘ c n n n

Hf / MA0 K O 1.26 6 0.6 29.0 46400 (44800)” 19 2.37 133 92.3 0.7 0.2

SO 1.26 6 0.6 8.1 12900 (11400)’ 16 4.17 135 20 6 10 4 38.4 I900 LO 6 . 8 8 137 93.8 0 . 8 nd

10 6 10 4 1 9 . 8 690 ( 2 2 0 ) * I 1 8.28 139

0 6 10 4 4.4 220 9.9 4.84 142 93.9 0.6 nd

-10 10 10 4 0.9 22 ( O ) * 6.8 2.27 143 94.6 0.6 nd

Zr / I10 60” 1 10 1 82.6 82800 2.0 1.17 131 92.0 0.7 0.1

SO” 1 10 1 67.6 87600 8.2 1.73

10” I 10 I 21.2 21200 4.8 1.77

-10” I 10 8 12.6 2100 6.6 1 . 8 0

1 1 ~ 1 ~ 6-20 > 4 c r . 1 6 0 ca.97 nd nd

I Value fo r . p u r e D Hf catalrrt e s t i m a t e d from Zr c o n t e n t ( 0.022 m o l X ) nd: not d e t e c t e d

33. PolvrneriUrh of Olefins with Soluble Hf Catabst 4117

W e h a v e p r o p o s e d t h a t s u c h i n t e r e s t i ' n o c h a n u e s may b e

e x p l a i n e d b y o n e o f t h e f o l l o w i n g t w o r e a s o n s .

1 ) The e x i s t e n c e o f t w o t y p e s o f H f a c t i v e s i t e s t o p r o d u c e

p o l y m e r s h a v i n g d i f f e r e n t m o l e c u l a r w e i g h t w i t h d i f f e r e n t

a c t i v i t y - t e m p e r a t u r e d e p e n d e n c e .

2) A s m a l l amoun t o f Z r compound i n v o l v e d i n t h e c a t a l y s t s y s t e m

may p r o v i d e a s i u n i f i c a n t amoun t o f t h e l o w e r m o l e c u l a r w e i g h t

~ o l y m e r w i t h much h i g h e r r e l a t i v e a c t i v i t y t o H f c a t a l y s t a t t h e

l o w e r P o l y m e r i z a t i o n t e m p e r a t u r e .

T o e x p l o r e t h e s e t w o a l t e r n a t i v e s we c o n d u c t e d a n a d d i t i o n a l

e x p e r i m e n t .

F i r s t , t h e GPC c u r v e s o f t h e s u b j e c t H f c a t a l y z e d P p l v m e r s a t

10 c and -10 c w e r e c o m p a r e d w i t h those ' ' o f E t ( l n d ) z Z r C l a a t

t h e c o r r e s p o n d i n u t e m p e r a t u r e i n F i g u r e 2, i n d i c a t i n g t h a t t h e Z r

h Polymerlsatlon

103 lo4 105 lo6 lo7 M W

103 lo4 105 lo6 lo7 M W

F l c . 1 CPC Curve8" o f polypropylene obtalnad et Flg.2 Couporlaon of GPC curvee o f polVProPrlene varloum Polvm@rlzrtlon temperaturea rlth Et(1nd):HfCln betreen Et(ln)eHfCI8 contalnlnc 8 amrll OmOUnt Of

contalnlnc ~ D ~ I I amount of Zr compound / Y A O Zr ooipound / YAO and Et(ln):ZrClr / Y A O .


~ o l y m e r e x h i b i t e d a s i n g l e p e a k a t e i t h e r t e m p e r a t u r e , a n d i t s

p o s i t i o n was i n a c c o r d w i t h t h a t o f t h e s i n g l e p e a k o r t h e l o w e r

o f t h e d o u b l e p e a k o f t h e H f p o l y m e r s .

A s s u m i n g t h a t a l l 0 . 4 0 w t X o f Z r c o n t a m i n a t i n g E t ( l n d ) z H f C l z

w o u l d b e Et(lnd)2ZrC1~(0.022mol%) a n d w o r k a s a c t i v e s i t e s , t h e

c o n t r i b u t i o n o f Z r - a n d H f - c a t a l y z e d p o l y m e r s was d e t e r m i n e d b y

c a l c u l a t i o n a n d l i s t e d i n T a b l e 2 . T h e p r o p o r t i o n o f t h e

a m o u n t o f p o l y m e r s w i t h e a c h c a t a l y s t ( P P n r : P P z , ) r e s u l t e d i n

e x c e l l e n t a g r e e m e n t w i t h t h o s e o f t h e p e a k a r e a s i n GPC

( A R E A h l o h r r : A R E A l o w r r ) a t a n y p o l y m e r i z a t i o n t e m p e r a t u r e .

Tabla 2 C o m p r r i a o n of CPPwr:PPz.l *I and C A R E A ~ I . ~ . , : A ~ E A I . . . , I ’I

I n p r o p a n e p o l r a e r l z a t l o n r l t h t h e Hf o r l a i r a t

T e m p . P P W I : P P z r A R E Ahlaher : A R E A I O U . ~

( C )

5 0 4 : a 2 0 : L O O

3 0 1 1 : 8 0 1 2 : 8 8

1 0 8 8 : 3 2 8 4 : 3 8

- 1 0 ( 1 0 0 : 0 ) 1 0 0 : 0

a ) E s t l m r t e d from 2 r c o n t e n t ( 0 . 0 2 2 m o l X as E t ( l n d ) a Z r C l r ) I n t h e

b ) A P E A ~ I . ~ . , r a a d e t e r m l n e d br f o l d i n r t h e c u r v e t r o u r h h i r h e r M I

H f c r t r l r a t and r c t i v i t i e r ” o f E t ( l n d ) e Z r C l n

p o a l t i o n r l o n r t h e l i n e p e r p e n d i c u l a r t o M l a x i s .

N e x t , p r o p e n e p o l y m e r i z a t i o n was c a r r i e d o u t a t 50 c u s i n g

E t ( l n d ) z H f C l n m i x e d w i t h a l a r g e a m o u n t o f E t ( l n d ) z Z r C l z

( Z r / H f = 1 / 2 m , r . I . As shown i n F i g u r e 3 , a new p e a k a t 5 x lo4 o f MW, n o t o b s e r v e d i n t h e p o l y m e r w i t h t h e H f c a t a l y s t (50 ‘C

c u r v e i n F i g u r e l ) , a p p e a r e d a n d r e s u l t e d i n a b i m o d a l c u r v e .

M o r e o v e r , t h e p r o p o r t i o n o f e a c h p e a k a r e a was r o u g h l y 5 0 : 5 0 ,

w h i c h was a l s o i n f a i r a g r e e m e n t w i t h t h e p o l y m e r p r o p o r t i o n

c a l c u l a t e d f r o m e a c h c a t a l y s t a c t i v i t y .

T h e s e r e s u l t s l e d t o t h e c o n c l u s i o n t h a t t h e s e c o n d

e x p l a n a t i o n was m o r e p l a u s i b l e , n a m e l y t h e o b s e r v e d i n t e r e s t i n g

GPC b e h a v i o r was due t o Z r i m p u r i t y , m o s t p r o b a b l y E t ( l n d ) ~ Z r C l ~ ,

i n d i c a t i n g t h a t H f a n d Z r c a t a l y s t s c a n w o r k i n d e p e n d e n t l y o f e a c h

o t h e r i n t h e m i x t u r e .

33. PolymerLotion of Ocefins with Soluble Hf Catalyst 489

~

lo3 lo4 105 lo6 lo7 MW

FI:.~ GPC ourwr of volrprovvlrne obtrlned

Polrrn. Trmp.:SOC r l tb tho olxrd 111/2r( O . 8 W Y / O . 4 r N ) artrlrrt.

B a s e d o n t h i s c o n c l u s i o n ,

10

-to 0 20 40 -t i$' ' ' ' ' *

Polym'n, Temp. ['C] Flr .4 Oelrtlonrhl? betrron polvmrrlzrtlon temverature rad ortrlvrt rotlvltv In propono volvmsrlzrtlon 1 1 t h ~t(lIIdh~fCI8 oontrlnlnr I rial1 rrount o f Zr compound / HA0 and Bt(lnd)tZrClr / HAO. .Pure' 111: ratlirtrd rat1

t h e a c t i v i t y o f

was e s t i m a t e d ( T a b l e 1 ) a n d P l o t t e d i n F i g u r e 4

o f Z r c a t a l y s t , r e v e a l i n g t h a t t h e d i f f e r e n c e

I tr for 'purr. HI ortrlvot

" p u r e " H f c a t a l y s t

t o g e t h e r w i t h t h a t

n a c t i v i t y b e t w e e n

t h e two c a t a l y s t s became much l a r g e r a s t h e t e m p e r a t u r e was

l o w e r e d ( e v e n a t 0 c, Z r a c t i v i t y was m o r e t h a n t w o o r d e r s o f

m a g n i t u d e h i g h e r t h a n t h e a c t i v i t y o f " P u r e " H f , a s shown i n

F i g u r e 4 . T h i s i s t h e r e a s o n why s u c h a s m a l l a m o u n t o f Z r

i m p u r i t y h a d s u c h s i g n i f i c a n t i n f l u e n c e on t h e p o l y m e r i z a t i o n

r e s u l t s a t t h e l o w e r t e m p e r a t u r e .

The m e l t i n g t e m p e r a t u r e o f t h e p o l y m e r a t 50 *c w h i c h was

c o n s i d e r e d t o r e p r e s e n t " P u r e " H f P o l y m e r ' s was n e a r l y t h e same. a s

t h a t o f Z r p o l y m e r . I n e i t h e r c a s e , i t was l o w e r t h a n t h a t o f

c o m m e r c i a l i s o - p o l y p r o p y l e n e p r o d u c e d w i t h T i C l s c a t a l y s t , e * l o '

p e r h a p s due t o t h e d i f f e r e n c e i n s t e r e o s p e c i f i c m i c r o s t r u c t u r e

( T a b l e 1 ) .

The r e s u l t s o f I - b u t e n e p o l y m e r i z a t i o n a r e shown i n T a b l e 3


c o m p a r e d w i t h t h o s e o f E t ( l n d ) ~ Z r C l z . I n t h i s c a s e a l s o , t h e

i n f l u e n c e o f c o n t a m i n a t i n g Z r compound i s s t r o n g l y s u g g e s t e d b y

t h e u n u s u a l d e c r e a s e i n t h e m o l e c u l e r w e i g h t w h i c h a c c o m p a n i e s

l o w e r P o l y m e r i z a t i o n t e m p e r a t u r e i n t h i s r a n e e . T h e a c t i v i t y

o f " p u r e " H f c a t a l y s t was e s t i m a t e d i n t h e same way ( T a b l e 3 ) .

The m e l t i n g t e m p e r a t u r e o f t h e p o l y m e r a t 20 c, v i r t u a l l y

r e g a r d e d t o b e t h a t o f " p u r e " H f , was a b o u t 10 *c l o w e r t h a n t h a t

o f Z r p o l y m e r , u n l i k e P r o p e n e P o l y m e r . A g a i n , b o t h v a l u e s w e r e

c o n s i d e r a b l y lower t h a n t h a t o f T i C I s - c a t a l y z e d i s o - p o l v - 1 - b u t e n e .

Table 3 I-Butane Polrierlzatlon

Catalrrt leap. I e t a l HA0 T i i s Yleld Actlvltr N n TI C IY iH H r I #/mH-#etal.Hr ~ 1 0 ' ~ C

H I / HA0 2 0 0 . 0 0 5 10 2 5 0 . 0 2500 ( 2 2 9 0 ) ' 1 2 . 3 90

10 0 . 0 1 15 2 1 7 . 8 8 8 0 1 0 . 9 93

0 0 . 0 1 1 5 2 6 . 7 280 9 . I 94

-10 0 . 0 1 15 2 1 . 7 8 5 (48)' 6 . 6 9 8

Z r / 110 20 0 . 0 0 2 6 10 2 4 8 . 2 9700 1.2 101

-10 0.0080 I 6 2 2 7 . 0 1700 1 . 4 108

Solvent: 60011 o f toluene. 60011 of I-butane.

x Batlirted value for *pure" Wf catalrst

The r e s u l t s o f p o l y m e r i z a t i o n o f 4 - m e t h y l - I - p e n t e n e a r e s h o w n

i n T a b l e 4 . The e s t i m a t e d " p u r e " H f c a t a l y s t a c t i v i t y i s l i s t e d

i n T a b l e 4 . T h e m e l t i n g t e m p e r a t u r e o f t h e p o l y m e r w i t h " p u r e "

Hf c a t a l y s t was c o n s i d e r e d t o b e a l m o s t t h e same a s t h a t o f Z r

Table 4 4-Methyl-I-Pentene Polrierlzation ~~

Citalurt TIIP. Netal NAO toluene Tlme Y l e l d Actlvltr In TI

c LH .I .B W r I r/iH-Netrl-Hr x I O - ' C

Hf / NAO 30 0 . 1 10 5 0 0 4 S 8 . 9 100 ( 9 1 ) * 1 . 6 3 2 2 0 0 0 . 0 6 5 0 4 1 . 8 9 ( 6 ) * 1 . 5 6 224

~~

Zr / N&O S O 0 . 1 10 500 8 1 2 0 . 8 4 3 0 1 . 1 8 2 2 1

10 0 . 1 6 0 4 24.4 120 1 .00 2 2 7

TIC18 6 ca.240 ~

x Estimated value f o r ' P u r e - H f catmlust. 4-iethvl-I-bentene 50011

33. P o l ~ t i o n of Olefins with Soluble Hf Cutalyst 491

p o l y m e r f r o m t h e d a t a i n T a b l e 48 a n d b o t h v a l u e s w e r e l o w e r t h a n

t h a t o f i s o - p o l y - 4 - m e t h y l - I - p e n t e n e p r o d u c e d w i t h T i C l o c a t a l y s t .

I n t h i s c a s e d e c r e a s e i n t h e m o l e c u l a r w e i g h t o f t h e P o l y m e r was

h a r d l y o b s e r v e d w i t h d e c r e a s i n g t e m p e r a t u r e , d u e t o l i t t l e

d i f f e r e n c e i n t h e m o l e c u l a r w e i g h t b e t w e e n H f p o l y m e r a n d Z r

p o l y m e r .

I n summary, t h e i n t e r e s t i n g b e h a v i o r o f GPC c u r v e s f o r

p o l y ~ r o ~ ~ I e n e o v e r a E t ( l n d ) z H f C l 2 / M A O c a t a l y s t s y s t e m p r e p a r e d

w i t h c o m m e r c i a l l y a v a i l a b l e H f C 1 4 may b e a t t r i b u t a b l e t o t h e

p r e s e n c e o f a s m a l l amoun t o f c o n t a m i n a t i n g Z r compound d e r i v e d

f r o m t h e Z r - i m p u r i t y i n H f C I 4 . T h e s t e r e o s p e c i f i c P o l y m e r s o f

P r o P e n e r 1 - b u t e n e a n d 4 - m e t h y l - 1 - p e n t e n e o b t a i n e d w i t h t h e H f

a n d / o r Z r c a t a l y s t s y s t e m w e r e c h a r a c t e r i z e d b y lower m e l t i n g

t e m p e r a t u r e c o m p a r e d w i t h T i C l s p o l y m e r s , p e r h a p s d u e t o

d i f f e r e n c e i n s t e r e o s p e c i f i c m i c r o s t r u c t u r e .

R e f e r e n c e s

1 . W . K a m i n s k y , T r a n s i t i o n M e t a l C a t a l y z e d P o l y m e r i z a t i o n , V o 1 . 4 8

A l k e n e s and D i e n e s ( E d . R . P . Q u i r k ) H a r w o o d , New Y o r k ( 1 9 8 8 )

2 . W.Kaminsky , K . K u l p e r , H . H . B r i n t z i n g e r and F . R . W . P . W i I d 8 Angew.

Chem. I n t . E n g l . , 24, 5 0 7 ( 1 9 8 5 )

3 . W . K a m i n s k y 8 K . K u l p e r a n d S . N i e d o b a , M a k r o m o l . C h e m . , M a c r o m o l .

S v m P . , 3, 3 7 7 ( 1 9 8 6 )

4 . W . K a m i n s k y C a t a l y t i c P o l y m e r i z a t i o n o f O l e f i n s ( E d s . T . K e i i a n d

K . S o g a ) K o d a n s h a a n d E l s e v e r ,

5) J o h n A.Ewen, L . H a s p e s l a g h 8 J e r

J . A m . C h e m . S o c . , 109, 6 5 4 ( 9 8 7

6. J o h n A.Ewen, L . H a s p e s l a g h , M . J

H . Z h a n g a n d H . N . C h e n o , T r a n s i

T o k y o 8 Amste rdam, ~ 2 9 3 ( 1 9 8 6 )

Y L . A t w o o d a n d H . Z h a n g 8

E l d e r , J e r r y L . A t w o o d ,

i o n M e t a l s a n d O r o a n o m e t a l l i c a s

C a t a l y s t s f o r O l e f i n P o l y m e r i z a t i o n ( e d s . W.Kaminskv , H . S i n n )

S p r i n g e r - V e r l a g , B e r l i n , ~ 2 8 1 ( 1 9 8 8 )

7 . T . T s u t s u i , N . I s h i m a r u , A . M i z u n o 8 A . T o ~ o t a a n d N . K a s h i w a ,

P o l y m e r , 3 0 , 1 3 5 0 ( 1 9 8 9 )


8 . A . T o v o t a , T T s u t s u i and N . K a s h i w a , J . M o l . C a t a l . i n p r e s s

9 . E . M a r e c h a l and A . l e p e r t , B u l l . S O C . C h i m . , 2954 (1967)

493

34. Isotactic Polypropylene with a Soluble Metallocene Based Catalyst System- Characterization of Blown Film-

T.TSUTSU1, M.KlOKA, A.TOYOTA and N.KASHIWA

lwakuni Polymer Research Laboratories, Mitsui Petrochqmical Indus-

tries, Ltd., Waki-cho, Kuoa-gun, Yamaouchi-kenr 740 Japan

ABSTRACT

A blown fi I m

an ethylene bis(

methylaluminoxane

of isotactic homo-polypropylene (PP) obtained with

-Indenyl)hafnium dichloride in conjunction with

nas characterized by its mechanical and thermal

Properties in comparison with those of commercially available homo-

and random-PP obtained with a Ti catalyst system. Consequentlyl the

film with the Hf eystem was found to show oonsiderably different

operties from homo P P film with the Ti system and relatively

milar properties to random P P film with the Ti system. This is

obably due to the differences and similarities in the

crostructure of polymers.

INTRODUCTION

I t has been reported that soluble metallocene compounds such as

Ti, Zr and Hf havino a chiral Iioand, 8.0. ethylene b i s ( l - i n d e n ~ l ) or

its hydrogenated compound, and a methylaluminoxane (MAD) catalyst

system produoes isotaotio p o l y p r o ~ y l e n e (PP). In particular, using

the Zr or Hf compoundr PP havino hioh isotacticity comparable to

oommercially available P P can be obtained.'-"' Furthermorer the

microstructure and thermal properties of the P P have been investi-

gated.a-o' However, there are no reports reoardino their film

Properties.

In this paper, a blown film of P P obtained with an ethylene

b i s ( l - i n d e n ~ I ) hafnium d i oh I or i de (Et ( I nd)zHfClz) and an M A 0 cata I yst

system was Produced and its properties were investigated.

