Influence of Internal Donors on the Performance and Structure of MgCl2 Supported Titanium Catalysts for Propylene Polymerization

Full Paper

Influence of Internal Donors on thePerformance and Structure of MgCl2 SupportedTitanium Catalysts for PropylenePolymerization

Gurmeet Singh, Sukhdeep Kaur, Umesh Makwana, Rajendra B. Patankar,Virendra K. Gupta*

An insight on the influence of ethyl benzoate (EB) and diisobutyl phthalate (DIBP) as internaldonors, differing in coordination nature on the structural aspects of MgCl2 matrix in high-performance MgCl2-supported titanium catalysts was developed using FTIR spectroscopy andWAXD studies. The analysis of the >C––O stretching IR band of internal donors showed theircoordination to (104) and (110) lateral cuts of MgCl2 matrix. Transformation of magnesiumethoxide {Mg(OEt)2} to MgCl2 during catalyst preparation resulted in different MgCl2 phases,namely the a-form, b-form, and the disordered d-form, which were analyzed byWAXD studies.The results fromWAXD showed the relative preference of a-form over b-form in case of DIBP-based catalysts, which might be due to inter-layer bridging between adjacent layers due tothe bidendate nature of DIBP. This can be one ofthe reasons for the high productivity of dialkyl-phthalate-based catalysts in comparison toethyl-benzoate-based catalyst systems.

Introduction

Modern heterogeneous Ziegler-Natta catalysts for the

industrial production of polypropylene are MgCl2-sup-

ported titanium catalysts,[1-4] providing high productivity

and microstructure control of polypropylene.[5–9] The main

focus in the production of polypropylene is the continual

development and improvement of existing catalysts, to

achieve higher productivity with stereospecific control for

the desired physico-chemical properties of the product. The

wider applications of polypropylene in vast end uses is due

G. Singh, S. Kaur, U. Makwana, R. B. Patankar, V. K. GuptaCatalyst & Material Research Technology CenterReliance Industries Ltd., Hazira Complex, Surat, Gujarat – 394 510,IndiaFax: þ912616635879; E-mail: [email protected]

Macromol. Chem. Phys. 2009, 210, 69–76

� 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

to good mechanical properties, chemical resistance, and

excellent insulation characteristics.[10–12]

Over time, the Ziegler-Natta catalysts have evolved from

simple TiCl3 crystals to TiCl4 supported on morphological

MgCl2 crystallites. MgCl2 is the support of choice because

of its similar crystal structure to that of TiCl3, the active

catalyst species. MgCl2-supported catalysts have the

advantages of higher catalyst productivity, controlled

morphology, and higher stereospecificity. Understanding

of MgCl2-supported titanium catalysts at the atomic level

still remains a scientific challenge. MgCl2/TiCl4/dialkyl

phthalate and MgCl2/TiCl4/ethyl benzoate systems repre-

sent successive generations of high-productivity MgCl2-

supported catalyst systems. Dialkyl phthalate systems

have substantially high productivity in comparison to

ethyl benzoate systems: the reasons for this high

productivity are still not clear. Spitz et al. recently reported

DOI: 10.1002/macp.200800486 69

G. Singh, S. Kaur, U. Makwana, R. B. Patankar, V. K. Gupta

70

that internal donors might not have any direct role in the

active site formation.[13] Thus, the role of internal donors

for stabilizing MgCl2 crystallites and blocking nonster-

eospecific/low-productivity sites became very critical.