EXPERIMENTAL

P-: In a 2 L stainless steel reactor equipped with a

494 T. Tsutsui, M. Kioka, A. Toyota and N. Kashiwa

s t i r r e r , 7 5 0 m i o f t o l u e n e was p l a c e d a t room t e m p e r a t u r e and

s a t u r a t e d w i t h p r o p y l e n e . T h e s y s t e m was h e a t e d t o 45 'Ct t h e n 7 . 5

m m o l o f M A 0 t o l u e n e s o l u t i o n as A l a t o m and 1.88 f i mol o f

E t ( i n d ) z H f C l z ( c o n t a i n i n g 0.40 w t X o f Z r a s c o n t a m i n a n t ) t o l u e n e

s o l u t i o n as H f a t o m w e r e a d d e d . P o l y m e r i z a t i o n s w e r e c a r r i e d o u t a t

50'C f o r 30 m i n u n d e r 8 k g / c m z t o t a l p r e s s u r e . P r o ~ ~ l e n e was

c o n t i n u o u s l y s u p p l i e d t o k e e p t o t a l p r e s s u r e a t 8 k a / c m 2 . A f t e r 30

mint a s m a l l amount o f m e t h a n o l was a d d e d i n t o t h e s y s t e m t o

t e r m i n a t e P o l y m e r i z a t i o n . T h e w h o l e p r o d u o t s w e r e p o u r e d i n t o a l a r g e

amoun t o f m e t h a n o l a n d d e a s h e d w i t h a m i x e d s o l u t i o n o f h y d r o c h l o r i c

a c i d and i s o b u t a n o l . The r e s u l t i n g ~ o l y m e r s w e r e c o l l e c t e d b y

f i l t r a t i o n and vacuum d r i e d a t 80'C f o r 12 h . The s a m e o p e r a t i o n was

r e p e a t e d 4 t i m e s , r e s u l t i n g i n c a . 400 9 o f y i e l d . T h e o b t a i n e d

p o l y m e r s w e r e b l e n d e d w l t h a e t a b i l i z e r a n d p e l l e t i z e d u s i n g a n

e x t r u d e r a t a b a r r e l t e m p e r a t u r e o f 200'C.

P r o c e s s i n g I n t o b l o w n f i l m s : The f i l m s ( t h i c k n e s s c a . 30 f i m ,

w i d t h 2 0 cm) w e r e p r o d u c e d u s i n g a n e x t r u d e r ( B r a b e n d e r 20 m m # 1

u n d e r t h e f o l l o w i n g c o n d i t i o n s : b a r r e l t e m p e r a t u r e 2 0 0 - 230'C, d i e

t e m p e r a t u r e 230'C, e x t r u d i n g r a t e c a . 20 g / m i n , a i r c o o l i n g a t room

t e m p e r a t u r e .

C h a r a c t e r l z a t i o n of f i l m s: The m e l t i n g p o i n t was m e a s u r e d b y DSC

( P e r k i n E l m e r DSC 7, s c a n n i n g s p e e d + I O ° C / m i n ) . W i d e - a n g l e X - r a y

d i f f r a c t o o r a m s and t h e d y n a m i c - m e c h a n i c a l r e l a x a t i o n s p e c t r a w e r e

o b t a i n e d b y R i g a k u RU-300 d i f f r a c t o m e t e r (Cu K a N i - f i l t e r e d

r a d i a t i o n , 50 kVI 300 mA, s c a n n i n g r a t e 2 ' /min) a n d b y R h e o v i b r o n

v i s c o e i a s t m e t e r DDV-2-A o f T o y o I n s t r u m e n t ( v i b r a t i o n a l f r e q u e n c y 110

Hz, t e m p e r a t u r e r a n g e -160 t o 150'C), r e s p e c t i v e l y . The t h i c k n e s s o f

l a m e l l a was m e a s u r e d b y L a s e r Raman S p e c t r o m e t r y (JEOL JRS-4OOT).

T e n s i l e s t r e n g t h t e a t a n d i m p a c t r e s i s t a n c e t e s t o f t h e f i l m s

w e r e p e r f o r m e d a t 23'C a c c o r d i n g t o ASTM D638 a n d D256, r e s p e c t i v e l y .

C o n d i t i o n s o f t h e h e a t s e a l a b i l i t y t e s t w e r e a s f o l l o w s : w i d t h o f

s p e c i m e n 15mm, s e a l i n g P r e s s u r e 2ko /cmo l s e a l i n g t i m e 1 s e c o n d . H e a t

s e a l a b i l i t y was e s t i m a t e d b y d e t e r m i n i n g t h e l o w e s t t e m p e r a t u r e a t

w h i c h s e a l e d s t r e n g t h was m o r e t h a n 800 g .


P o l y m e r i z a t i o n s o f P r o p y l e n e w e r e c a r r i e d o u t 4 t i m e s u n d e r t h e

same c o n d i t i o n s w i t h t h e c a t a l y s t s y s t e m c o m p r i s i n g E t ( l n d ) n H f C l n and

MAO, r e s u l t i n g i n 400 g o f i s o t a c t i o h o m o - P o l y p r o p y l e n e ( P P ) . The PP

34. Isotactic PP with Soluble MetaNoCene-&lsed Gatahst System 495

o b t a i n e d was b l e n d e d w i t h a s t a b i l i z e r and p e l l e t i z e d b y a n e x t r u d e r .

A n a l y t i c a l d a t a o f t h e p e l l e t i z e d PP a r e ehown i n T a b l e 1 . F o r

c o m p a r i s o n , a c o m m e r c i a l g r a d e homo-PP (F-300, M i t s u i P e t r o o h e m i c a l

I n d . ) p r o d u c e d w i t h a h i g h l y a c t i v e a n d h i g h l y s t e r e o s p e c i f i c M g C l n

s u p p o r t e d T i c a t a l y s t s y s t e m was e m p l o y e d . The r e s u l t s a r e l i s t e d i n

T a b l e 1 .

F o r homo-PP w i t h t h e H f s y s t e m , t h e v a l u e o f 1 . 1 . 8 d e f i n e d as

t h e w e i g h t f r a c t i o n o f b o i l i n g h e p t a n e - i n s o l u b l e p o r t i o n , was v s r y

l o w (38 .3%) c o m p a r e d w i t h t h a t o f t h e T i s y s t e m ( 9 8 . 3 % ) , w h i l e t h e

meso-meso v a l u e m e a s u r e d b y ' V - N M R was m e r e l y 5% l o w e r t h a n t h a t o f

t h e T i s y s t e m ( 9 7 . 3 % ) . F r o m t h e s e d a t a , t h e H f c a t a l y z e d homo-PP i s

c o n s i d e r e d t o b e i s o t a c t i c PP h a v i n g h i g h s o l u b i l i t y i n b o i l i n g

h e p t a n e .

N e x t , t h e b l o w n f i l m s ( c a . 30 L1 m t h i c k n e s s ) o f PP w i t h t h e H f

and T i s y s t e m s ( h e r e a f t e r c a l l e d H f h o m o - f i l m and T i homo- f i l m ,

r e s p e c t i v e l y ) w e r e p r o d u c e d , f o l l o w e d b y t h e c h a r a c t e r i z a t i o n .

The m e l t i n g p o i n t o f t h e H f h o m o - f i l m was 1 3 3 . 7 ' C I c o n s i d e r a b l y

l o w e r t h a n t h a t o f t h e T i h o m o - f i l m ( 1 6 4 . 1 ' C ) .

F i g u r e . 1 shows t h e w l d e - a n g l e X - r a y d i f f r a c t i o n s p e c t r a o f t h e

f i l m s . The s p e c t r a a r e a l m o s t t h e same and i n d i c a t e a n Q - f o r m f o r

t h e c r y s t a l f o r m o f PP. F r o m t h e i n t e n s i t y o f t h e s ~ e c t r a ~ t h e

c r y s t a l l i n i t y was c a l o u l a t e d t o b e 43.7% and 5 0 . 5 % f o r t h e H f and T i

h o m o - f i l m s , r e s p e c t i v e l y . F u r t h e r m o r e , b y L a s e r Ramen A n a l y s i s , t h e

t h i c k n e s s o f t h e l a m e l l a f o r t h e H f h o m o - f i l m was d e t e r m i n e d t o b e 85

A , 10 A t h i n n e r t h a n t h a t o f t h e T i h o m o - f i l m (95 A 1 . Thus, t h e

l o w m e l t i n g p o i n t o f t h e H f h o m o - f i l m i s c o n s i d e r e d t o b e due t o t h e

c o m b i n a t i o n o f t h e l o w e r c r y s t a l l i n i t y and t h e t h i n l a m e l l a , b u t n o t

t o t h e d i f f e r e n c e i n c r y s t a l f o r m .

T a b l e 2 shows d a t a o n t h e m e c h a n i c a l and h e a t s e s l a b l e

p r o p e r t i e s o f t h e f i l m s 8 l.e. s t i f f n e s s b y t e n s i l e y i e l d s t r e s s ( Y S )

and t e n s i l e s t r e n g t h (TS) , t o u g h n e s s b y f i l m i m p a c t s t r e n g t h , and

h e a t s e a l a b i l i t y .

The v a l u e s o f YS a n d TS f o r t h e H f h o m o - f i l m w e r e l o w e r t h a n

t h o s e f o r t h e T i h o m o - f i l m , i n d i c a t i n g t h a t t h e f o r m e r i s s t i f f e r .

T h i s i s a t t r i b u t a b l e t o t h e l o w e r c r y s t a l l i n i t y o f t h e H f h o m o - f i l m .

The i m p a c t s t r e n g t h o f t h e H f h o m o - f i l m was h i g h e r t h a n t h a t o f

t h e T i h o m o - f i l m .

F i g u r e . 2 shows t h e d y n a m i c - m e c h a n i c a l s p e c t r a o f t h e two f i l m s .

T h e r e was n o s i g n i f i c a n t d i f f e r e n c e i n t h e v a l u e s o f t a n 6 a t i t s

496 T. Tsutsui, M. Kioka, A. Toyota and N. Kashiwa

Table 1 . Analvtical data of homo-PP

Hf 2 . 8 1 3 8 . 3 9 2 . 6

114’ 3 . 0 1 9 8 . 3 9 7 . 3 ~ ~ ~~~

Intrinsic vlsoosltv measured in decallne at 1 3 6 C

O ) Weight fractlon o f boiling heptane insoluble polymer

a ’ meso-meso triad sequence content by “C-NMR (126MHz)

‘ ) F-SOO(horo-PP) of Witsui Petrochemical Ind., Ltd.

Table 2 . Properties of Hf and Ti homo-films

Hf Ti

Helting point ( C ) Crvstaliinlty ( %

Thickness of lamella ( A > Y S ( I )/(II) (kr/cm*

T S ( I > / < I I ) (kr/cm*

EL ( I ) / ( I l l ( % 1 Impact strength (kg*cm/ci)

HST (C)

1 3 3 . 7

4 3 . 7

8 6

2 6 6 / 2 4 6

4 1 8 1 3 2 6

6 0 6 / 2 2 0

4 4 6

140

1 6 4 . 1

6 0 . 6

96

4 1 6 / 3 9 6

7 4 0 / 6 0 6

6 7 6 / 0 16

207

160 ~

Y S : Tensile yield stress TS: Tensile strength

EL: Eionration

( I ): Measurement value for direction of tenslle

(II 1: Yeasureient value for transversal direction t o ( I ) HST: Lowest heat seaiabie temperature at rhlch sealed

strength is more than 800 g

34. Isokrcfic PP with Soluble Metalbcene-Based Catalyst Systnn 497

I 1 1 I I 1

30 20 10 30 20 10

280 280

Figure 1. Wide-angle X-ray diffraction spectra

(left) Hf homo-film (right) Ti homo-film

10

w 9 rn 0 cl

8

-100 0 100 200

Temperature ( " C )

0

W

-l 3 CI

s" - 2

Figure 2. Dynamic-mechanical spectra

- I Hf homo-film ,....... ". a Ti homo-film

Two upper curves and two lower ones show E in dyn/cm2 (storage modulus) and tan 6 (loss factor), respbctively.

498 T. Tsutsui, M. Kioh, A. Toyota and N. Kashiwa

maximum, w h i c h i s a s s o c i a t e d w i t h g l a s s t r a n s i t i o n t e m p e r a t u r e ( T o ) .

Thus , t h e a b o v e d i f f e r e n o e i n f i l m i m p a c t s t r e n g t h is n o t due t o t h e

d i f f e r e n c e i n T o .

The h e a t s e a l a b i l i t y o f t h e f i l m s was e v a l u a t e d b y d e t e r m i n i n g

t h e l o w e s t t e m p e r a t u r e (HST) a t w h i c h t h e c l e a l e d s t r e n o t h r e a c h e d

m o r e t h a n 800 g . The H f h o m o - f i l m showed 140’C HST, 20’C l o w e r t h a n

t h a t o f t h e T i h o m o - f i l m , m a i n l y d u e t o t h e d i f f e r e n c e I n t h e m e l t i n g

p o i n t .

F r o m t h e a b o v e f e a t u r e s , t h e H f h o m o - f i l m i s c o n c l u d e d t o h a v e

p r o p e r t i e s c l e a r l y d l f f e r e n t f r o m t h o s e o f T i h o m o - f i l m .

W e h a v e r e p o r t e d t h e e x i s t e n c e o f n o n r e g i o s p e c i f i c p a r t s ( 0 . 4 - 0 . 9 moi X o f h e a d - t o - h e a d o r t a i l - t o - t a i l u n i t a n d 4CHnS4 u n i t ) i n

homo-PP o b t a i n e d w i t h a n E t ( l n d ) n H f C l n and MA0 c a t a l y s t s Y s t e m . ’ O ’

The s t r u c t u r e c o n t a i n i n g t h e a b o v e n o n r e g i o s p e c i f i c u n i t s i s somewhat

s i m i l a r t o t h a t o f a random c o p o l y m e r p r o d u c e d b y c o p o l y m e r i z a t i o n o f

p r o p y l e n e and a s m a l l amoun t o f e t h y l e n e w i t h a T i c a t a l y s t s y s t e m .

A c c o r d i n g l y , t h e f i l m p r o p e r t i e s o f a c o m m e r c i a l g r a d e random

c o p o l y m e r (8-230 o f M i t s u i P e t r o c h e m i o a l Ind.8 e t h y l e n e c o n t e n t 4

molX) p r o d u c e d w i t h a T i c a t a l y s t s y s t e m ( h e r e a f t e r c a l l e d T i

r a n d o m - f i l m ) w e r e a l s o i n v e s t i g a t e d i n t h e s a m e m a n n e r as t h e

h o m o - f i l m s . The r e s u l t s a r e l i s t e d i n T a b l e 3. BY t h e i n t r o d u c t i o n

o f e t h y l e n e u n i t s i n t o t h e p o l y m e r c h a i n , m e l t i n g p o i n t (164.1 +

1 4 6 . 9 ’ c ) , crystallinity ( 6 0 . 6 + 4 6 . 6 % ) , lamella t h i c k n e s s ( 9 5 + 8 5

Table 3. Properties of TI random-film”

Yeltlnc point (C 1 Crvstalllnltv ( % 1 Thlckneee of lamel Is ( A ) YS ( I > / < n 1 (ke/cm* 1 TS ( I > / < n 1 (kc/cm* 1 EL ( I )/(Ill ( % 1 Impact atrenrth (kg *CI/CI)

HST (C 1

148.9

4 8 . 8

8 6

300/ 23 6

886/336

4 2 0 / 6 0 6

60 2

160

1 ) B-230(random-PP) o f Mlteul Petrochemlcrl Ind.,Ltd.

ethylene content 4 mol X , C I I 1 3.89 dl/g

34. IsokrctiC PP with Soluble MehNacene-Based Cutahst System 499

A 1 1 stiffness ( e x . 415 -* 300 ko/cm2 in YS) and HST (160 + 150.C)

were lowered, w h i l e toughness (207 + 602 ko*cm/cm) w a s enhanced in

comparison w i t h the Ti homo-film. T h e s e differences between Ti

random- and homo-filme a r e similar to those between Hf and Ti

homo-films.

I t can be conoluded that for film properties, the above

nonreoiospecific units play a role similar to that o f ethylene u n i t s

in the random c o ~ o l y r n e r ~ but their efficiency with reoard to changes

in film Properties i s slonlficantlv different.

REFERENCES

I . John A.Ewenl J.Am.Chem.Soc., m, 6355 (1984) 2 . W.Kaminsky, K.Kulper, H.H.Brintzinoer and F.R.W.P.WiIdt

Anoew.Chem.Int.Ed.Enol., 24, 507 (1985) 3. W.Kaminskv, K.Kulper and S.Niedoba, Makromol.Chem.0

Macromol.Svmp.8 3, 377 (1986) 4. W.Kaminsky "Catalytic P o l y m e r i z a t i o n of Olefins" (Eds. T.KeiI

and K.Sooa) Kodansha and Elsevier, Tokyo, 1986, ~ 2 9 3

5 . John A.Ewent L.Haspeslaoh, Jerry L.Atwood and H.Zhano,

J.Am.Chem. S O D . , 1p9, 6544 (1987)

6. K.Sooa, T.Shiono, S.Takemura and W.Kaminskv, Makromol.Chem.#

Rapid C o m m u n . r 8, 305 (1987) 7. A.Grassi, A.Zambelli, L.Rescon1, E.Albizzat1 and R.Mazzocch1,

Macromolecules, 21, 617 (1988) 8. T.Tsutsui, A.Mizuno and N.Kashiwa, Makromol.Chem., 1 9 p t 1177

( 1 989)

9 . T.Tsutsui, N.Ishimaru, A.Mizuno, A.Tovota and N.Kashiwa,

Polymer, a, 1350 (1989) 10. A.Toyota, T.Tsutsui and N.Kashiwa, J.Molecular Catalysis,

in press


501

35. Propylene Polymerization by Stereorigid Metallocene Catalysts : Some New Aspects of the Metallocene Struc- ture/Polypropylene Microstructure Correlation

M. Antberg, V. Dolle , R. Klein, J. Rohrmann, W. Spaleck and A. Winter

HOECHST AG

6230 Frankfurt a. Main 8 0 , FRG

ABSTRACT

To obtain highly isotactic polypropylene chiral

metallocenes have to be used. In this work it is shown that chirality is a necessary but not sufficient condi-

tion f o r high isospecifity. Variation of metallocene structure retaining chirality can lead to strongly re-

duced isospecifity: Breakdown of stereospecifity by

slight structural variation can also be demonstrated

with syndiospecific metallocene catalysts.

INTRODUCTION

In our laboratory a series of experiments have

been carried out to study the metallocene structure / polypropylene microstructure correlations by variation

of metallocene structure. The use of stereorigid metallocenes as catalyst can help to understand the reasons

for stereospecific polymerization of propene in more detail 4 ) .

502 M. Antberg, V. Dolle. R. Klein, J. Rohrmann, W. Spaleck and A. Winter

The first metallocene which could polymerize pro-

pene to highly isotactic polypropylene was

bis(tetrahydroindenyl)-ethylene-zirconiu-dichloride

(1) and was published in 1985 by Brintzinger and Ka-

minsky l). It' s x-ray structure shows a perfect Cz-sym-

metry (fig. 1).

b

fig. 1: rtructuro of ethylen. bis(4,S,6,7 tetrahydro-1-indenyl) rirconiun dichlorido

EXPERIMENTAL

The chemicals used are: methylaluminoxane supplied

by Schering, Bergkamen (FRG) , propene (polymerization grade) was dried by passing over a molecular sieve co-

lumn, oxygen was removed by a column filled with BTS-

catalyst (BASF AG, Ludwigshafen FRG). A typical syn-

thesis of a metallocene is given in the appendix A.

For further synthesis procedures see ref. 7. The

polymerization conditions for all the experiments are

as follows: Liquid propene, 6 mmol A1 /1 (as

methylaluminoxane = MAO), polymerization temperature

70' C, polymerization time one hour. The reactor used

is a 16 ltr. steel vessel. The general polymerization

35. f b p y h e PolymerLnfion by Stwm'gid Metallocene Catalysts 503

procedure is given in appendix B. The 13C-NMR analyses

have been carried out on Bruker WP 300 spectrometer,

the molecular mass distributions have been analysed

using a Waters 150-C (Millipore) chromatograph.

RESULTS

First experiments to modify the metallocene struc-

ture starting from 1 by replacing the ethylene bridge by a one-membered dimethylsilylbridge (2) lead to a metallocene of the same symmetry (fig. 2 ) and spatial ar-

ranqement 5 ) .

2 -

f ig . 2: structure of bis(l-indenyl)-dinethyl- silyl-zirconiut dichlorida

This system will be used as a reference compound

for the following discussion.

Typical performance data in propene bulk poly-

merizations of compound 2 and all other compounds to be described using methylaluminoxane as c'ocatalyst are

listed in table 1.

The generally possible variations of metallocene

structure starting from the reference compound (2) are listed in figure 3 .

504 M. Antberg. V. Dolle. R. Klein. J. Rohrmann. W. Spaleck and A. Winter

central metal

/ \ Zr Hf

bridge between cyclopentadienyl rings

/\ shorter longer

ligand system

loosing chirality

retaining chirality

loosing /-\

retaining C2 -symmetry C 2 -symmetry

ligand system (mirror symmetrical compounds)

retaining symmetry d/ modifying symmetry by substituition

fig. 3: possible structural modifications

tab le 1: performance data

corn- a c t i v i t y polymer polydis- isotaOfi2 qs0* nsyn** pound [kg PP/ molecular pers i ty index

mu01 Zr/h] maas (%&I If (2.1

156 20000 2 93.1 56.0 2 2 112 ssooo 2 92.7 50.0 2 1

27 lS000 2 60.0 11.5 2 6.8 7000 2 46.5 2.3 2.4

1

6.3 17000 2 69.0 4.6 2 4

56 84000 2 94.6**', 1.6 25 I 6

B x 0.1 llOOO+ 2.3 56.0 2.9 2 - 7 4.8 5000 2 49.5 3.8 3.8

niso ; 1 + (2mm / m r ) ** n 1 + (2rr / iur) + dimension: kg PP / mmol Hf /h *** zp: syndiotactic index

**** from L~C-NMR:: II = nun + mr/2

35. Propylene PolymenkriOn ly Stereorigid Metallocene Catalysts 505

There are three main units to be varied:

1) the central metal

2 ) the bridge

3 ) the aromatic ligands.

The influence of the central metal is well known

from the work of Ewen 2 ) . Therefore only modifications

of the bridge and the aromatic ligands have been car-

ried out.

Possible modifications of the bridge will change

the spatial arrangement of the system and maybe the

electronic structure, the chirality being retained.

Variation of the aromatic ligands can be done with

retention or with loss of the system's chirality.

Achiral metallocenes with a Cs-symmetry instead of a C2-symmetry have been described by W e n et al. 3 , as

syndiospecific catalysts. These are bridged fluorene-

cyclopentadienyl-systems. Chiral compounds of the fluo-

rene-cyclopentadienyl-type can be obtained by suitable

substituition. Seemingly trivial examples of achiral

bridged systems are the meso compounds of the bisin-

deny1 type.

The first example of our experiments is a Zr-com-

pound in which the dimethylsilylbridge of the reference

compound is substituted by a single carbon bridge (2 and table 1).

506 M. Antberg, V. Dolle, R. Klein. J. Rohrmann. W. Spaleck and A. Winter

The C2-symmetry of the reference compound is re-

tained but the bridge should be shorter, C-C-bonds

being shorter than Si-C-bonds. The activity of the com-

pound is lower than the reference compound, and molecu-

lar mass and isotacticity of the polymer are reduced

(table 1). The calculated average isotactic sequence

length is 11.5. Statistical analysis of the I3C-NMR

spectra of the polymers shows a site controlled chain

growth (characteristic triad compositions and triad

tests are listed in table 2 , the formulas used for cal-

culation are included 6 ) ) . I. e. along the chain two isotactic blocks are separated from one another by only

one propene unit with the opposite configuration of the

tertiary carbon atom. To distinguish this microstruc-

ture from those known in the art the term Ifisoblock"

polymer is proposed here.

table 2: triad / pentad compositions determined by 13C-NMR spectroscopy

corn- mmmm mmrm rmmr mmrr mmrm+ MM rrrr mrrr mrrm 2rr/mr pound or: nun rmrr or: rr

or: mr

71.42 13.6% 6.52 0.96 10 262 412 332 0.8 2.0

1

3.1 f

472 342 192 1.1 5.5

I 172 152 42 211 62 - 172 142 62 2.4

B 37.82 40.32 21.9 2 1.1 2.0

* 2rr/mr equals 1; if enantiomorphous site control ** (4 mm rr) / ( M ) ~ equals 1; if chain end control

35. Propylene pOlyme&ation ty Stm' ig id Metalloem Gztalysts 507

If one takes away one six ring from compound 1 a

chiral system is obtained which has no Cpymmetry (4 ) .

The experimental results of the polymerization

with this compound also demonstrate a loss of

stereospecifity (table 1 ) . In this case a completly

atactic polymer is obtained.

For better comparison with the reference compound

we also prepared an analogue of 4 with a dime-

thylsilylbridge (5).

Activity and molecular mass of the polymer are

comparable to 4 (table 1). 13C-NMR analysis of the po-

lymer reflects the results of bisindenyl compounds 2 and 2 on a lower level. Here again the structure with

the silicon bridge has a higher stereospecifity. The

microstructure of the chain is nisoblocklg, built under

site control.

508 M. Antberg, V. Dolle, R. Klein, J. Rohrmann, W. Spaleck and A. Winter

The first syndiospecific metallocene catalyst (a) has been published by Ewen et. al. 3).

The polymerization results of 6 are summarized in

table 1. We synthesized the compound according to

Ewen's procedure and tested it under polymerization

conditions as above. Using a mirror symmetrical type of

metallocene highly syndiotactic polypropylene is obtai-

ned. The activity is lower than that of the reference

compound. The molecular mass of polymer which is ob-

tained is comparingly high. The comparison of isotacti-

cities is not significant.

The Cs-symmetry of the syndiospecific system can

be easily disturbed by placing a methyl group on 3-PO-

sition of the cyclopentadienyl ring (2).

Thus the molecule becomes chiral, but the overall

effect of the symmetry disturbance on polymerization

behaviour is the same as in bisindenyl series: Sharp

35. Prwkne PolymeniariOn by Sterm'igid Metallocene Catalysts 509

reduction of the catalyst activity and stereospecifity

and a low molecular mass of the polymer. A more detai-

led study of the chain microstructure shows that

isotactic as well as syndiotactic sequences are contai-

ned in the polymer chain. Concerning the type of ste-

reochemical control no statement can be given. The iso-

tactic and syndiotactic sequence length is about 4

units for each case. The pentad intensities determined

by 13C-NMR spectroscopy are listed in table 2 . Such a

polymer microstructure was not reported until now. We

want to propose the term ttsyndio-isoblocktt polymer for

this new type of microstructure.

The last example is a pure meso compound of the

bisindenyl type. These compounds are expected to make

atactic polypropylene. The meso form of bisindenyl-

ethylene-hafnium-dichloride (4) could be isolated in a stereochemical purity of more than 98 %.

The polymerization activity and the molecular mass

of the polymer are low (table 1). A great surprise was

the result of the microstructure analysis: the polymer

exhibits an isotacticity of 56 % (in this example we

used a polymerization temperature of .60 OC). The iso-

tactic sequences exhibit an average length of three units . The triad intensities determined by 13C-NMR

spectroscopy and triad tests are listed in Table 2 . The

510 M. Antberg, V. Dolle. R. Klein. J. Rohrmann, W. Spaleck and A. Winter

most astonishing result is the fact that these isotac-

tic sequences are built at chiral centers under enan-

tiomorphous site control. This is a contradiction to

the fact that a meso compound is achiral by definition.

For explanation the forming of a chiral active center

comprised of the coordinated propene, the polymer-

chain, the active metallocene species and the

methylaluminoxane has to be assumed.

In fig. 4 the well known polypropylene micro-

structures and those we found in our experiments are

compared. In isotactic polypropylene nearly all terti-

ary carbon atoms have the same configuration. Typical

se-quence lengths are about 50 or more. Atactic poly-

propylene shows a completely statistical distribution

of the configuration of the tertiary C-atoms. The iso-

tactic sequence length is two.

I I l l I I I I I

I l l I I I I I I I

-+%%+A+ m 111111111111111111

I I I I I I I I I I I I I I I

a t a c t i c

ryndiairoblock

ryndiotrctic

a tore00 lack

100 t a c t i c

i sob lock

f i g . 4: polypropyienm microstructure

Stereoblock PP contains isotactic sequences, wher-

ein the tertiary C-atoms of two neighboured isotactic

blocks have the opposite Configuration. The

35. hpykne PolvmeriUrriOn by Stereorigid Metallocme Catalysts 511

stereospecific conjunction of two propene units is here

controlled by the end of the polymer chain. Isoblock PP

contains isotactic sequences too. But these sequences

are build under enantiomorphous site control. In the

syndioisoblock polymer syndiotactic and isotactic units

change with one another in a statistical manner. The

type of stereochemical control cannot be analysed under

these circumstances.

CONCLUSIONS

To summarize the result of our experiments one

can complete fig. 3, where the possible variations of

the metallocene structure have been imaged, by the

polymerization results (s. fig. 5).

By this it can be demonstrated in which way mo-

difi-cations of the molecular structure of the me-

tallocenes are reflected in the polymer microstructure:

Shortening of the bridge leads to a new micro-

structure : the I1isoblockn polypropylene.

With non C2-symmetrical chiral compounds

llisoblocklp is also obtained in one case; with a special

bridge the complete loss of stereospecifity was found.

The experiment with a chiral substituted fluorenyl

type compound produces also a new type of microstruc-

ture: the tpsyndio-isoblocklt polymer. The use of mesu

compounds leads to polymers of low isotacticity.

The influence of structure variation on Catalyst acti-

vity and molecular mass of polymer can be summarized in

this way: Disturbance of symmetry is detrimental to ca-

talyst activity and favourable for chain determination

reactions.

512 M. Antberg, V. Dolle, R. Klein. J. Rohrmann. W. Spaleck and A. Winter

possible structural modifications

bridge between cyclopentadienyl rings

shorter longer - ligand system

(chiral compounds)

retaining chirality

retaining C2 -symmetry

loosing C2 -symmetry

100s ing chirality

-v4lm4P

(mirror

retaining symmetry - ligand system symmetrical compounds)

modifying symmetry by substituition

M f U t L - r fig. 5: metallocene structure --- polypropylene microstructure

The conclusions to be made are:

1) C2-symmetry is necessary but not sufficient for high isospecifity.

2) Further conditions concerning special electronic

factors and steric arrangements must be met.

3 ) In propene polymerization with stereorigid metallo-

cenes activity and stereospecifity are directed by the

same factors.

ACKNOWLEDGEMENTS

We thank Dr. Gann for GPC-measurements and Dr.

Kluge for the 13C-NMR investigations.

LITERATURE

1) W. Kaminsky, K. Kfllper, H. H. Brintzinger, F. R. W.

P. Wild, Angew. Chem., (1985) 507

2) J. A. Ewen, L. Haspeslagh, J. L. Atwood, H. Zhang,

J. Am. Chem. SOC., (1987) 6255

3) J. A. Ewen, R. L. Jones, A. Razavi, J. Am. Chem.

SOC., Ilp (1988) 6255

4) P. Pino, P. Cioni, J. Wei, J. Am. Chem. SOC.,

5) W. A. Herrmann, E. Herdtweck, J. Rohrmann, W.

Spaleck, A. Winter, Ang. Chem., 1989 in press

6) A. Zambelli, P. Locatelli, A. Provasoli, D. F.

Ferro, Macromolecules, (1980) 267

(1987) 6189

514 M. Antberg, V. Dolle, R. Klein, J. Rohrmann. W. Spaleck and A. Winter

7) W. Spaleck, M. Antberg, V. Dolle, R. Klein, J. Rohr-

mann, A. Winter, New J. Chem., Special Issue: "New Per-

spectives in Organometallic Chemistry" (Proceedings of

EUCHEM Konigstein Conference 111), in press

Appendix A

PreDaration of~lsotxowlidene - - ( 9 flwrenvl - - 3 me thvlcv - Dentadienvl - zi 'rconium-dichloridel (2 )

6.9 g (41.6 mmol) fluorene were dissolved in 30 cm3 THF and 41.6 mmol of 2.5 m solution of n-butylli-

thium in n-hexane was added. After 15 min of stirring

this solution was given to a solution of 5.0 g (41.6 mmol) of 2.6.6-Trimethylfulvene in 30 cm3 THF and stir-

red over night. After addition of 40 cm3 of water the

reaction product was extracted with ether. The organic

phase was dried over MgS04. The product has been cry-

stallized at -35 OC. Yield: 5.8 g (49 % ) .

A solution of 3.79 g of the ligand in 40 cm of

THF was added to 17 cm3 (26.5 mmol) of a 1.6 m hexane solution of n-butyllithium at O°C. After stirring for 3 0 min at room-temperature the solvent was removed by

destillation. The red residue was washed with hexane. 3 . 1 g ZrC14 were suspended in 60 cm3 of CH2C12 and the

dilithiumsalt was added at a temperature of -78 OC. Af-

ter slowly warming up to room temperature the orange mixture was stirred for 2 hours. The mixture was filte-

red and the solution was crystallized at -35 OC. Yield:

3.2 g (45 % ) of complex 2 .

35. PmpVlene P o l ~ t i o n ty Sterm'gid Metalloem Catalysts 515

'H-NMR (100 MHz, CDC13): 7.1-8.2 (m, 8 aromatic HIS),

5.91, 5.55, 5.37 (3 x dd, 3 x 1 Cp), 2.38, 2.35 (2 x 5, 2 X 3, =C(CH3)2), 2.11 (S,3, CP-CH3)

Appendix B

a1 Polwrization P r o c e d u

A dry 16 dm3 reactor was flushed with nitrogen and

filled with 10 dm3 of liquid propene. Two third of the

methylaluminoxane / toluene-solution to be used was

then added and the reaction mixture was stirred at 30

OC for 15 minutes.

In a parallel procedure the metallocene to be

used was dissolved in one third of the MA0 quantity and preactivated by standing for 15 minutes. The solution

was then introduced into the reactor. The polymeriza-

tion system was brought to a temperature of 70 OC and

then kept for the desired time at this temperature.

The polymer was dried for 24 hours in vacuum at 70

OC. No further purification was carried out.


517

36. Polymerization of Styrene and Copolymerization of Styrene with Olefin in the Presence of Soluble Ziegler-Natta Catalysts

Masahiro Kakugo, Tatsuya Miyatake, Kooji Mizunuma

Chiba Research Laboratory, Sumitomo Chemical Co., Ltd., 2-1 Kitasode, Sodegaura-cho, Kimitu-gun, Chiba 299-02, Japan

ABSTRACT Titanium complex catalysts including 2,2'-thiobis(4-methyl-6-t-

butylphenoxy) (TBP) group as ligand are highly active toward styrene when combined with methylalumoxane (MAO) as cocatalyst, yielding completely syndiotactic polystyrene with up to 37 kg polymer per g titanium and hour. Copolymerizations of styrene and ethylene have

been carried out with these catalysts. The 13C NMR analysis of the copolymer obtained indicates that the copolymer is an alternating

copolymer having isotactic styrene units. The isotactic alternating copolymer is a crystalline polymer with a melting point of 116°C.

INTRODUCTION Syndiospecific catalyst systems €or styrene polymerization which

are composed of several titanium or zirconium compounds and

methylalumoxane (MAO) as a cocatalyst have been reported by several

authors (i.e., Ti(oR),,l~~) Zr(OR)4,1) TiC14,2) Cp2TiC12's2) (Cp=cyclopentadienyl) , CpTiClg , 2 , TiBz43-5) (Bz=benzyl) , or Z~(BZ)~.~-~) However, as far as we know, the copolymerization of styrene and olefin in the presence of these catalyst systems has not

yet been reported. Recently we developed catalyst systems, a combination of the Ti

complexes having 2,2'-thiobis(4-methy1-6- t-butyl-phenoxy) (TBP) group and MAO, which are specifically active toward styrene, giving syndiotactic polymer1) and also active toward olefins.6) In the

present work we found that these catalyst systems can copolymerize styrene with ethylene, giving highly alternating ethylene-styrene (ES) copolymer. This paper deals with the results of styrene

polymerization and ethylene-styrene copolymerization with TBP-Ti

complex (i.e., (TBP)TiC12 and (TBP)Ti(OPri)2) and Ti complex having

the corresponding methylene bridged ligand (i.e. , (MBP)Ti(OPri)2)) , and the molecular structure of the ES copolymer obtained.

EXPERIMENTAL Material s

Titanium tetrachloride and titanium tetraisopropoxide were purchased from Wako Pure Chemical Industries, Ltd.

Trimethylaluminum was purchased from Toyo Stauffer Chemical. 2,2'- Thiobis(4-methyl-6-t-butylphenol) (TBP) and 2,2'-methylenebis(4-

methyl-6-t-butylphenol) (MBP) were suplied by Ciba-Geigy AG. These materials were used without purification.

Syntheses of Ti complexes

TBP (0.84 mmol) was dissolved in butylether (50 ml) in a three- necked flask under nitrogen. Titanium tetraisopropoxide (0.84 mmol) was added by syringe to the solution with stirring at room temperature. The mixture was stirred at room temperature for 3 days, yielding a dark-brown solid. The dark-brown solid was

collected by filtration, washed with toluene (50 ml) three times, and dried in vacuo. (TBP)Ti(OPri)2 was obtained in a yield of 59.3%.

(TBP)TiC12 was obtained in a yield of 63.1% in a manner similar to that described above except for the use of titanium tetrachloride (0.84 mmol) instead of titanium tetraisopropoxide. (MBP)Ti(OPri)2

was obtained in a yield of 72.0% by the reaction of MBP (0.84 mmol)

and titanium tetraisopropoxide (0.84 mmol) in a similar manner.

Polymerization procedure Methylalumoxane (MAO) was prepared by the reaction of

trimethylaluminum with CuS04 5H20 according to the procedure reported previously. 7, Polymerization of styrene was carried out in toluene (20 ml) in an agitated 100 ml three-necked flask. Both t it anium

complex and MA0 were fed into the flask then stirred for 10 min at polymerization temperature before styrene (10 ml) was added. Polymerization was stopped by adding a mixture of methanol and

hydrochloric acid. The polymers obtained were washed with methanol, filtered, and dried in vacuo at 60°C for 4 h. The copolymerization

of ethylene and styrene was carried out in a 200 ml three-necked

36. Homo-and Co-polymerization of Slyrene with Okfin with Soluble Catalysis 519

flask in 40 ml of toluene. The catalysts were fed into the flask and the flask was heated to the prescribed temperature. After styrene was added, ethylene was introduced into the flask and fed so

as to keep the pressure constant during polymerization. The polymerization was terminated by adding 2-methylpropanol . The catalyst residues were removed by treating with 1N HC1. The product was recovered by adding the organic phase to a large excess

of methanol and dried in vacuo at 50°C for 4h. More detailed polymerization conditions are given in the footnotes to Tables 1, 2,

and 4 .