Particles of activated MgCl2, the support structure, are

composed of irregularly stacked Cl–Mg–Cl sandwiches

(layered structure). Formation of the active catalyst

requires distortion of the MgCl2 crystal structure, which

is supported by theoretical[14–16] and experimental stu-

dies.[17–20] Activated MgCl2 supports are characterized by

small crystallites with stacking faults of triple layers, and

structurally disordered d-MgCl2 phases, producing high

surface areas.[21–23] Andoni et al.,[24–27] using atomic force

microscopy (AFM) and scanning electron microscopy

(SEM), and Mori et al.,[28] using high-resolution transmis-

sion electron microscopy (HRTEM), have observed and

confirmed the presence of well-defined MgCl2 crystallites

with preference for the formation of less Lewis acidic (100)

or (104) and more Lewis acidic (110) lateral cuts. Based on

the electroneutrality reason[16] and on the analysis by

Giannini,[29] the (100) and (110) lateral cuts have

magnesium atoms coordinated by five and four chlorine

atoms, respectively. Busico et al. recently reported, based

on periodic discrete Fourier transform (DFT) and high-

resolution magic-angle spinning (HR-MAS) studies, that

the less Lewis acidic plane should be designated as (104)

for a-MgCl2 phase[30] and the same has been extended by

Andoni et al.[27]. The (104) and (110) lateral cuts (Figure 1)

are the surfaces where internal donors, titanium chloride

species, and external donors bind to coordinatively

unsaturated Mg2þ ions. Recent publications suggest that

TiCl4 may not form complexes with MgCl2 on (104) lateral

cuts, owing to weak Lewis-basic sites, while forms stable

complexes with Mg2þ ions at (110) lateral cuts.[31–33] Thus,

(110) lateral cuts become critical for active-site formation,

and the core for stereospecific polymerization of poly-

propylene.

Figure 1. MgCl2 matrix depicting (104) and (110) lateral cuts withfive and four coordinated magnesium ions, respectively, andthree coordinated magnesium ions at edges. Dark gray spherescorrespond to the chlorine and light gray spheres to the mag-nesium ions.



Structural understanding of high-performance MgCl2-

supported titanium catalysts becomes essential for

improvement in the polymerization performance. The

effect of catalyst type on the productivity, properties, and

performance of polymer requires detailed insight into the

nature of the MgCl2 support. The aim of the present study

is to understand the structural characteristics of the MgCl2

matrix through component analysis from wide-angle

x-ray diffraction (WAXD) data and the bonding with

internal donors through Fourier-transform (FT)IR spectro-

scopy. Further, the structural features are correlated with

polymerization performance for propylene monomer.

Experimental Part

Preparation of Catalysts

For the catalyst synthesis, handling of air- and moisture-sensitive

materials was done using Schlenk line. Magnesium ethoxide was

treated with a mixture of titanium tetrachloride and chloroben-

zene in the presence of an internal donor at elevated temperature.

For catalyst-1 series, ethyl benzoate,[34] and for catalyst-2 series,

diisobutyl phthalate,[35] were used as internal donors. Further

treatment with a mixture of titanium tetrachloride and chlor-

obenzene was used, followed by isolation of solid catalyst after

hydrocarbon washing. For each internal donor, two set of catalyst

samples (A and B) with same synthetic methodology were

prepared, for analyzing reproducibility of composition (Table 1),

structural features, and propylene-polymerization performance

(Table 2 and 3).

Characterization of Catalysts

The titanium content in the catalysts was determined by

dissolving the catalyst in an acidic media and converting titanium

to Ti4þ by the addition of H2O2. UV–Vis spectra of the resultant

solution of peroxotitanium complexes were recorded using a

Perkin-Elmer UVLambda 35 spectrometer.

Nujol mull of catalysts were prepared and loaded on KBr discs

in a glove box, and transferred in air-tight containers to the FTIR

instrument. FTIR analysis was performed using a Perkin-Elmer

spectrum GX instrument, with 2cm�1 resolution and 32 scans

with flow of nitrogen.

WAXD measurements were carried using a Bruker AXS, D8

Advance X-ray diffractometer. The catalyst samples were placed

Table 1. Characteristics of synthesized MgCl2-supported titaniumcatalysts

Catalyst Lewis

Base

Analysis (wt-%)

Ti Cl Mg Lewis Base

1A EB 2.8 59 18.3 16.2

1B EB 2.9 61 18.1 15.8

2A DIBP 2.9 60 18.5 13.4

2B DIBP 2.7 61 18.2 12.8

DOI: 10.1002/macp.200800486

Influence of Internal Donors on the Performance and Structure of . . .