Analysis of polymers The molecular weight (Mw and Mn) and the molecular weight

distribution of the polymers were measured by gel permeation chromatography (Waters 150C) at 140 "C using o-dichlorobenzene as

solvent. The 13C NMR spectra of polymers were measured at 25.1 MHz

in a 9:l ratio of o-dichlorobenzene and benzene-dg (fieldlfrequency

lock material) at 135 "C or CDC13 at 30°C on a JEOL JNM-FX-100 spectrometer. Hexamethyldisiloxane (HMDS) was used as the internal reference (2.03 ppm vs tetramethylsilane). The nomenclature to designate the different types of carbons follows that suggested by

Carman and Wilkes. 8, Backbone methylene carbons are identified as S with two Greek letters indicating distance in both directions from the nearest tertiary carbon. Similarly, methine carbons are

identified as T with two Greek letters. The chemical shift was

calculated by using the method reported by Randall . g ) The calorimetric measurement was carried out on a Perkins Elmer DSC-2

differential scanning calorimeter.


STYRENE POLYMERIZATION Table 1 shows the results of polymerization with TBP-Ti complex-

MA0 systems, compared with the MBP-Ti complex-MA0 system, and the Ti(OPri)4-MA0 system. The 13C NMR spec t ra of all polymers obtained

showed that the structure of the polymers was highly syndiotactic.

520 M. &go, T. Miyatake and K. Mizunuma

Table 1. Polymerization of styrene with Ti complex-MA0 systemsa)

Run Ti complex Polymn. Activity 10-4-Mw Mw/Mn Syndio-

no. temp.("C) g/(mmolTi.h) tact ici ty

1 (TBP)Ti(OPri)2 60 2 80 3 100

4 (TBP)TiC12 60 80 100

5 (MBP)Ti(OPri)2 80 6 Ti(OPri)4b) 80

3 00 1780 840

690 2350 840

370 70

27.0 2.4 >98 7.8 2.8 >98 4.1 2.7 >98

19.0 2.3 >98 8.7 2.1 >98

4.1 2.7 >98

10.1 2.3 >98

8.1 2.4 >98

a) Other polymerization conditions: Ti complex, 0.003 mmol;

b, Ti(OPri)4, 0.018 mmol.

MAO, 6.8 mmol; Toluene, 20 ml; Styrene, 10 ml.

The catalytic activity of TBP complex systems was much higher than that of the Ti(OPri)4 system. The MBP-Ti catalyst also had

high activity, but somewhat inferior to the TBP-Ti catalysts,

suggesting that the bridging sulfur in the TBP ligand plays an important role enhancing catalytic activities. The electron donation of sulfur to titanium is anticipated to result in increase of activity. The maximum catalytic activity was obtained at the

polymerization temperature of 80°C in both TBP complex systems. The decrease in catalytic activity at above 80°C may be attributed to deactivation of the catalytic centers or exchange of the catalytic centers to less active centers.

The molecular weight of the polymers decreased with increase in

polymerization temperature. There was no significant difference in the molecular weight between the polymers prepared with the TBP complex systems and those prepared with the Ti(OPri)4 system.

Mw/Mn of the polymers increased slightly with increasing

polymerization temperature. The variation of the molecular weight distributions was attributable to the relative increase in the amount

36. Homo-and cO-polynreriurti0n of S&me with Olefin with Soluble Catalysb 521

of the polymer having lower molecular weight than that of the main

polymer. Some exchange of catalytic centers may occur at high polymerization temperature, resulting in broadening of the molecular

weight distribution.

COPOLYMERIZATION OF ETHYLENE AND STYRENE WITH VARIOUS

CATALYST SYSYTEMS

Table 2 shows the results of the copolymerization of ethylene and styrene with various Ti complex-MA0 systems. The catalytic

activities of (TBP)Ti(OPri)2 and (TBP)TiC12 were higher than

(MBP)Ti ( OPr i, 2 and Ti (OPr i, 4. This tendency was similar to that found in the case of styrene polymerization. There was no

significant difference in the molecular weight among the polymers obtained. The Mw/Mn of the polymers prepared with the TBP-Ti

complex was somewhat smaller than that prepared with the MBP-Ti complex and Ti(OPri)4 catalyst systems.

Table 2. Copolymerizations of ethylene and styrene with various catalyst systemsa)

Run Catalyst Activity 10-4.Mw Mw/Mn no. g/mmolTi.h

7 (TBP)Ti(OPri)2 9.4 2.0 2.1

8 (TBP)TiC12 4.8 1.9 1.9 9 (MBP)Ti(OPri)2 1.4 2.1 2.4

10 Ti ( OPri) 4 2.1 2.5 2.8

a) Polymerization conditions: Ti complex, 0.077 mmol; MAO, 34.5 mmol; Styrene, 4 ml; Ethylene, 0.3 atm; Toluene, 40 ml; Polymerization temperature, 80°C; Polymerization time, 2h.

Figure 1 shows the I3C NMR spectra of polymers obtained with these catalyst systems. The spectrum of the polymer obtained with the (TBP)TiC12 system (spectrum (A ) ) was very similar to that of the

522 M. Kakugo, T. Miyatake and K. Mizunuma

‘A) 146.6 145.6 phC1

i 146.6 145.6

(B) phC1

145.6

1 145.6

I

37.0 SarorSad

+ and DhC2-C6 i

37.0 * SarorSa 6

and phC2-C6

* and phC2-C6

41.6

SYb $66

* and C2-C6

41.6 45.0 TO6

1

100 50 0 150

ppm from TMS

Figure 1. 13C NMR spectra of ES copolymers prepared with various

catalyst systems: (A ) ; (TBP)Ti(OPri)2-MA0, (B); (TBP)TiC12

-MAO, (C); (MBP)TiClz-MAO, (D) ; Ti(OPri)h-MAO. * solvent peak (0-dichlorobenzene)

36. Homo-and Co-polymeriUrtimr ojS&ene with Olefin with Soluble Catalysts 523

polymer obtained with the (TBP)Ti(OPri)2 system (spectrum (B)). In spectra (A) and (B), the two peaks at 146.6 and 145.6 ppm in the aromatic carbon region are assigned to phenyl C-1 carbons in styrene units. The peaks attributed to the other phenyl carbons

overlapped those attributed to phenyl carbons in o-dichlorobenzene used as a solvent. The three main peaks at 46.0, 37.0, and 25.7

ppm in the aliphatic carbon region can be assigned to Tbb, Sar or Sob,

and Sob in copolymer sequence according to the improved Grant and Paul empirical method through calculated chemical shifts, 9, as shown in Table 3 .

Table 3 . Calculated and observed chemical shifts

Carbon type Sequence Chemical shift ppm from TMS Calc. Obs.

T bb ESE 45.9 46.0 Savor Sob SEE or SES 37.1 37.0

Sbb SES 25.9 25.7

On the other hand, only three signals could be found in this

region of the spectra of the polymers prepared with (MBP)Ti(OPri)2 and Ti(OPri)4 systems (spectra (C) and (D)). The three peaks in the

aliphatic carbon region are assigned to Saa and T&3 in syndiotactic styrene sequence (45.0 and 41.6 ppm, respectively) and Srb and Sbb in ethylene sequence (30.0 ppm). The peak at 145.6 ppm is also

assigned to the phenyl C-1 carbon in syndiotactic polystyrene. These

findings indicate that these catalyst systems produced syndiotactic polystyrene and polyhthylene under the same conditions with TBP-Ti system. This suggests that the ligand having a sulfur atom as the bridging group may contribute to the production of ES copolymer.

COPOLYMERIZATION OF ETHYLENE AND STYRENE UNDER VARIOUS POLYMERIZATION CONDITIONS Table 4 shows the results of the copolymerization of ethylene

and styrene under different styrene feed concentrations with the (TBP ) Ti ( OPr ) 2 -MA0 s y s t em. The catalytic activity as well as the

Mw and Mw/Mn increased with increasing styrene concentration.


(A)

146.6

146.6 phC1

L

and phC2-C6

46.0

4 30.0

Sva , S d d 27.8

I, 37.0

SavorSoa

25.7 sol3

L 41.6

150 100 50 ppm from TMS I

Figure 2. 13C NMR spectra of ES copolymer obtained under different

styrene concentration.

Feed styrene: ( A ) ; 1 ml, (B); 2.5 ml, (C); 6.0 ml. * solvent peak (0-dichlorobenzene)

36. Homo-and CO-polymerization of Slyrme with Okfin with Solubk Gafalysts 525

The 13C NMR spectra of the copolymers obtained are shown in

Figure 2. In all spectra three peaks at 46.0, 37.0, and 25.7 ppm attributed to the carbons in ES copolymer could be observed. In the spectrum of the copolymer obtained under low styrene concentration (spectrum (A)), two peaks at 30.0 and 27.8 ppm were observed in

Table 4. Copolymerizations of ethylene and styrene with

the (TBP)Ti(OPri)2 and MA0 systema)

Run Styrene Ethylene Activity 10-4-Mw Mw/Mn

no. ml atm g/mmolTi. h

11 1.0 0.3 5.5 0.7 1.5 12 2.5 0.3 6.5 1.3 1.9 13 6.0 0.3 9.4 2.0 2.1

a) Polymerization conditions: T i complex, 0.077 mmol; MAO, 34.5 mmol; Toluene, 40 ml; Polymerization temperature, 80°C; Polymerization time, 2h.

addition to the three peaks. The peak at 30.0 ppm has been

assigned to Sy6 and Sacarbons, and the peak at 27.8 ppm to St96 carbon by Soga et a1.l0) in ES copolymer having isolated styrene units in the sequence. On the other hand, in the spectrum of the copolymer obtained under high styrene concentration (spectrum (D)), three additional peaks at 45.0, 43.8, and 41.6 ppm were observed.

The peak at 45.0 ppm was assigned to the T&3 carbon and the peak at 41.6 ppm to the Saa carbon in syndiotactic polystyrene as described

above. The peak at 43.8 ppm can be assigned to the T&9 carbon according to che improved Grant and Paul empirical method9) (calc.

43.9 ppm). In order to characterize the molecular structure of the ES

copolymer in detail, we prepared much higher quantities of copolymer under conditions similar to those of Run no. 12.

THE MOLECULAR STRUCTURE OF ES COPOLYMER 2.4 g of the ES copolymer was obtained by scaling up five times.

The Mw and Mw/Mn of the copolymer were 13000 and 1.9, respectively.


The polymer was extracted with THF. The percentage of the polymer

extracted was 80%. THF soluble fraction (THF-Sol.) and THF insoluble fraction (THF-Insol. ) were characterized by I3C NMR. The

13C NMR spectra of the original polymer, THF-Sol. and THF-Insol. are shown in Figure 3 . In the NMR spectrum (B) of the THF-Sol., the

three resonances attributed to T66, Say or S o b , and SgB carbons were observed with a peak intensity ratio of 3. 1:2:1. This indicates

clearly that styrene units and ethylene units are incorporated

alternately in the polymer sequence:

Ph Ph Ph Ph

I I I I c - c - c - c - c - c - c - c - c - c - c - c - c - c ~ - c - (I)

Say SBB Say Tbb

From these findings, the peak at 146.6 ppm can be assigned to the phenyl C-1 carbon attached to the Tbb carbon.

On the other hand, the spectrum of the THF-insol. (spectrum (C)

of Figure 3 ) was quite different from that of the THF-sol. The peaks at 145.6, 45.0, and 41.6 ppm were coincident with those of

syndiotactic polystyrene. These findings indicate that the copolymer obtained is a mixture of ES alternating copolymer and syndiotactic polystyrene, suggesting that the active center producing ES alternating copolymer is different from that producing syndiotactic polystyrene.

ES alternating copolymer was first synthesized by Suzuki et

a1 .I1) by hydrogenating 1,4-poly(l-phenylbutadiene) or 1,4-poly(2- phenylbutadiene). Figure 4 shows the I 3 C NMR spectra of these ES

alternating copolymers reported by them. In both spectra, four resonances attributed to phenyl C1, Tbb , Say , and SOB carbons were

further split, i.e., phenyl C1; triplet, Tbb ; triplet, S a y ; quartet, and Sgg ; doublet. They have interpreted these splits as differences in configurational arrangements of phenyl groups and have

concluded that the ES alternating copolymers thus obtained are atactic.

In spectrum (B) of Figure 3 , there is no splitting of the peaks of phenyl C1, Tbb , Say , and S&3 carbons. The chemical shifts of these peaks are summarized in Table 5, compared with those reported

36. Homo-and CO-polymerization of S@rene with Olefin with Soluble COtabstS 527

37.0 say

41.6 * and phC2-C6

0 ppm from TMS '

150 100

Figure 3. 13C NMR Spectra of ES copolymer:

( A ) ; original copolymer, (B); THF-soluble fraction,

(C); THF-insoluble fraction.

solvent peak (0-dichlorobenzene) 9:

528 M. Kakugo. T. Miyatake and K. Mizunuma

by Suzuki et a1.l1)

copolymer are completely coincident with those of the m diad or mm

triad sequence. From these results, we have concluded that the

present ES alternating copolymer is isotactic. Thermal analysis using DSC showed the melting point of the copolymer to be 116°C.

The chemical shifts of the present ES

Figure 4. 13C NMR spectra of the ES copolymers obtained by the hydrogenation of (A ) 1,4-poly(2-phenylbutadiene) and (B) lJ4-poly(l-phenyl butadiene)ll). (Macromolecules, 13 , 849 (1980))

REFERENCES

1. M. Kakugo, T. Miyatake, and K. Mizunuma, Chemistry Express, 2 ,

2. N. Ishihara, M. Kuramoto, and M. Uoi, Macromolecules, 21, 3356 445 (1987).

(1988).

36. Homo-and Co-po lyme~t ion of SIyrene with Okfin with Solubk #ta&sfs 529

Table 5. 13C NMR assignments of the alternating ES copolymer

~ ~ _ _ _ _ _ _ ~~

Carbon type Tacticity Chemical shifts in ppm from TMSa)

ref. 8 our data

phenyl C1 mm mr

rr T rr

mr mm

S rr rm

mr mm

S r m

146.2 146.2 146.1 146.0 45.6 45.5 45.4 45.4 37.0 36.9 36.7 36.6 36.6 25.4 25.2 25.2

~ ~~~

a) The I3C NMR spectra were measured in CDC13.

3. C. Pellecchia, P. Longo, A. Grassi, P. Ammendola,and A. Zambelli,

4. A . Zambelli, P. Longo, C. Pellecchia, and A. Grassi,

5. A . Grassi, P. Longo, A. Proto, and A. Zambelli, Macromolecules,

6. T. Miyatake, K. Mizunuma, and M. Kakugo, Makromol. Chem.,

7. H. Sinn, W. Kaminsky, H.-J. Vollmer, and R. Woldt, Angew. Chem.,

8. C. J. Carman and C. E. Wilkes, Rubber Chem. Technol., 44, 781

9. J.C. Randall, J. Polymer Sci., Polymer Phys. Ed., 13, 901 (1975).

Makromol. Chem., Rapid Commun., 8 , 277 (1987).

Macromolecules, 20 , 2035 (1987).

2 2 , 104 (1988).

Rapid Commun., 10, 349 (1989).

9 2 , 396 (1980).

(1971).

10. K. Soga, D.-H. Lee, and H. Yanagihara, Polymer Bulletin, 20 ,

11. T. Suzuki, Y. Tsuji, Y. Watanabe, and Y. Takegami, 237 (1989).

Macromolecules, 13, 849 (1980).


531

37. Propylene Polymerizations with Silylene-Bridged Metall- ocene Catalysts

* Shinya Miya, Takaya Mise*, H i r o s h i Yamazaki

Chisso Petrochemical Corporation,

5-1 Goikaigan, I c h i hara-shi, Chiba, 290, Japan

The I n s t i t u t e o f Phys ica l and Chemical Research (RIKEN),

Wako-shi, Saitama, 351-01, Japan

*

Abstract

New C2-symmet r ic s i l y l e n e - b r i d g e d metal locene compounds, [Me2Si(Rn-

C5H4-.,)( R'm-C5H4-m ) ] M C l z ( M = Z r , H f ; Rn, R',=Me, t-Bu, 2,4-Me2, 2,3,5-Me3),

were synthesized together w i th C1-symmetric compounds (M=Zr,Hf; Rn=2,3,5-

Me3, 2.4-Me2, 3.4-Me2, t-Bu, Me; R',=Me,H) f o r comparison and employed as

the c a t a l y s t s f o r i s o t a c t i c po l ymer i za t i on o f propylene i n combina t ion w i t h

methylaluminoxane. The C2-symmetric meta l locenes bear ing methy l groups a t

t he 2- o r 5 -pos i t ions gave polymers of t h e h ighes t m e l t i n g p o i n t (160-163

'C) and s te reo regu la r i t y ([mmmm]=97-99%).

Introduction

Homogeneous m e t a l locene/a luminoxane c a t a l y s t s have h igh performance

f o r producing a tac t i c , i s o t a c t i c , and s y n d i o t a c t i c polypropylene') having

n a r r o w m o l e c u l a r w e i g h t d i s t r i b u t i o n , and t h e y p r o v i d e good mode ls f o r

s t u d y i n g t h e r e l a t i o n s h i p be tween t h e l i g a n d s t r u c t u r e and t h e p h y s i c a l

p r o p e r t i e s o f polypropylene.

P r e v i o u s l y we r e p o r t e d t h e p r e p a r a t i o n o f a l l members o f z i r c o n i u m

compounds o f (Men-C5H5-n)2ZrC12 and t h e i r use i n propylene po lymer iza t ions .

The number and t h e p o s i t i o n o f methyl groups on cyclopentadienyl(Cp) r i n g s

were c o n f i r m e d t o e x e r t g r e a t i n f l u e n c e on t h e p h y s i c a l p r o p e r t i e s of

a t a c t i c polypropylene.')

Ethylene-bridged indeny l o r t e t rahyd ro indeny l mo ie ty i s a w e l l known

l i g a n d o f m e t a l l o c e n e c a t a l y s t s i n t h e p r o d u c t i o n o f i s o t a c t i c

532 S. Miya, T. Mise and H. Yamazaki

po1ypropylene.l) However, a major l i m i t a t i o n o f these zirconocene c a t a l y s t s

i s t h a t t h e y o n l y produce l o w m o l e c u l a r w e i g h t and l o w m e l t i n g p o i n t

polymers. I n o r d e r t o improve t h i s , we p r e s e n t he re t h e s y n t h e s i s o f new

s i ly lene-br idged metallocenes and t h e i r use i n i s o t a c t i c polymerizat ion.

Experimental

Chi r a l s i 1 y l ene-br i dged meta l locenes o f IMe2Si ( Rn-C5H4-n)( R1,,,-C5H4+,

)]MC12(M=Zr,Hf; Rn,Rtm=Me, t-Bu, 2,4-Me2, 2,3,5-Me3) have been synthesized

( 1 a - l ~ ) ~ ) i n a f o u r - s t e p procedure, as shown i n Scheme 1. C p y m m e t r i c

metallocenes ( l a - l d and 11-10) were prepared as t h e racemic ( d l ) mix tures

w i t h t h e co r respond ing meso isomers. The d l - e n r i c h e d C2-symmetr ic

m e t a l l o c e n e s o b t a i n e d b y r e c r y s t a l l i z a t i o n and t h e C 1 - s y m m e t r i c

m e t a l l ocenes were used f o r propylene polymerizat ion.

[M]=2x1 0-6 mol , A 1 /M( rnol a r r a t i o ) = IO,OOO(M=Zr,Hf), Temp.:30°C, Time:Ehr,

C3':3kg/cm2G, Solvent : Toluene(500ml). P o l y m e r i z a t i o n was s topped w i t h

a c i d i f i e d methanol.

P o l y m e r i z a t i o n was c a r r i e d o u t under t h e f o l l o w i n g c o n d i t i o n s :

Results and Discussion

The p h y s i c a l p r o p e r t i e s o f t h e p o l y p r o p y l e n e o b t a i n e d by t h e s e

ca ta l ys ts are l i s t e d i n Table 1. It was found t h a t a l l c h i r a l metallocene

ca ta l ys ts produced i s o t a c t i c polypropylene and t h e number, pos i t ion, and

k i n d o f subst i tuents on the Cp r i n g s exerted g r e a t i n f l uence on c a t a l y t i c

a c t i v i t y and on phys ica l p roper t i es o f t h e polypropylene. The C2-symmetric

metal locenes produced polymers o f h igher molecular weights, m e l t i n g points,

37. Propylene PolymerLations with Silylene-Bridged Metalloaene Gztalysts 533

and t a c t i c i t i e s t h a n C1-symmet r ic metal locenes. Among t h e C2-symmetric

ca ta l ys ts , metal locenes bear ing methyl groups a t t h e 2- o r 5 -pos i t ions ( la,

l b , 11 and l m ) gave t h e b e s t r e s u l t s . When b u l k y s u b s t i t u e n t s were

in t roduced a t t he 3-pos i t ions i n t h e C2-symmetric ca ta l ys ts , cons iderab le

decrease o f a c t i v i t y was observed.

Wi th hafnocene ca ta l ys ts , h igher mo lecu la r we igh t and s l i g h t l y more

s t e r e o r e g u l a r p o l y m e r s were produced compared t o t h o s e p roduced w i t h

zirconocene ca ta l ys ts , a l though t h e c a t a l y t i c a c t i v i t y was ve ry low.

Table 1. Resu l ts o f propylene po lymer i za t i on

Ca ta l ys ta Rn R ' m A c t i v i t y 6 G/G m.p. [m]

[dl/meso r a t i o ] ('C) (XI

(M=Zr)

l a [85/15] 2,3,5-Me3 2',4',5'-Me3 1.59

l b [94/ 61 2.4-Me2 3',5'-Me2 11.1

I d [88/12] 3-Me 4'-Me 16.3

l e [90/10Ib 2,4-Me2 3 ' -o r 4'-Me 2.54

I f 3.4-Me2 3'-Me 1.94

l g 3-t-Bu 3 ' -o r 4'-Me 5.91

l c [73/27] 3-t-BU 4'-t-8u 0.31

l h 2,3,5-Me3 H 7.35

li 2, 4-Me2 H 5.23

1 j 3-t-BU H 7.94

lk 3-Me H 6.69

133900

86500

9560

13700

18700

5050

6370

15500

10600

4260

6610

1.99

1.93

2.32

2.25

2.06

2.38

2.61

2.27

2.33

2.13

2.19

162.0

160.4

149.4

147.8

154.5

133.0

146.0

85.1

68.9

125.7

79.5

97.7

97.1

93.4

92.5 - -

89.4

49.9

41 .O 77.9

52.4

(M=Hf)

11 [93/ 71 2,3,5-Me3 2',4',5'-Me3 0.30 256100 2.38 162.8 98.7

lm [ l o o / 01 2,4-Me2 3',5'-Me2 0.14 139200 1.84 162.4 98.5

10 [52/48] 3-Me 4'-Me 1.61 66800 3.53 148.2 - I n [26/74] 3-t-BU 4'-t-BU 0.03 17190 2.84 157.4 -

1P 3-Me H 0.06 52800 2.59 103.8 -

a)dl-Enriched meta l locenes obtained by r e c r y s t a l l i z a t i o n (except I n and l o )

were used. b)Isomer r a t i o o f 3'-Me and 4'-Me isomers.

534 S. Miya, T. Mise and H. Yamazaki

Under comparable po l ymer i za t i on cond i t ions , l a and l b gave polymers o f

h i g h e r m o l e c u l a r w e i g h t and more s t e r e o r e g u l a r i t y t h a n t h o s e w i t h

Et(Ind)2ZrC12 and t h e same i s t r u e f o r 11 and l m versus Et(1nd)2HfClE. Th is

s u p e r i o r i t y o f dimethylsilylene-bridged meta l locenes over ethylene-br idged

ones may a r i s e f rom t h e h ighe r s t e r e o r i g i d i t y o f t h e fo rmer connect ing two

Cp r i n g s w i t h o n l y one atom.

References

1) W.Kami ns ky, K.K'irlper, H.H.Brintzi nger, F. R. W.P.W i I d , Angew.Chem. I nt . Ed.

Engl., 24, 507(1985): J.A.Ewen, L.Haspeslagh, J.L.Atwood, H.Zhang, J.Am.

Chem.Soc., 109, 6544(1987): J.A.Ewen, R.L.Jones, A.Razavi, J.D.Ferrara,

J.Am.Chem.Soc., 110, 6255(1988) and re fe rences c i t e d there in .

2) S.Miya, M.Harada, T.Mise, H.Yamazaki, P o l y m e r P r e p r i n t s , Japan, 36,

No.2, 189(1987): T.Mise, K.Aoki, H.Yamazaki, S.Miya, H.Harada, 3 4 t h

Symposium on Organometal l i c Chemistry, Japan, PA109, November, 1987.

3) P a r t o f t h i s work has been r e p o r t e d : H.Yamazaki, T.Mise, S.Miya, 6 t h

I n t e r n a t i o n a l Symposium on Homogeneous C a t a l y s i s , Canada, P-63, August,

1988; S.Miya, T.Yoshimura, T.Mise, H.Yamazaki, P o l y m e r P r e p r i n t s , Japan

( E n g l i s h E d i t i o n ) , 37, E13(1988).

535

38. Homogeneous Ziegler -Natta Catalysts and Synthesis of Anisotactic and ThermopIastic Elastomeric Poly (prop ylenes)

Dedicated to Professor T. Keii on the Occasion of his seventieth

birthday.

James.C.W. Chien*, Bernhard Rieger , Ryuichi Sugimoto, Daniel T. Mallin and Marvin D. Rausch

Department of Polymer Science and Engineering, Department of Chemistry

University of Massachusetts

Amherst, Massachusetts 01 003, U.S.A.

Anisotactic polypropylenes had been obtained with racemic ethylenebis-

(indenyl) zirconium dichloride (l)/methyl aluminoxane (MAO) and

ethylene-bis-(tetrahydroindenyl) zirconium dichloride (2)/MAO cata-

lysts from -55'C to 80'C and Al/Zr ratios between 80 to lo5. The

overall activation energy for polymerization is 10.6 kcal. mol.-'

This is, however, accompanied by a reduction of stereochemical control

as reflected by the formation of more polypropylene (PP) soluble in

low boiling solvent. At elevated temperature of polymerization (Tp)

no PP was obtained which is insoluble in refluxing n-heptane. Tritium

radiolabeling showed that at [All/[Zrl 2 3500 and 3OoC, two-thirds of 2 becomes catalytically active. There are two kinds of active species

formed in about equal amounts; one has more stereoselectivity, 10-20

times greater rate constant of propagation, and a factor of 5 to 1 5

faster chain transfer to M A 0 than the second kind of nonstereo-

selective catalytic species. This is also true at low [Al]/[Zr] of

350, except that the total amount of the two active species corre-

sponds to only 13 % of [ 2 ] . Replacement of MA0 with trimethyl

aluminum resulted in a decrease of stereoselectivity and loss of

catalytic activity proportional to the amount of replacement. As Tp

increases, the polypropylenes produced have progressively lower

melting transition temperature and homosteric sequence distribution,

and higher solubility. The polymers were fractionated by solvent

extraction. Most fractions have relatively high crystallinity (50%)

536 J. C. W. Chien, B. Rieger, R. Sugimoto, D. T. Mallin and M. D. Rausch

with a preference toward a thermally stable y -modification. The 3C-

NMR spectra showed single steric inversion to be the predominant

insertion error. The homosteric pentad distribution is neither that

expected for chain-end or enantiomorphic site stereochemical control

model. The microstructure of polypropylene can provide both a record

of stereochemical control and a measure of fluxional behavior of the

new homogeneous catalysts. The change in stereochemical control

during the course of propagation of a polypropylene chain was

demonstrated by the synthesis of homopolymers having twenty of more

alternating crystallizable and noncrystallizable segments exhibiting

thermoplastic elastomeric properties.

INTRODUCTION

Ziegler-Natta (ZN) catalysis is in a renaissance with vigorous

activities and advances achieved in both heterogeneous and homogeneous

systems. With regard to heterogeneous systems, the classical 6-TiCl3*

0.33A1C13/A1Et2C1 catalyst has only a minute fraction of the Ti ions

situated in certain kinds of surface sites being active for isospeci-

fic polymerization of propylene. The new MgC12 supported TiC13 cata-

lysts’t2) have hundred-fold more active sites per mol of Ti3) ([C*l)

each C* having ten-times faster rate constant of propagation (kp),

which in the presence of electron donating promoters4) produces poly-

propylene (PP) having macroisotacticity index ( 1 . Y . ) of 99% as

compared to 92% by the 6-TiC13 catalyst. Here, I.Y. is the percent of

refluxing n-heptane insoluble fraction which has maximum melting

transition Tm>16S0C and crystallizes in the a-modification. I .Y. is

the meaningful and practical measure in commercial production of that

polypropylene which possesses the broad set of useful properties.

independently

discovered the Cp2TiC12/A1R2C1 (Cp= q5=cyclopentadienyl) as the first

homogeneous ZN catalyst. Long and Breslow‘) had investigated the

mechanism and Chien7) had determined the absolute rate constants of

initiation, propagation and termination for ethylene polymerization

initiated by this catalyst. The active tetravalent Ti complex decays

rapidly by reductive elimination of polymer chain^.^) The catalyst produces only 1.2 x 1 04g polyethylene/(mol-Ti.hr.atm) and does not

polymerize propylene. Small amounts of impurities such as oxygen,

ether, and even moisture had beneficial effects on the polymerization

as long as their amounts are less than that of Cp~TiC12- Reichert and

Breslow and NewburgSa) and Natta et al.5b’

38. Synthesis of Anisatactk and R h c t m k Polvbroprlene 537

Meyer’) showed that the polymerization has an induction period if the

system is completely free of moisture. Addition of water reduced the

length of induction period and increased the rate of polymerization

(Re 1. Subsequently , Sinn , Kam insky and coworkers used ol igomer ic

methylaluminoxane (MAO) , which is the reaction product of trimethyl aluminum (TMA) and water, with group IV metallocene compounds to

obtain ethylene polymerization catalysts having extremely high

activities. For instance Cp2TiC12 /MA0 has a polyethylene productivity

of 9.3 x 106g PE/(mol-Ti’hr’atm) at 2OoC; the productivity is 9 x 107g

PE/(mol-Zr.hr.atm) at 7 O o C with Cp2ZrC12/MA0. But these catalysts

yielded only atactic polypr~pylenes.~~,~~~ The same is true for the

meso-Et[IndI2ZrCl2/MAO (Et[Ind12 = ethylenebis(indeny1)) and meso-

Et[ IndI2TiCl2/MAO’ 3, systems.

synthesized rac-ethylene bis(tetra-

hydroindenyl) and rac-ethylenebis(indenyl)(Et[1ndl2) ligands and the

dichlorozirconium compounds with these ansa-ligands Et[IndI2ZrCl2 ( 1 )

and Et [ IndH4 ] 2ZrC12 (2). Kaminsky and coworkers’ 2 , and Ewen’ 3, showed

that 1 and 2 activated with MA0 catalyzed stereoselective polymeriza-

tion of propylene. This finding demonstrated stereochemical control by

the chiral ansa-indenyl ligands on the transition metal ion in the

selection of one of the two enantiotopic faces (Re or Sill4) of a

prochiral vinyl monomer in migratory insertion. Other new stereoselec-

tive catalyst systems have been found: propylidene(cyclopentadienyl-1-

f luorenyl) hafnium dichloride/MAO’ 5, for syndiospecif ic propylene

polymerization and tetrabenzyl titanium/MAO’ 6, for syndiospecif ic

styrene polymerization. These developments have attracted many organo-

metallic and stereochemists to participate in this research area.

Brintzinger and coworkers’ ’

STEREOSELECTIVITY

No ZN-catalyst is completely stereospecific. The best hetero-

geneous ZN-catalyst produces polypropylene which contain conf igura-

tional defects ( 2 % to 5 % racemic diads17)). The stereoselectivity is

sufficiently high so that 99+% of the PP are insoluble in refluxing n-

heptane and have T, (melting temperature),l65OC. Such products are

commercially referred to as isotactic PP (i-PP).

It was a remarkable claim by Kaminsky et a112a,b) that at Tp = -

10 to +2OoC, the catalyst 2/MAO produced 99+% i-PP; less than 1 % of

the polymer was soluble in toluene (conditions unspecified). Subse-

quently, Soga et al,18) obtained polypropylene with the S-enantiomer

538 J. C. W. Chien. B. Rieger, R. Sugimoto, D. T. Mallin and M. D. Rausch

of 2/MAO at -lO°C, and extracted the polymer with boiling n-heptane.

The insoluble material (amount not given) has Tm = 160°C and [mml =

0.986; the soluble portion (amount also not given) has Tm = 149OC and

[ mm] = 0.961. The 3C-NMR spectra contained tetramethylene sequence

which was attributed to hydrogen-transfer l13-insertion. Grassie et

a,.”) found the stereoregularity of the PP obtained with 2/MAO

depended on the temperature of polymerization; the mmmm pentad

sequence decreased from 0.95 to 0.75 for polymers obtained at O°C and

25OC, respectively. There were also significant amounts of 1,3-inser-

tions and head to head enchainment. Ewen’) reported that the PP

obtained with rac-Et[IndH4I2TiCl2 at O°C has methyl pentads fractions

of [mmmm] = 0.56 and [rrrrl = 0.006, 86% m placements, and very low Tm

of 99OC.

We have polymerized propylene with I/MAO from -55’G to +8OoC.

Table 1 gave activity of the catalyst and the Tm of the polymer. The

DSC melting curves are very broad. There is a gradual decrease of Tm

P’ with Tp up to 2OoC then Tm drops rapidly with further increase of T

The polymer obtained in 8OoC polymerization displays a secondary

maxima in the melting endotherm (Fig. 1).

The intrinsic viscosities of the total polymers were determined

and given in Table 2. Their GPC curves showed steady increase of MW

and narrowing of distribution as Tp decreases. The values of Mn, Hw and MWD = RW/Wn are summarized in Table 2. Weight-average MW was

determined by light scattering for

Table 1 Propylene polymerizations

by Et [ Ind I22rCl2/MAO

TE A x 10-3 Tm -

“c kg PP/ [ Zr] [monomer] hr “c

80 -7.8 104

70 7.67, 7.16, 7.91 107

50 4.25, 4.1 128

30 2.31 , 2.0 136

20 1.16 138

0 0.14, 0.15, 0.16 143

-20 0.03, 0.026, 0.037 147

-55 0.02 , 0.0027 152

two polypropylene samples. The Mw

t lfM 103,6

Figure 1 DSC of total polymer at ZO’C/min

heating rate. second scan after complete melting

and cooling for polymer obtained at Tp - 80°C

38. S'thesis of Anisotoctic and Elastometic Polypn@vkw 539

thus obtained agree within 3%. The 90- results (Table 2) agree with the GPC

results within 6%. The two PP samples

have R, values of 440 A and 344 as

expected for its MW1 l2 dependence.

polymers were determined by 3C-NMR.

% ' 70 - z.

The microstructures of the total 5

Table 3 summarizes the steric diad, = a . triad and pentad distributions of

polymers obtained at different Tp. The 4]

population of mn sequences, (n = 1, 2,

4) all increase with the decrease of

Tp. Fig. 2 shows only gradual change of

m m m m fractions from 0.86 to 0.81

4l-

A

L I I b

Tp = 80'C. sequence distribution fraction with

polymerization temperatures.

Table 2 Molecular weight data for total polymers obtained with the

Et[IndI2ZrCl2/MAO system at different temperatures

GPC Light Scattering

80 -0.1 0.86 2.32 2.69

70 0.15 1.20 2.79 2.34

50 0.20 1.57 4.27 2.34

30 3.56 7.09 2.11

20 0.58 4.76 9.44 1.98 1 0 . 5 344 8.86

0.74 8.96 11.6 1.30 10.1 440 12.3 0

-20 0.92 9.35 14.2 1.52

HETEROGENEITY OF MICROSTRUCTURES

Even though the PP samples have reasonably narrow MW

distributions of FIw/Rn < 2.7 (Table 21, they are very heterogeneous in

microstructures according to solvent fractionation.20) The amount of

Table 3 Comparison of observed and calculat,ed steric sequence distributions

for total polymers

Pentad

FlEElll T Paranetere Triad

OC b Y Hodel' 11111 APD,tb m a -K ~~IIE APD,*

00 - - Ob 0.61 0.24 0.15 0.41 0.16 0.046 0.11 0.006 0.04 0.037 0.04 0.074

E'

0.037 - E 0.65 0.23 0.12 11 0 .41 0.15 0.013 0.15 0.054 0.03 0.013 0.01 0.076 39

70 - - Ob 0.73 0.16 0.11 0.57 0.14 0.02 0.10 0.034 0.021 0.010 0.023 0.073

0.894 - E 0.72 0.19 0.10 9 0.57 0.13 0.01 0.14 0.036 0.010 0.009 0.017 0.060 26

50 - - Ob 0.91 0.053 0.035 0.01 0.079 0.025 0.041 0.009 0.003 0.006 0.001 0.020

0.959 - E 0.00 0.079 0.039 18 0.81 0.069 0.002 0.069 0.006 0.003 0.002 0.003 0.035 56

0.97 0.005 E/C 0.91 0.06 0.03 9 0.85 0.053 0.001 0.053 0.004 0.002 0.001 0.002 0.009 76

0 - - Ob 0.91 0.061 0.024 0.03 0.054 0.027 0.034 0.013 0.014 0.006 0.007 0.014

0.964 - E 0.90 0.069 0.035 17 0.83 0.062 0.001 0.062 0.005 0.002 0.001 0.002 0.031 103

0.90 0.04 E/C 0.91 0.058 0.029 0 0.87 0.04 0.003 0.04 0.011 0.006 0.003 0.006 0.02 45

pl p m p P

P 3

F P P !2 B

aHodels are E(enantiomorphic - site control) and E/C (C-chain-end control), distributions calculated using equations of ewer^"^ and Doi et al,*5 respectively. from mean value.

Ob is the experimentally found distribution. bAverage of percentage deviation

38. Synthesis of Anisotnctic and EbstonreriC Polypmpvlene 541

polymer soluble in different solvents up to n-heptane and the amount

of insoluble polymers are summarized in Table 4. There is no C7 insoluble products in 7 0 ° C and 8 0 ° C polymerizations, or I.Y. = 0 in

these cases. In fact, all the polymers produced in these experiments

were soluble in c 6 . The polymers obtained at Tp = 5OoC has I.Y. =

17.5%. Even in the - 5 5 ° C polymerization, the I.Y. of the product is

only 86.2%. Most of the polymer fractions extracted with acetone or ether were brittle waxy substances characteristic for low melting and

low Xc ( = percent crystallinity) polymers.