Table 2. Internal Donor–MgCl2 interaction: >C––O IR stretching band features

Catalyst Peak 1 Peak 2 Peak 3

n cmS1 Relative Amount n cmS1 Relative Amount n cmS1 Relative Amount

1A 1651 26% 1675 52% 1692 22%

1B 1650 25% 1675 52% 1691 23%

2A 1656 30% 1684 51% 1704 18%

2B 1655 31% 1685 51% 1705 19%

Table 3. MgCl2 structural features and productivity of catalysts

Catalyst Crystallite

width

Crystallite

thickness

Alpha/

beta ratio

Productivity Isotacticity

Index

(A) (A) (kgPP/gm Catalyst)

1A 31 32 1.4 4.4 95%

1B 30 27 1.2 4.5 94%

2A 47 33 2.1 7.0 96%

2B 43 30 2.0 6.8 95%

on the zero background, X-ray transparent, air-tight sample holder

in the glove box in nitrogen environment, so that measurements

could be performed in an inert atmosphere. The samples were

then transferred to the instrument. The step size in WAXD

measurements was 0.028, and the time per step was 12 s.

Component analysis was performed using TOPAS v3.0 software by

Bruker AXS.

Propylene Polymerization

Cocatalyst (triethyl aluminium) and catalyst were added to a

jacketed reactor containing hexane as solvent, so as to maintain a

Al:Ti 250:1 molar ratio. For series-1 catalysts, paraethoxy ethyl

benzoate was added as external donor in a 1:5 molar ratio with

respect to the cocatalyst. For series-2 catalysts, cyclohexylmethyl

dimethoxysilane was added as external donor, with 1:30 molar

ratio with respect to the cocatalyst. A propylene pressure of

5 kg cm�2 was maintained, and hydrogen was added as chain-

terminating agent. Polymerization was carried out for 1 h at 70 8C.

Afterwards polypropylene was isolated and vacuum dried.

Productivity of the catalysts was calculated from the polypropy-

lene yield (kg) to the catalyst amount (g), given in Table 3.

Polypropylene samples were extracted with boiling xylene in a

Soxlet apparatus. The isotacticity index (II) was measured as wt.-%

of xylene insoluble for each PP sample (Table 3).

Results and Discussion

The lateral cuts of MgCl2 matrix have predominantly three

types of Lewis-acid sites: five coordinated Mg ions on (104)

cuts (Mg#5), four coordinated Mg ions on (110) cuts (Mg#4),

and three coordinated Mg ions on edges or corners (Mg#3),



in comparison to six coordinated Mg ions in bulk (Figure 1).

The nomenclature proposed by Busico has been followed

for the discussion, considering the a-MgCl2 phase with four

coordinated Mg2þ ions on the (104) and five

coordinated Mg2þ ions on the (110) lateral cuts.[30] EB

and DIBP are Lewis bases, and can coordinate with Lewis

acidic sites on a MgCl2 matrix through the carbonyl

oxygen, which presents a high electron density.

Internal Donor–MgCl2 Interaction Studies

Internal donor–MgCl2 (>C––O—Mg2þ) complex formation

is best studied through FTIR spectroscopy, as the >C––O

stretching frequency is highly sensitive to the coordination

of oxygen atom with Mg ions. The stronger the coordina-

tion of >C––O with Mg, the weaker will the C––O bond be;

this is reflected in the FTIR spectrum, through shift in the

frequency of the >C––O stretching band to lower wave

numbers. The >C––O IR band, in case of catalysts, is very

complex, and to resolve it, deconvolution was performed

using a Gaussian-line-shape function. Assignments have

been performed based on literature,[36–38] on IR bands of EB

and DIBP with TiCl4, and on comparison of fitted IR bands

for EB and DIBP catalysts.