Because of the large number of samples involved, they are

designated with T followed by the solvent it is soluble to facilitate

identification. For instance, the sample 2 0 " / E refers to the ether P

Table 4 Fractionation of anisotactic polypropylenes by solvent

extraction

Weight % of polymer soluble in Weight % of refluxing E T

O C Acetone Ether Pentane Hexane Heptane heptane insoluble

80 22 .5 3 4 . 8 1 7 . 5 25 .2 0 0 70 1 6 . 4 32.0 1 5 . 3 36.3 0 0 5 0 6 . 5 13 .6 2.4 46.4 1 3 . 6 1 7 . 5 20 2.4 4.7 2 . 8 2.6 1 2 . 9 74 .6

0 2.1 4 .3 2.4 2.9 1 3 . 9 7 4 . 4 -20 1 .a 4.2 2 .2 3.0 1 3 . 5 7 5 . 3 -55 0.2 0.9 0 .4 3.1 9.2 8 6 . 2

Table 5 Melting transition for anisotactic polypropylene fractions

Tm, OC Fraction soluble in c 7 ,i Total

OC Acetone Ether Pentane Hexane Heptane fraction polymer

1 0 7 70 54 8 6 1 0 5 1 1 3 50 wax wax wax 1 2 4 1 3 0 1 3 5 1 2 8

0 wax wax 94 1 1 6 1 4 0 1 4 4 1 4 3 -20 wax wax wax 1 2 3 1 3 8 1 4 9 1 4 7 -55 wax wax 1 0 4 1 1 9 1 3 9 1 5 4 1 5 2

--_ _ _ _

542 J. C. W. Chien. B. Rieger, R. Sugimoto, D. T. Mallin and M. D. Rausch

soluble fraction of the polymer obtained in a 2 O o C polymerization;

this fraction is insoluble in the next lower ranking solvent which is

acetone. The melting transitions of the polypropylene fractions had

been obtained. The D S C curves of the fractions from - 5 5 O C

polymerization are relatively symmetrical and sharp. In contrast,

those of the fractions from 7 O o C polymerization are broader and more

asymmetric. In fact the acetone and ether fractions have bimodal DSC

curves, respectively, and T, values as low as 54'C. Table 5 summarizes

the DSC results. The Tm for the C7i fractions, which is the refluxing

n-heptane insoluble polymer, are a few degrees higher than that for

the total polymer; the values for the other fractions decrease with

the decreasing rank of solvent.

The microstructures of the polymer fractions have been determined

by ' 3C-NMR and the steric sequence distributions are summarized in

Table 6, For the 7 O o C polymerization the fractions in the order of

increasing solvent ranking show regular increases in the mmmm and mmmr

pentads and regular decreases in the pentads having two or more r placements. The same holds true for all but the -55'CIE fraction. The

polymers obtained at O°C have occasional reversals in the progressions

of steric sequence distributions with respect to the solvent ranking.

Table 6 Steric sequence distributions of polymer fractions

TRl

OC

Pantad traction Triad traotion

Frsot ion Oiad nmn+ solublo i n *-a am It xr m8mu uu m u m u zajx larar KEU larrr MXII

70 A 7 3 . 5 0.62 0.12 0.15 0 . 3 4 0.16 0.13 0 .12 0.06 0.04 0.04 0 .05 0.06

70 6 80.0 0.72 0.17 0.11 0.52 0.11 0.053 0.013 0.053 o . 0 ~ 0 . 0 2 6 0.003 0 .053

86.2 0 . 7 9 0.lB 0.065 0.62 0.13 0.04 0 .092 0.046 0,007 0.009 0 .01 0.046

88.5 0.84 0.10 0.065 0.67 0 . 1 4 0.003 0 .066 0.027 0.005 0.004 0 .007 0.055

0 6 63 .0 0 .47 0 .33 0.20 0.26 0.16 0.05 0 .15 0.13 0 .052 0 .052 0.074 0.078

0 7 2 . 0 0.57 0.28 0.14 0.36 0.175 0.058 0.13 0.067 0.042 0.02s 0.067 0.059

0 83 .0 0 .73 0.20 0.074 0.11 0.17 0.052 0.13 0 .052 0.017 0.013 0.009 0.051

0 92.0 0.89 0.067 0.033 0.82 0.014 0.027 0.049 0.011 0.007 0.005 0.012 0.016

0 C7i 96 .0 0 .94 0.044 0.015 0.89 0.036 0.018 0.029 0.008 0.007 0 . 0 0 2 0 , 0 0 2 0.011

-55 I 66.0 0 .12 0.28 0.20 0.31 0.15 0.063 0.143 0.098 0.04 0 . 0 7 0.063 0.071

-55 c5 88.0 0.81 0.15 0 ,049 0.66 0.13 0.02 0.11 0.01 0.01 0 , 0 0 5 0.01 0 .029

-55 C6 91.0 0.86 0.10 0.044 0.77 0.064 0 .027 0.062 0 .032 0 , 0 0 3 0.007 0.003 0.034

-55 c7 94.0 0 . 9 0 0.069 0.027 0.79 0.094 0.016 0.041 0.024 0.004 0.001 0.006 0.02

C5 70

70 '6

'5

'6

c7

-55 c7i 96 .5 0 .91 0.028 0.01 0 . 9 2 0.013 0.008 0.023 0.004 0.001 0.007 0.001 0.012

38. Synthesis of Attisotactic and Ehtomeric Poljpmjylene 543

However, none of the fractions are "atactic" which should have [mml =

[rr] = 0.25 and [mr] = 0.5, etc. IR spectra had been recorded for all

the anisotactic PP fractions. The absorption bands at 841, 973, and

998 cm-' have ratios of A998/A973 and A841/Ag73 which bear linear

relationship to 13C-NMR determined [mmmm] with limits of unity for all

these quantities (Figs. 3 and 4).

0.3 04 0 5 06 0.7 0 8 0.9 1.0 [-I

Fig. 3 F i g . 4

Figure 3 13C-NMR: (0) t o t a l PP; (0) f rac t ion obtained by so lvent ex trac t ion .

Figure 4

13C-NMR: (0) total PP; (0) f rac t ion obtained by so lvent ex trac t ion .

Variation of the IR absorbance r a t i o , A99e/A973, versus [mmnunl by

Variation of the IR absorbance r a t i o , Ae4,/A973, versus [mmmm] by

The lower ranking fractions of PP obtained in 70°C polymerization

have T, and [ml diads which are very similar to the most stereoregular

PP obtained with the C P ~ T ~ ( P ~ ) ~ / M A O system.13) In the former, the A

and E fractions have T, ([ml) values of 54°C ([0.735]) and 86°C

([0.80]), respectively. The samples obtained with the latter system at

-3OOC and -60°C have T, ([ml) values of 55°C ([0.831) and 62OC

( [ 0.851 ) , respectively. Ewen' 3, also reported that the PP obtained

with rac-Et[IndH4I2TiCl2/MAO at 0°C has T, = 99°C and [mmmm] = 0.56.

This is very close to the total PP obtained with 1/MAO at 70°C which

has T, = 107OC (Table 5) and [ m m m m ] = 0.57 (Table 3).

It is reasonable to expect a correlation between T, and

isotacticity of PP. We found that they are related by an empirical

relationship based on Flory's theory of melting point suppression,

544 J. C. W. Chien, B. Rieger. R. Sugimoto, D. T. Mallin and M. D. Rausch

where Tmo is that for perfect-

ly regular polymer taken to be

184°C,22) and p is the prob-

ability for a given stereo-

unit. 0

- (l/Tmo) versus log [ m m m m l . Most of the data fit the given

7 Q? 0.8- 4

mo- - 0.6-

-

l-

Fig.5 is a plot of (l/Tm) -12 712 0.4- -

A

o.2kL- 0 9 8 7 6 loglmrnmrnl 5 4 3

line, however, the C5 and c6

fraction of Ooc polymerization do not. From the slope of the

plot, one can calculate A HU =

2.7 kcal- mol-l in agreement

with the literature values of

2.6 kcal mol- 137) and 2.3 kcal- Figure 5 Plot of (l/Trn) - (l/Trn') versus lOq[I"m] for fraCtiOnS Of misotact ic polypropylene: (0) T = 7 O O C ;

(0) Tp = -55°C; (A) T = O°C mol-l 23) P

P In the NMR spectra of the

O°C/E and 70°C/A fractions (Fig. 6), there were additional resonances.

The peaks numbered 4 to 7 can be identified with the carbon atoms in

the n-propyl and vinylidene chain end groups.

They are both produced by $-hydrogen chain transfer processes,

YH3 7*3 Zr-CH2-C-P 4 Zr-H + CH2=C-P

H

Where P is the polymer chain, to form the vinylidene end-group. This

is followed by propagation to produce the propyl end-group.

Zr-H + C3H6 d Zr-CH2-CH2-CH3 (3)

The remaining peaks 1 to 3 had been observed Soga

et a1.l') proposed a hydrogen transfer insertion in which the

propylene is incorporated in a direct "1 ,3-enchainmentI1. This process,

38. Synthesis of Anisotocfic and EhstomniC PolvproPlene 545

which requires a hydrogen atom

from the methyl group to be

transferred to the central

carbon atom of the propylene

unit, is difficult to envisual-

ize. Scheme 1 is proposed

instead. The normal 1,2-inser-

tion sequence (I) is inter-

rupted by a regio-chemical

error of 2,l -insertion. The

resulting species (11) has

significantly lower reactivity

toward monomer insertion, esti-

mated to be ca. 80-fold smaller

than for the normal propagating

chain (I),42) thus permitting

f3-hydride elimination to occur.

If the hydrogen comes from the

methyl group, a terminal olefin

is produced. It is depicted to

remain in the coordination

sphere of the metal (species

I11 in Scheme I). The 1,2-

insertion of this polymeric

olefin into the Zr hydride bond

should be a very facile pro-

cess. 13’) One more normal 1,2-

insertion of the monomer into

IV resulted in the observed

tetramethylene sequence (V).

The alternative elimination of

the hydrogen from the f3-methyl-

ene group of 11 produces an

internal olefin ( V I ) which is

not polymerized by ZN-catalyst.

‘I

sb

I__

P PM Fig. 6 ( a )

7 -

1 3 5 2 64

I i T i r I

7 a

i r

Fig. 6 ( b )

Figure 6 NMR spectra of (a)O°C-E and ( b ) 7 0 ° C fraction

Small amounts of ethylene impurity in the monomer had been

suggested to explain the presence of the tetramethylenes in PP.

However, the processes would have to involve a sequence of 1,2-propene

insertion, ethylene insertion and 2,l-propene insertion in order to


A t l ow A l / Z r r a t i o t h e r e a r e f o u n d t a i l t o t a i l u n i t s i n t h e PP c h a i n . P e a k s 7,8 i n F i g . 7 a r e e r y t h r o me thy l c a r b o n s and t h e a d j a c e n t peaks are d u e t o t h e t h r e o m e t h y l c a r b o n s . T h e r e f o r e , t h e i n s e r t i o n i s n o t h i g h l y r e g i o s p e c i f i c a t l o w A l / Z r r a t i o f o r t h e E t [ I n d I 2 Z r - C12 s y s t e m . A p p a r e n t l y , l a r g e a m o u n t s of M A 0 a r e r e q u i r e d f o r b o t h r e g i o - s p e c i f i c i t y a n d stereo-

form t h e sequence V. The p r e s e n c e of t e t r a r n e t h y l e n e s e q u e n c e i n d i c a t e s t h a t s e c o n d a r y

i n s e r t i o n o c c u r r e d t o a smal l e x t e n t u n d e r c e r t a i n c o n d i t i o n s . P r o - d u c t s c o n t a i n i n g t h i s r e g i o c h e r n i c a l error a re f o u n d m a i n l y i n t h e

e t h e r and a c e t o n e f r a c t i o n s . y, I

L A - CH, - C - P (1) H

2, l - insertion 1 (I I) L.Zr - C - CHICHI - P

H

melhylana H-transfer H-transfer

s e l e c t i v i t y .

L.Zr. H

+ 0 H monomer 1.2-Insertion 1 P - CH.CH=C

Scheme 1 Processes leading to "1,3-enchai~ment"

I ?

- 1 I ,

I , , , , , , , , , , ( , , , , , , , , , , I , , , , , , , , 45 40 35 30 25 20 15

PPM Figure 7 and Al/Zr = lo3.

NMR spectrum of the total polymers obtained at 30*C

38. Synthesis of AnisotncCfc and Elostomeric Polypmpylene 547

The three limiting stereochemical structures for polypropylenes

are atactic, isotactic and syndiotactic. Atactic polymer is amorphous

(0% crystallinity, m m = rr = 0.25 and mr = 0.5) such as the n-pentane

soluble fraction of the polymers obtained with 0-TiCl3/A1Et2C1 at

1 5°C,24) and with VC13/A1Et2C1 at 15'C. The isotactic polypropylene

should be insoluble in trichlorobenzene, has T, = 176OC and 75 to 85%

crystallinity. However, by common practice the polymer insoluble in n-

heptane (T, 1. 165'C, mm = 0.95 and Xc = 68%) is accepted as isotactic

polypropylene. To describe the polypropylenes obtained with the

metallocene/MAO catalysts as poorly isotactic or low in isotacticity

is insufficiently informative. Prof. T. Atkins and Ms. J. Atkins of

the Bristol University deemed the Greek prefix "an" to be the most

appropriate one to describe structures which deviate away from the

limiting structures. This has the advantage of being applicable to

both anisotactic (Tm > 165'C, [mnl > [rnl) and ansyndiotactic (Tm >

184OC, [rnl> [mnl). We are aware that this prefix has been used

previously by Natta and Corradini26) to mean polymers having an equal

number of randomly distributed substituents on both sides of the

chain, but this usage has not taken hold because of rare occurrence.

The PP having low T,, homosteric sequence, but appreciable Xc (vide

infra) is referred to as anisotactic PP (ani-PP).27t28)

THERMALLY STABLE Y -MODIFICATION

Highly isotactic PP crystallizes in the a-modifi~ation;~~) less

stereoregular polypropylenes can also crystallize in the 0 -30,31 and

Y - 29-31 )modifications. Powder x-ray diffraction patterns have been

obtained for several anisotactic PP fractions. The materials

precipitated from solution gave poor x-ray patterns and similarly for

samples quenched from melt. We found it necessary to heat the

specimens to above T, and cooled slowly over 2 4 hrs to room

temperature in order to obtain sharp diffraction patterns, though it

is not necessary to do the same in DSC measurements (vide infra).

There are no6 -phase reflections in any of the PP fraction; all the

patterns are combinations of reflections from thea - and y- modifications. The two most characteristic reflections have 2 8=18.3'

and 20' for the 0: - and y-phase, respectively, which are marked

accordingly in Fig. 8. The percent crystallinity was calculated by the

usual method. The percent of y-modification (5) was estimated from an empirical relations ,291

I (el

I, J! Figure 8 Powder x-ray diffraction patterns for samples (a)

? total polymer produced

m

P

with heterogeneous ZN catalyst, T = 163'C; (b) -55°C-C7i fraction; Tm=154'C;

(c) O°C-C7i fraction; T =144'C;

fraction; Tm=1300C; (f) 7OoC-C6 fraction; T = 113'C;

- m (d) -55'C-C7 fraction; Tm=132'C; (el O°C-C7 m -

(9) 70°C-C5fraction; T m = 105OC m

h - - x 100 cy- ha+ $

where h, and hy are the height

of the two peaks located at20

= 18.3" and 20°, respectively.

The results are summarized in

Table 7.

All the PP fractions

examined have Xc lying between

54% and 68%, which increases

with the order of solvent

ranking and decreasing Tp. The

-55"/C7,i fraction has higher

Xc and stereoregularity than

the other samples. Except for

the C7,i fractions, all the

other fractions crystallize

either largely or predominantly

in they -modification.

38. Sjmthesis of Auisotacfic and Elastomeric Pol'lene 549

(4)

Table 7 X-Ray diffraction results

on anisotactic polypropylene fraction

Sample xc, % c I % -

Heterogeneous 68.2 8

catalyst

-55"CIC, i 68.3 42

0"C/C7 1 67.9 70

-55" c/;; 65.2 87

0" CIC, 8.1 89

1-

70' c/c6 9.2 93

7OoC/C,j 54.4 100

The Y-modification of PP had been previously observed for low MW

materials obtained by thermal degradati~n,~'~) Y -irradiationt31f

special synthesis 31e) or extraction from commercial materials'la,').

The polymers were usually crystallized under p r e s ~ u r e . ~ ~ ~ , ~ ) However,

they -phases thus obtained in these materials are unstable and readily

undergo crystal-crystal transition to the a-phase upon heating. The

rate of this transformation had been found to depend on both the tem-

perature and the heating rate.39c) For instance, the DSC thermograms

of low MW PP obtained at slow heating rates 5 5"/min have only a single high T, for the melting of the a-phase, which indicates that

the rate of y to a transformation is faster than the heating rate.

Melting endotherms for both y- and a-phases were observed at 10°/min,

whereas a single endotherm at intermediate temperature was seen at

higher heating rates. Once the polymer sample is heated above 160°C

and cooled, noy-phase remained. Subsequent DSC scan exhibits only the

a -phase melting.

The thermostability of the y -modification of the present ani-PP

is in sharp contrast with the thermal instability of the previously

reported Y-form. The effect of heating rate on the melting endotherm

and the effect of cooling rate on the crystallization exotherm were


investigated for the 7oo/c6

fraction. In the former mea-

surement, the polymer sample

was first heated to 1 50'C and

cooled at 10'/min to room

temperature, then a second DSC

curve was recorded at heating

rates of 2.5, 5, 10, 20 and

4O0/min. The same T, of 118.5'

- + 0.5'C was obtained as shown

in Fig. 9, and the enthalpy of

melting was constant within

- +0.5 cal/g. For the second

measurements, samples heated

twice to 105OC were cooled at

different rates to observe the

exotherm. The crystallization

temperature was found to be

reproducible at 101.3, 98.1 , 95.4, 90.6 and 84.0'C for

cooling rates of -2.5, -5.0,

-10, -20 and -4O'/min, respec-

tively, indicating the polymer

crystallizes very slowly.

There is no a-phase endo-

therm at ca. 165'C using any

heating rate in DSC measure-

ment. This indicates the ab-

sence of y + a crystal-crystal

transitions and of appreciable

100 3 101.3

Figure 9

melting endtherm: (a) 2.5OC/min;

(c) 1OnC/m1n; (d) 20eC/mln; (e) 40°C/min and

the effect ofcooling rate on the crystalliza-

tion exotherm: (a') -2.5'C/min; (b') -5'C/min;

(c') -1O0C/m1n; ( d ' ) -20°C/min; (e l ) -4O"C/mIn.

The effect of heating rate on the

(b) S0C/min;

amounts of aphase. Secondly, the y-modification of the present aniso-

tactic PP reformed from the melt simply by cooling at any rate without

the aid of pressure. Finally, the crystallinity of the anisotactic PP

fractions are more than 54% even for the low T, samples. In contrast,

the low melting fractions of PP obtained with the classical ZN cata-

lysts have lower degree of crystallinity by comparison as shown in

Table 8. Finally, the PP previously reported to crystallize in the Y -

modification without applied pressure are very low in MW; the wn values are 2600 for thermally degraded PP31d) and 740 to 3900 by

38. SmthesiS of Anisotactic and ElastomeriC Polypmpylene 551

may not be attributed to low MW.

10:

CATALYTIC ACTIVITY

Most Ziegler -Natta catalysts have E f

maximum activity at some optimal Tp; 3103

the activity decreases at both lower . and higher temperature due to catalyst a activation and deactivation, respec- 2 lo! tively. The catalytic activities for +; . 1/MAO and 2/MAO increase monotonically 2 with Tp over an unprecedented broad $10-

range of T The data for 1/MAO were

already given in Table 1. The data for

both 1/MAO and 2/MAO are summarized in 1

Y

- P’

Table 8 Comparison of properties of the anisotactic polypropylenes

obtained with the 6-TiC13/A1Et2C1 and rac-Et[IndI2ZrCl2/MAO

,

c7 ,i 168 67-68 0.95

T = -55OC 154 68 0.92

TE = O°C 144 68 0.89

TE = -55OC 139 65 0.79

TE = O°C 140 48 0.82

c7 143 47 0.76

C6, Te = 70°C 113 134.5 59 39 0.67 0.64

Cg, TE = 7OoC 105 115 54 28 0.62 0.44

552 J. C. W. Chien, B. Rieger. R. Sugimoto, D. T. Mallin and M . D. Rausch

PP (mol-Ti.[M].h)-’ which is about one-fifth of the activity of I/MAO.

Radiolabeling determination found that about one -fourth of the Ti in the supported catalyst is active. Therefore, the difference in the

activities of the heterogeneous and homogeneous catalysts may be

attributed to lower utilization of Ti in the former, and that the two

catalysts have comparable intrinsic propylene polymerization rates for

their active species.

Tritium radiolabeling was used to determine the concentration of

active species, [C*], in 2/MAO by the reaction of the polymerization

mixture with CH303H.33) Since tritiated methanol reacts slower than

normal methanol with Zr-P and A1-P bonds, the specific radioactivity

o 0.1 0.2 a3

VIdd. n

Fig. 1 1

;/....,/ t

0 M 0.8 1:2

Fig. 12(a) W d d , 9

0 i i i i Wdd a @ , g

Fig. 12(b)

0 0s 10 16

lk ld 110: 8

Fig. 12(d)

oL as 10 ls

Wdd. n

Fig. 12(e)

Figure 1 1 Variation of metal-polymer-bond concentration with yield of total

polymer obtained at [ l ] - l o r n , T - 30.C and [Al]/[Zr] - 75,000 Figure12 Variation of metal-polymer-bond concentration with yields obtained

at (1 1 - 10pH. T - 30°C, and [Al]/[Zd - 3,500 for: (a) total, (b) E,

(c) C5, (d) C6, (e) C7 fractions.

P

P

38. Synthesis of Anisoiktic and Ehst& Polypropylene 553

4-

3-

I

in the labeled PP has to be corrected for this kinetic isotopic effect

(K.I.E.). The latter was measured by reacting polymerization mixture

with various amounts of CH303H from smaller than stoichiometric

equivalent to a large excess to obtain the maximum and minimum

specific activities, respectively. K.I.E. is the ratio of these

activities. The value determined from radioassay of the total polymer

produced with the 2/MAO catalyst is 1 .73 . This radiolabeled PP was

separated into four fractions soluble in E (diethyl ether), C6 and

C,; radioassay of the fractionated polymers yielded K.I.E. value of

1 . 7 7 , 1 .79 , 1 .72 and 1 .69 , respectively. The avera,ge value is 1 .74 in

good agreement with the K.I.E. for the total polymers. Also obtained

in this word is the K.I.E. of reactions with the 1/MAO system, which

C5,

v1.14, 0

F i g . 13(al Vl.ld. 0

F i g . 13(b) Yield a m ! 0

F i g . 13(c)

I 0 1 2 1 4

Vldd, 0 VI.ld. 0

F i g . 13(d) F i g . 13(e)

F i g u r e 13 V a r i a t i o n of metal-polymer-bond c o n c e n t r a t i o n w i t h y i e l d s o b t a i n e d

a t [ l ] = 1Opt-l. T = 3OoC and [ A l ] / [ Z r ] = 350 for: (a ) t o t a l , ( b l E , (c l C5,

( d ) C6, (el C, f r a c t i o n s . P

554 J. C. W. Chien. B. Rieger. R. Sugimoto, D. T. Mallin and M. D. Rausch

has a value of 1.50.

The metal-polymer-bond conc. [ MPB] varies with polymerization yield (Y), according to, 33)

* A plot of [MPBJt versus Yt extrapolated to Yo = 0 gives [MPB]o= [C lo. The results for polymerizations at 30°C and [All/[Zr1~3,500 (Figs. 1 1

and 12a) showed about two-thirds of the ansa-zirconocene complexes are

catalytically active. At the low [Al]/[Zr] ratio of 350 (Fig.l3a),

[C*] amounted to only 13 % of [ l ] .

The percentage of C responsible for the production of the n-th

anisotactic fraction by the 2/MAO catalyst has been determined. The

data of Figs. 12b to e and Figs. 13b to e, summarized to Table 9

showed that about half of the active Zr are responsible for forming

the c6 and C7 soluble polymers having higher Tm, whereas the remaining

half produces the C5 and E soluble polymers.

*

Table 9 Fraction of active Zr in Et[IndH412/MAOa

[c* I,/ [ zr I ,mol/mol [A1 1

[Zrl T E c5 '6 -

75,000 0.65

3,500 0.66 0.1 5 0.16 0.07 0.28

350 0.13 0.07 0.017 0.01 0.053

One attraction of the homogeneous ZN-catalyst is that it may

contain a single well-defined transition metal complex as the

catalytic species. This was the motivation of our earlier

investigation of the Cp2TiC12/A1R2C1 cataly~t.~ -7) However, the

heterogeneity in the microstructures of ani-PP and the radiolabeling

determination of C*distribution showed that there are two or more

catalytic species in the ansa-metallocene/MAO systems.

KINETICS

The total polymerization activity is measured by Rp,m,t, the

38. Synthesis of Anisotoctic and EIastomeric Polypropylene 555

amount of active species, [C"],, and the rate constant of propagation,

where the subscript t, denotes the total polymer and m for maximum

rate. In the case that polymers having different structures and M W can

be separated by solvent extraction into n fractions, then

* where wn and xn are the weight and mole fractions, respectively. [ C In can be calculated from the metal-polymer-bond concentrations in each

fraction (Figs. 12 and 13). In addition, from the slope of the plots

in these figures, the chain transfer rate constants, ktr,nA can be

obtained33) with eq. 5. The results summarized in Table 10 showed that

the rate constants for the active species which produced the various

fractions differ significantly. They can be grouped into two sets. The

k values are large for the C7 and C6 fractions; they are much smaller

for the C5 and E fractions. To the first order approximation, we

consider the presence of twoactive species Aand B, which produce the

more stereoregular and non-stereoregular PP, respectively.

Table 1 0 Rate constants for 1 /MA0 in propylene polymerizationa

[A1 1 kp,,,, (Msec) -1 k t P , n , sec-l - [zrl fraction

75,000 T 400 0.085

3,500 T 970 0.015

C7 1,840 0.015

c6 1,370 0.026

c5 80 0.003

E 130 0.0078

T 1,480 0.047

c7 2,550 0.027

c6 2,590 0.041

c5 97 0.0045

E 275 0.0027

350

Based on the radioassay we find comparable amounts of non-

specific and stereospecific species; [Bl = 0.31x[21 and [A] = 0.35x[2]. The small amounts of C5 and E soluble ani-PP's were produced

because of the small kp values for B.

The same conclusions can be made for polymerizations using

[A1]/[Zr] = 350. There are about equal amounts of A and B active

species present for a total corresponding to 13 % of 2. A species is

ten to twenty times more active than B and has five to fifteen fold

greater ktrA values. It is an interesting coincidence that in the case

of MgC12 supported TiC13 catalysts,33134) the isospecif ic sites also

have ten to sixteen times great k than the non-specific sites. P

EFFECT OF MA0 ON CATALYTIC ACTIVITY

The catalytic activity (A) of metallocene compound is strongly

dependent on the amount of MA0 used for activation. The results are

summarized in Table 11. In the case of the catalyst 2/MAO, the plot of

A versus log ([AlI/[Zrl) has a bell-shape. In contrast, 1/MAO exhibits

no catalytic activity at ratios of [AlI/[Zrl = 350 or less but the activity increases more strongly with the increase of [MAO], and did

not reach a maximum activity even at a ratio of [All/[ Zr] = 1 05.

Table 1 1 Effect of MA0 on polymerization activitya

- [All

[Zrl [ 21 [ l l 2/MAO 1 /MA0

[zrl,~M Activity x 1 0-61 gPP ( [ zrl [MI. hr1-l

100,000

75,000

35,000

6 , 500 5,000

4,000

3 , 500 700

350

145

80

4.2

10.8

10.8 12

10.8

12

12

10.8

10.8 12

10.8 12

50

50

14.2

1.12

1.71 13.9

4.39

9.2

8.3

5.80

4.49 1.2

2.28 0.003

1.36

1 .o

[C3H6] = 0.47 M I Tp = 30°C. a

38. Synthesis of Anisotactic and EIastomeric Polyprogykne 557

Polymerization by 2/MAO at a low [AlI/[Zrl ratio of 145 has a

short induction period, followed by two-stage increase of Re first to

8 x M-sec-’ in 30 min, then to Masec-’ after 3 h (Fig. 14a).

Increasing the [AlI/[Zrl ratio to 350 eliminates the induction period

but the two-stage increment of Re with time remained (Fig. 14b). For

polymerizations employing more MAO, there is only a simple rapid rise

followed by a moderate decay to a stationary rate of to a Rp,m polymerization. This simple kinetic behavior is like those

Time, h

Fig. 14(a)

4-

I 20 40 60

Time, min

Fig. 14(c)

A 5 6 Time, h

Fig. 14(b)

0 20 40 60 Time, min

Fig. 14(d)

Figure14 Variation of R with time f o r Et[IndH4]2ZrC12/MA0 catalyzed propylene polymerization at 3OoC and 1.68 torr monomer pressure: (a)[Zr] = 0.12,,M,[Al]/[Zr] = 145; (b)[Zr] = 26~M,[All/[Zr] = 350;

(c ) [Zr] = l.lpM;[Al]/[Zr] = 3,500; (d)[Zr] = l.ll~M,[Al]/[Zr] = 75,000

P


Et[IndI2ZrCl2 complex. In the

that the total amount of Al,

first approach the [MAO] is de-

creased and replaced with TMA so

[ A ~ I T = [ A ~ I T M A + [ A l l ~ ~ o l was q - 2 s kept constant. The resulting

effect on the catalytic activity, 2

Figure15 Variation of R

polymerization at 5OoC and 1.68 torr monomer pressure: (a)[Zr] = 10uM, [Al]/[Zr] = 4,000; ( c ) [Zr] = 11uM,[Al]/[Zr] = 10,000; (c)[Zr] = 20uM.

[Al]/[Zr] = 28,500.

with time for Et[Indl2ZrCl2/MAO catalyzed propylene P

3::

summarized in Table 12, showed

almost direct proportionality of

A with [MAOI. The polymerization

curves are given in Fig. 16. The

decrease of [MAO] by factors of

0.5 and 0.09 lowers the catalytic

activity of 1/MAO by 0.39 and

0.063 fold. The effect of TMA was

'1 1 4 I

0' i 2 3 5 6 Time, h

Figure16 Rp versu8 time curves for propylene poly-

merization at 30-C by 121 1'15.7uM and [Alj/[Zr] = 104i top to bottom MA0 only, [A1ITMA/[A1lMAO - 1

and [AIITMA/tAl]MAO 10.

38. Synthesis of Anisotocfic and Ehstorneric Polvpmpvlene 559

Table 12 Effect of substitution of TMA for MA0 on the

catalytic activity of 1 /MAOa

1 1 116 0 0 7.6 13.8

1 1 57.8 57.8 1 3.0 5.4

1 1 10.5 105 10 0.55 0.87

9.6 0.98 49 50 0

9.6 0.5 50 100 0 ~~ ~~

aTp = 3OoC, 50 ml of toluene.

also studied by the addi-

tion of TMA to a particu-

lar catalyst of [ l ] = 161.r

M and [MAO] = 0.14 M for

[A1IMAO/[Zr] = 8750. The

results in Table 13 showed

that the activity is

lowered with the addition

of TMA.

Though MA0 undoubted-

ly acts to methylate 1 or

2, this is however not its

most important role. Other

simple alkyl aluminum

Table 13 Effect of adding TMA on the

catalytic activity of l/MAOa

0 0 10.4 13.3

0.072 0.5 8.6 1 1 .o 0.14 1 4.7 6.0

1.4 10 2.2 2.8

a[ll = 16 p M l (MA01 = 0.14 MI Tp = 3OoC,

time = 1 hr, 50 ml toluene

compounds can also alkylate 1 or 2 but they do not give catalyst

active for propylene polymerizations. We showed above that the

replacement of MA0 with TMA proportionately reduces the catalytic

activity even though TMA is a powerful methylating reagent. It is

reasonable to assume that MA0 is needed to form the catalytic species. The results of spectroscopic studies prompted Long and Breslow 6)

to propose that Cp2TiC12 and RA1C12 react to form a cationic species

active for ethylene polymerization,


This mechanism was also favored by other investigator^^^-^^) and substantiated by the synthesis of catalytically active metallocene

cations for ethylene p~lymerization.~'-~~)

There are different reasons for simple alkyl aluminum compounds

to be poor activators for the metallocene compounds. Aluminum

trialkyls, such a s TMA, are probably insufficiently Lewis acidic to

produce the metallocene cation. In the case of alkyl aluminum

chlorides, they probably can produce the cation but the resulting

anion is unstable. The reverse reaction of eq. 8 occurs resulting in

termination and deactivation. The analogous processes are mainly

responsible for chain termination in common cationic polymerizations.

The corresponding fluorine containing anion would be much more stable

in this regard, which was used to advantage by Zambelli et to

obtain an MA0 free catalyst. They reacted group IV metallocene

dichlorides (L2MtC12) with a mixture of TMA and (CH3)2A1F to form an

homogenous catalyst which polymerizes propylene with stereoselectivity

comparable to the catalyst made with MAO. The authors proposed the

following equilibria,

L2MtCJ.2 + Al(CH3)3 + Al(CH3)zF LzMt(CH3)F + 2Al(CH3)2Cl (9) L2Mt(CH3)F + 2Al(CH3)3 F= [LzMtCH3]+"A12(CH3)sF] - ( 1 0 )

The formation of the metallocene cation is attributed to the high

ionicity of the Mt-F bond, and the catalytic activity is due to the

stability of the Al2(CH3I6F anion.

According to the above discussion, it is reasonable to

postulate44) the reaction between L2MtX2 and MA0 to produce the ion-

couple ,

The halogenated MA0 anion is stabilized by electron deficient bond

depicted as A. The reverse process of eq. 1 1 can be thus prevented.

coactivator as MAOga) and aluminoxane of high aluminum , , 0 - Al, alkyls to be even more inferior. Two factors can con-

tribute toward the differences: lower Lewis acidity i.e.

/cH3 Ethyl aluminoxane was found to be not as good a

0o Cl--Al

0 , smaller equilibrium constant for eq. 1 1 and weaker Al- CH3 0-

A L

Cl--Al bonds.

38. Synthesis of Ankiofoctic and Elastometic Polypropylene 561

The observed behavior of replacement of MA0 by TMA can be

understood because of the equilibrium competes against eq. 11.

It is well recognized that the metallocene catalyst requires very

large quantity of MA0 as activator in order to reach the high

potential catalytic activity. In this study only 13 % of 2 became

catalytically active at the low [Al]/[Zr] ratio of 350. The induction

period and two-stage rate acceleration at low to moderate [Al]/[Zr]

ratios indicate slow rate of activation. Therefore, the value of the

equilibrium constant for eq. 1 1 must be quite small and large amounts

of MA0 are needed to shift the equilibrium to the right. The

equilibrium is also not reached quickly.

The different dependences of catalytic activities of 1 and 2 upon

[MAO] are interesting. The bell-shaped curve f o r 2/MAO may be

explained by the following. At low [All/[Zr] ratio, the increase of

activity with [MAO] reflects the formation of C*,

where K is the equilibrium constant for eq. 11. The decrease of

activity with very large amounts of MA0 may be attributed to excessive

complexation of MAO,

C* + mMAO K' C* * (MAO),

where m is a small integer of 1 or maybe 2. The vacant coordination

position in C .(MAO), for the complexation of propylene became

unavailable.

In the case of 1/MAO, it requires larger [Al]/[Zr] ratio to

become active than for 2/MAO. Furthermore, maximum activity was not

reached even at a ratio of 10'. This indicates that both K and K'

values are smaller for the catalyst 1/MAO.

*

The polymers obtained using the 1/MAO catalyst at T = 5 0 ° C

produced 17 wt % of C7 insoluble PP. This fraction increased to 75% at

Tp = 2OoC. No C7 insoluble PP was produced at Tp 2 7OOC. This suggests that more of the stereospecific species of the A kind are formed in

this catalyst than in 2/MAO or that the catalytic species in the

P

562 J. C. W. Chien. B. Rieger. R. Sugimoto, D. T. M a h and M. D. Rausch

former has higher propagation rate than the ones in the latter system.

On the other hand, the polymers obtained with the latter catalyst

generally have more homosteric pentads.

[Al]/[Zr] ratios of 1.1 x l o 3 , 2.5 x l o 3 and 16.4 x l o 3 and [ l ] =

M at Tp = 3OoC, 2.1 and 1.5, respectively; there is also an effect on the Mn values which are 3.29 x l o 4 , 3.36 x l o 4 and 4 .8 x l o 4 , respectively.

MA0 also has significant effect on MW distribution. Using

the R,/R, of the total PP are 2.3,

EFFECT OF MA0 ON STEREOSELECTIVITY

There is a strong effect of MA0

on the distribution of soluble PP

fractions. The ani-PP obtained with

2/MAO catalyst contained 8.5% of C7 and 2.9% of C5 fractions at [All/[Zr]

= 7 5 , 0 0 0 . For very low [Al]/[Zr]

ratio of 1 4 5 , there is formed only

11.7% of C 7 but 30.6% of C5 fractions (Table 1 4 ) . Therefore, large amount of MA0 enhances the formation of more

ordered PP.

The stereochemical control of

2/MAO is also lowered by either the

substitution of M A 0 with TMA or the

addition of TMA (Table 15) . In the former experiments no. 1 -

Table 1 4 Fractionation of

anisotactic polypropylenea

[All Wt% of polymer soluble in

[Zrl c5 '6 c7

75,000 2.9 11.5 85.6 35,000 3.4 10.3 86 .3

3,500 4 .4 14.3 81.3 350 8.8 18.0 73.2 145 30.6 57.7 11.7

~~

aObtained from 30°C polymerizations catalyzed by 2/MAO there

was no C7 insoluble polymer in all the products.

3 the c 6 and C7 fractions decrease and the E fraction increases

steadily with the progressive substitution of TMA for MA0 while main-

Table 1 5 Effect of TMA on the stereoselectivity of 2/MAO

Run [I] [A~IMAo [A~ITMA [A~ITMA Wt% of polymer soluble in No. !JM mM mM [ A1 1 MAO E c 5 '6 c7

1 1 1 0 0 0 0.48 0.59 2.59 96.3 2 1 5 5 1 0.96 0.50 6.73 91.8 3 1 0.9 9.1 1 0 4.3 1.65 16.7 77.4 4 1 10 100 1 0 1.96 1.84 13.4 82.8

Table 16 Steric sequence distributions of anisotactic polypropylenesa

Catalyst [ A l l / [ z r l System ratio mrmm+

mm m r rr mmmm mmmr rmr mmrr r m r r m r m r rrrr m r r r m r r m

2/mo 2/MAO

2 /MA0

2 /MA0

1 /MA0

1 /MA0

1 /MA0

1 /MA0

75,000

35,000

3,500

350

2,500

16,400

16, 400b

1,100

0.949

0.937

0.932

0.935

0.872

0.885

0.883

0.680

0.039

0.038

0.049

0.047

0.079

0.074

0.074

0.202

0.012

0.017

0.018

0.018

0.049

0.041

0.043

0.118

0.921 0.027 0.001 0.025 0.013 0.001 0.000 0.002 0.010

0.902 0.034 0.001 0.034 0.010 0.003 0.000 0.003 0.014

0.899 0.032 0.001 0.032 0.016 0.001 0.000 0.003 0.015

0.898 0.036 0.001 0.029 0.017 0.001 0.000 0.003 0.015 Fo

0.818 0.045 0.009 0.049 0.021 0.009 0.014 0.014 0.021 Y" 0.835 0.037 0.013 0.046 0.017 0.011 0.011 0.012 0.018 B.

0.834 0.038 0.011 0.045 0.021 0.008 0.011 0.013 0.019

0.577 0.082 0.021 0,084 0.078 0.004 0.042 0..035 0.041

W

8

k F

1 aTotal polymer unless otherwise s tated, Tp = 3OOC; bn-heptane in so lub le f rac t ion .


taining [AllT constant. A similar effect was seen in run 4 where TMA

was added to the polymerization system.

Lowering of [MAO] resulted in ani-PP containing lowered

populations of homosteric sequences [ m m l and [ m m m m l as shown by the

data in Table 16.

ORIGIN OF STEREOSELECTIVITY

Using a Cp2Ti(C6H5)2/MA0 catalytic System, Ewen’ 3 , polymerized

propylene at -45OC to obtain ani-PP containing 85% of meso diads. It

was concluded that the last monomeric unit chains can select the

particular enantioface of propylene. At higher Tp this type of

stereoregularity is lost and a substantially atactic PP is formed.

Consequently, this nonchiral catalyst is incapable of selecting

enantioface in the synthesis of i-PP above Tp = O°C.

In the case of the chiral complex 1 or 2 , assuming its

crystalline structure’ ’ b, is maintained in the catalyst, there are four possible transition states for each (R) or (S) complex.44)

Fig.17 showed the states for the (R) antipod.

The bulky propa-

gating chain (P) and

the methyl group of

the monomer both occu-

py the positive quad-

rants ( + 1 and +2).

Based on consideration

of non-bonded inter-

actions the energies

of the transition

states decrease in the

order lb Re > lb Si - la Si > la Re, which

is the basis for the

stereoselection of the

particular enantioface

of the monomer for

1,2-addition. Pino et

al. 4 5 ) used (-)(R)-

Et[IndH412Zr(CH3)2/MA0

to Dolvmerize Droovl-

L- 1

l a Re-meso

I b Si-meso

-1

l a S i d racernic

I t

1

1 b Re-racemic

Figure 17 Possible transition states for the hydroolego-

merization with ( - 1 (R)-Et[IndH,],Zr(CH,),.

38. Synthesis of Ankotactic and EhstorneriC Polyproplene 565

ene at O°C in the presence of H2. The resulting oligomer (Rn up to

4000) has positive optical rotation; the hydrogenated trimer has the

(+)(S) configuration. This demonstrates that la Re is the prevailing

transition state under these conditions. The high stereoselectivity

([m] 9 8 % ) results from the cooperation of the active center

chirality and the conformation of the last monomeric units of the

propagating chain. The steric sequence distributions for the total

ani-PP samples given in Table 3 had been compared with the models of

stereochemical control by the enantiomorphic site (E) and by the

combined E and chain-end effects (E/C).25) The calculated distribu-

tions with the E/C model are in better agreement with the observed

distributions than the E stereochemical control model.

The electronic structures of bis(cyclopentadieny1) metal

complexes have been considered by Lauher and H~ffmann.~~) The bent 3d0

Cp2Zr fragment has three nonbonding molecular orbitals lal, b2, 2al in

order of increasing energy. The Cp2Zr+R complex has the highest

Table 17 Molecular orbitals for the 36" Metallooen. l i g m d complexes

X

Complexa Bonding o r b i t a l Non-bending o r b i t a l s

CpzZr l igand CpzZr l i g s n d C&r l igand

CP, +/01 Z r

c,' 'R

Zai(a1 ' ) a i (R) 2ai ( a i l ) a, (L) l a i (a1 ' ) a1 (L)

is t h e propagating chain, 01 is t h e o l e f i n , L is MAO, Zr-s is theCpZZr b i s e c t o r , a l l t h e l igands l i e i n t h e y s plane; bspecies i n parenthes is a r e f o r C s symmetry.

566 J. c. W. Chien. B. Rieger, R. Sugimoto, D. T. Mallin and M. D. Rausch

bonding molecular orbital derived from the 2al orbital of Cp2Zr and a,

orbital of the propagating chain R (Table 1 7 ) . But the 2al orbital is

the highest in energy of the three available valence orbitals, a

geometry in which the R- is of€ the Zr-z twofold axis but still in the

yz plane, have in addition good overlap with l a l and/or b2, is

energetically more favorable than R- along the Zr-z axis. The

complexation of olefin involves firstly the overlap of aln orbital

with 2al orbital. For the same reason as above, overlap of the olefin IT* with the lal of Cp2Zr would result in more stabilization than

olefin complexation in the symmetrical position for the ZR-olefin

bond. The Cp2Zr+R(olef in)Zr complex molecular orbitals are given in

Table 17 . Since there are three valence orbitals for the Cp2Zr

fragment, an additional ligand, i.e., MA0 or MAO-, can occupy the

vacant coordination position with the relevant orbitals found in Table

1 7 .

STRUCTURE OF ANISOTACTIC POLYPROPYLENES

Stereo-insertion errors lead to the formation of ani-PP. There

are two probable mechanisms.

( 1 ) Two-state mechanism with chain migration

(a) Single r insertion error

la-(m)h-P + C3H6 ----$ lb-r(m)h-P

Ib-r(m)h-P + ic3H~(si) 4 lb-(m)ir(m)h-P

(b) Double r insertion error

lb-r(lll)hdP + C3H6 4 la-rr(m)h-P

la-rr(mIh-P + iC3H6(Re) 4 la-(m)irr(m)h-~

(2) One-state mechanism without chain migration

(a) Single r insertion error

la-(mIh-P + C3H6(Si) la-r(m)h-P

la-r(mIh-P + iC3H6(Re) 4 la-(m)ir(m)h-P

(b) Double r insertion error la-(mIh-P + C3H6(Si) 4 la-rr(m)h-P

la-rr(mIh-P + iC3H6(Re) 4 la-(m)irr(m)h-~

( 1 9)

(20)

The two kinds of insertion errors, single r and double r , have important morphological consequences. In the former the two m sequences on each side of the r placement have opposite helical

38. Synthesis of Anko&ctic and EIastomeriC PolupropUlene 567

Table 1 8 Comparison of stereochemical sequence distributions

Samplea Sample desig. [mmmrl/ [mmrrl/ [mrrml desig. [mmmrl/ ~mmrrl/ [mrrml

80°/T

70°/T

70°/A

7 0 ° / E

70°/C5

7O0/c6

5Oo/T

Oo/T

O o / E 0°/c5

2.1 1.5 1

1.9 1.4 1

2.5 2.2 1

2.8 1?8 1

2 . 0 2 . 0 1

2 . 5 2.1 1

2.8 1.4 1

3.9 2.4 1

2.0 1.9 1

3.5 2.1 1

0°/C6

0°/c7, i

-55"/C5

-55O/C7

-55'/c7,1

0°/c7

-55'/E

-55'/c6

3O0/T-lb

30°/T-2b

3.2 2.5 1

2.8 3.0 1

3.3 2.6 1

2.1 2.0 1

4.4 3.1 1

1.9 0.9 1

4.7 2.1 1

1.9 1.9 1

5.7 2.6 1

5.7 2.4 1

~

aT denotes total polymer; b300/T-1 was obtained at Tp - 3OoC and Al/Zr = 1.64 x lo4; 30°/T-2 was obtained at Tp = 3OoC and Al/Zr = 1

x 103.

configurations whereas they are the same on each side of the rr

placement. The latter should dominate if the stereochemical control by

the enantiomorphic site prevails. In this instance,47) [mrl = 2 [rrl?

and [mmmr]:[mrnrr]:[mrrrn] = 2:2:1. The [mmmr] in the twenty samples are

mostly greater than [mmrrl and much larger that 2[mrrml (Table 1 8 ) .

This suggests that there are present much more single r insertion error than is expected for the enantiomorphic site control model. The

quantitative aspects of the relative sequence distributions are

rendered somewhat uncertain because the C9 and CIO resonances

associated with the n-propyl end group contribute toward the pentads

being compared.

Polypropylene with highly isotactic stereochemical order

crystallizes in the a -phase modification which usually does not

exhibit h = k = odd Therefore, the unit cell

accommodates randomly four chains o f left-handed cataclinic helix

(methyl group up, A chain), left-handed cataclinic helix (methyl group down? B chain) , and right-handed counterparts. Annealing can reduce this randomness as evidenced by the appearance of weak h + k = odd

reflections; the crystal structure was described as belonging to the

space grouy ~ 2 , fC.29blc)


The proposed triclinic cell geometry of the y-phase appears to be

closely related to the monoclinic a-phase cell. 3latb) One can

visualize that the former can be obtained from the latter by a simple

shear between the (040) plane along the a - a ~ i s . ~ ~ ~ ) The two cells have

nearly the same densities. There does not appear to be any

according to conformational analysisI3ld) why either

one should be more stable than the other. Natta and C~rradini~'~)

suggested that the y-form becomes the preferred form if there is

present \A and blocks along each chain, i.e., stereoblock copolymer.

Such materials can have alternate 4 and b sections of either a left- or a right-handed helical configuration with the Me-C bonds

alternately pointing ''up'' or "down". The methyl groups, which largely

determine the packing, will lie all ''up'' or "down" in one type of

helix. 'Therefore, there will be a discontinuity where the A configuration changes over to 2 . The crystallization behaviors are consistent with the y -form packing capable of withstanding the discontinuity in

the helix better than the a-form without partially disrupting the

crystallinity.

Previous polypropylenes found to favor the y-modification, which

are thermally unstable with respect to the a-modification, were very

low in MW; the FIn values were 2600 for thermally degraded polymers31d) and 7 4 0 to 3900 by special synthesis.31e) This is compared with Rn I s

of 9,000 to 90,000 for the present anisotactic polypropylenes.

Therefore, the ani-PP formed by the chiral metallocene catall ;t, which

crystallizes preferentially in the thermally stable y-form, probable

are comprised of chains containing frequent with discont nuity in

their helical configurations.

PROOF OF TWO-STATE PROPAGATION MECHANISM

The two-state propagation mechanism cannot be tested by physical

and spectroscopic properties of the ani-PP or kinetic results. We have

reasoned that if the metallocene complex have dissimilar o5 -systems, and that their stereochemical controls of the states associated with

them are different, then very different kind of PP may be produced. In

particular, if one state is isospecific and the other state is

nonspecific, and if a chain propagates alternately via these two

states, then the macromolecule would contain alternate crystallizable

and noncrystallizable segments. such material would be a thermoplastic

elastomer of homopolypropylene.

38. Synthesis of Anisotactic and EIastomeric Polypropylene 569

A new =-complex =-ethylidene( 1 -n5-indenyl)-

(1- n'-tetramethyl Cp) dichlorotitanium was synthe-

sized4'), which has the probable structure (31 , based

on steric considerations. The polymers obtained at Tp

= 50'C and 25'C are designated TPE-PP-50' and TPE-PP-

25', respectively. Aside from a very small amount of

acetone soluble material, the polymers are completely

soluble in refluxing ethyl ether indicating uniformi-

ty of structure. They are also characterized by

narrow molecular weight distributions. According to

GPC using columns calibrated with polypropylenes of known mw, TPE-PP- 50'C has Rn = 66,600, Rw = 127,000 and R,/R, = 1.9 and TPEiPP-25'C has

Rn = 98,400, A, = 164,000 and Mw/Rn = 1.7; the degree of crystallinity

was found by Roland analysis of x-ray powder patterns obtained on

samples annealed between 30'C and 45'C to be 28.6 5 0.5% and 26.5

0.4%, respectively. The polymers exhibit more than one melting endo-

therms; the transition temperature (Tm) and enthalpy AH^) obtained by DSC on samples annealed at 30'C for 12 h are given in Table 19.

Annealing at lower temperatures resulted i lower T, which indicates a

dependence of the size and order of crystalline domains on crystal-

1 i zat ion conditions.

The dynamic storage modulus (GI) measured at 1 rad s- ' as a

function of temperature showed three orders of magnitude decrease

between 60' and 80'C due to the melting transition. G' increases only

slightly with frequency at 50'C but increases strongly with frequency

(3)

Table 19

Mechanical and thermal properties of TPE polypropylene

Sample TPE-PP-50' TPE-PP-25'

Strength, MPa 3.97 12.1

Strain to break, % 525 1260

Recovery after break, % 86 94

1.47 0.56

51.2, 66.0 53.1, 63.8

3.26 2.93

aSamples annealed at 30'C for 12 h before DSC scan.

570

at

J. C . W. Chien. B. Rieger, R. Sugimoto, D. T. MaUi and M. D. Rausch

Table 20 Elastomeric properties of TPE polypropylenes

Sample TPE-PP-50' TPE-PP-25'

Strain, % 100 200 300 100 200 300

Stress, MPa 3.13 3.39 3.53 3.07 3.30 3.56

Recovery, % 93 91 83 97 96 92

100'C indicating an elastomeric state in the former but a single

phase melt state in the latter. Stress-strain curves obtained on

dogbone samples (molded at lOO'C, annealed at 60'C for 2 h) showed

very strong mechanical properties (Table 19). In particular, TPE -PP - 25' did not break until stretched beyond 1260%. The polymers exhibit

excellent elastic recoveries (Table 201, The strain recovery is better

than 90% for TPE-PP-25' after elongation of 100 to 300%. These

properties can be explained only by the presence of physical

crosslinks due to crystallization of stereo-regular segments of the

polypropylene chains. The molecular weight between crosslinks (M,) was

estimated from the equilibrium modulus (Ge ) which was measured at

5OoC, 0.5% strain, and stress relaxed for 10' sec. The estimates f o r Mc ( = density RT/Geq) are 2.0 x lo3 and 4.4 x lo3 for TPE-PP-50' and -25', respectively. Since the crystallizable segments in the polymer

chains must be quite short as indicated by the low Tm, there are many alternating crystallizable and noncrystallizable segments, of the

order of twenty.50) These polymers contain low homosteric pentad

populations.51)

The properties and structures of the TPE-PP's can only be

explained if the macromolecule grows alternately on two-states 3a and

3b as follows

where kp's are greater than kab, kba. The resulting polymer is

microphase separated into crystalline and amorphous domains, and the

former act as physical crosslinks. Above Tm, the polymers are linear

viscoelastic.

38. Svnthesis of Anisofattic and Ehstomeric Polupropuk 571

The bridging carbon

in 3 is chiral and can

have the polymer chain

either syn (3a) or anti

(3b) to the ansa-methyl

group during polymeriza-

tion. They are probably

the two states responsi-

ble for the synthesis

first time ever of homo-

geneous thermoplastic

elastomer comprised of a

single monomer. 52,53)

3a 3b

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J. C. Wi ttmann I J. Po lym. Sci. , Polym.Phy s. I 24,2 0 1 7 ( 1 986 ; (e )D.R.Morrow , B.Z.Newman, J.Appl.Phys., 39,4944( 1968); (f )V.P.Krestev, B.Dovreva,

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(b) J.C. W.Chien, A.Razan, ibid. , 26,2369 (1 988 1; (c J.C.W.Chien, B.P.Wang , ibid., ~,1539(1989);(d)D.T.Ma1linI M.D.Rauch, J.C.W.Chien, Polym.

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in press

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J.Am.Chem.Soc., 107,721 g(1965)

3 8. E.Gianne t i I N.Martino , R.M. Maz zocchi , J.Polym.Sci. ,Polym.Chem.Ed. I

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Appl.Sci.N.Y.p.3.

26,3089( 1988);

574 J. C. W. Chien. B. Rieger, R. Sugimoto, D. T. MaUin and M. D. Rausch

45. P.Pino, P.Cioni, J.Wei, J.Am.Chem.Soc. =,6189(1987)

46. J.W.Lauher, R.Hoffmann, ibid., 98,1329(1976)

47. Test for stereocontrol mechanism by the steric sequence

distribution has been discussed in numerous publications, two

monographs giving complete treatments are: (a) F.A.Bovey, "High

Resolution NMR of Macromolecules", Academic Press,, N.Y. , 1972; (b) Y.V.Kissin, "Isospecif ic Polymerization of Olef in", Springer-Verlag,

N.Y.,1985

48. The crystal structures of disordered and ordered aphase of

isotactic polypropylenes have been determined by: ( a ) G.Natta,

P.Corradini , M.Cesari , Atti Accad.Nazl.Lincei Rend.Classe Sci.Fis. , Mat.Na-t., 2l,365(1 956); (b) LMencik, J.Macromol.Sci.Phys.B, 5,101

(19721;(c) M.Hikosaka, T.Seto, Polym.J., 5,111 (1973) 49. D.T.Mallin, M.D.Raudch, Y.G.Lin, J.C.W.Chien, 2.Am.Chem.Soc. in

press

50. This crude estimate assumes the crystallizable segments are

comprised of about twenty monomer units. It is dependent upon the

crystallization conditions.

51. The average steric pentad distributions for 3 by the methyl I3C

NMR spectrum are: [mmmm1=0.40;[mmmr1=0.16;[rmmr]=0.043;[mmrr1=0.15;

[mrmm l+[rmrr ]=0.07; [rmrm]=0.034; [rrrr 1=0.02; [rrrm ] =0.043; [ m r r m ] =0.07

52. Polypropylenes exhibiting elastomeric properties have been

obtained by Tullock and coworkers'

Ti, Zr and Hf catalysts. Their materials contain chains soluble in

ethyl ether, hexane, heptane, octane, as well as octain-insoluble

ones. Hysteresis curves showed 110% permanent set after 300%

elongation.

53. (a)C.W.Tullock, F.N.Tebbe, R.Mulhaupt, D.W.Overal1,

R.A.Selterquist, S.D.Itte1, J.Po1ym.Sci.Part A, 27,3063(1989);

(b)J.C.Collette, C.W.Tullock, R.N.MacDonald, W.H.Buck, A.C.L.Su,

J.R.Harrel1 I R.Mulhaupt , B.C.Anderson, Macromolecules, 22,2851 (1 989)

using alumina-supported bis(arene)

Studies in Surface Science and Catalysis Advisory Editors : 6. Delmon, Universite Catholique de Louvain, Louvain -la - Neuve, Belgium

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Structure and Reactivity of Surfaces. Proceedings of a European Conference, Trieste, Italy, September 13- 16, 1 988 edited by C. Morterra, A. Zecchina and G. Costa

Zeolites : Facts, Figures, Future. Proceedings of the 8th International Zeolite Con- ference, Amsterdam, The Netherlands, July 10- 14, 1989 edited by P. A. Jacobs and R. A. van Santen

Hydrotreatlng Catalysts. Preparation, Characterization and Performance. Pro- ceedings of the Annual International AlChE Meeting, Washington, DC, November 27 -December 2, 1988 edited by M. L. Occelll and R. G. Anthony

New Solid Acids and Bases -their catalytic properties by K. Tanabe, M. Mlsono, Y. Ono and H. Hattori

Recent Advances In Zeolite Science. Proceedings of the 1989 Meeting of the British Zeolite Association, Cambridge, 17- 19 April, 1989 edited by J. Kllnowski and P. J. Barrle

Catalysts In Petroleum Reflnfng 1989. Proceedings of the Conference on Catalysis in Petroleum Refining, Kuwalt, March 5-8, 1989 edited by D. L. Trlmm, S. Akashah, M. Absi-Halabi and A. Bishara

Future Opportunlties In Catalytic and Separation Technology edited by M. Misono, Y. Moro-oka and S. Klmura

New Developments In Selective Oxidation. Proceedings of an International Sym- posium, Rimini, Italy, September 18-22, 1989 edited by 0. Cent1 and F. Triflro

Catalytic Olefln Polymerization. Proceedings of the international Symposium on Re- cent Developments in Olefin Polymerization Catalysts, Tokyo, October 23- 25, 1989 edited by T. Kell and K. Soga

Documents

Catalytic Olefin Polymerization: Proceedings of the International Symposium on Recent Developments in Olefin Polymerization Catalysts, Tokyo, Octobe