Complexes of EB

EB can bind to Mg2þ ions at (104) and (110) lateral cuts and

at edges or corners of MgCl2 crystallites. The order of

increasing >C––O coordination with various Mg sites is

Mg#5<Mg#4<Mg#3, which is the order of Lewis acidity,

www.mcp-journal.de 71


72

owing to the relative vacancies of Mg ions. The formation

of various complexes results in the shift of the >C––O

stretching frequency in EB, from 1720 cm�1 to a broad peak

with maxima at �1682 cm�1.

Figure 2 shows the IR spectrum of the >C––O stretching

band for catalyst 1A and 1B. For catalyst 1A, the IR band

has been deconvoluted to three bands, at 1651, 1675, and

1692 cm�1, as seen in Table 2, with Dn (>C––O)¼ 69, 45, and

28 cm�1, respectively. The position of the bands are in close

agreement with those reported by Potapov et al. for EB

complexes with Mg#3, Mg#4, and Mg#5 ions, respec-

tively.[37] Hence, the 1692 cm�1 band is attributed to Mg2þ

ions at (104) lateral cut, the 1675 cm�1 band to the (110)

cut, and the 1651 cm�1 band to the Mg2þ ions at corners

and edges. On comparing the distribution of intensities’

corresponding to the three fitted bands, determined from

deconvolution, it is evident that the EB-Mg#4 complex has

maximum intensity. The reason for this can be that Mg#4,

being a stronger Lewis acid than Mg#5, results in stronger

complex formation. The lower intensity for Mg#3 is due to

MgCl2 crystallites having less Mg2þ ions on corners or

edges than in (104) and (110) lateral cuts. A similar trend

was observed for Catalyst 1B (Table 2). Thus during

transformation of Mg(OEt)2 to MgCl2, EB exerts influence

on MgCl2-crystallite formation, leading to the preferential

formation of (110) and (104) lateral cuts. There was no IR

Figure 2. FTIR spectra of (a) catalyst 1A and (b) catalyst 1B, >C––Orange; Experimental band: thick dashed line, and fitted curves:thin lines.



band for the EB-TiCl4 adduct, as EB and TiCl4 form weak

complexes, leading to the preferential formation of the

more favorable EB-MgCl2 complexes.[36]

Complexes of DIBP

The >C––O stretching band shifts from 1728 cm�1 in DIBP

to a broad peak, centered at �1687 cm�1, in the catalyst.

The broad peak is representation of several superimposing

IR bands, corresponding to different complexes of DIBP

with MgCl2 and TiCl4. DIBP forms stable 1:1 complex with

TiCl4, where both >C––O groups chelate to Ti4þ ions,

completing the octahedral geometry around Ti and

providing stability to the complex having a >C––O

stretching band at 1647 cm�1.

DIBP can form different complexes with MgCl2, due to

chelation and bridging binding modes, and also DIBP

binding to Mg2þ ions at (104) and (110) lateral cuts and on

edges and corners. The deconvoluted bands at 1656, 1684,

and 1704 cm�1 (Table 2), shown in Figure 3a for Catalyst

2A, with Dn (>C––O)¼ 72, 44, and 24 cm�1, are indicative of

possibilities of formation of these several complexes.

The Dn (>C––O)¼ 44 and 24 cm�1 are comparative to Dn

(>C––O)¼ 45 and 28 cm�1 for EB–MgCl2 bonds at (110) and

(104) lateral cuts, respectively. Hence, the deconvoluted

bands at 1704 and 1684 cm�1 with 18% and 51%

Figure 3. FTIR spectra of (a) catalyst 2A and (b) catalyst 2B, >C––Orange; Experimental band: thick dashed line, and fitted curves:thin lines.

DOI: 10.1002/macp.200800486


Figure 4. MgCl2 matrix in (a) a-form having cubic packing and(b) b-form having hexagonal closed packing of Cl–Mg–Cl triplelayers. Dark gray and light gray spheres correspond to thechlorine and magnesium ions, respectively.

Figure 5. (a) WAXD of catalyst 1A, planes corresponding to a-formhaving ccp have been indicated by the subscript ‘c’ and planescorresponding to b-form having hcp have been indicated by thesubscript ‘h’. (b) Deconvoluted WAXD pattern of catalyst 1B,dotted line corresponds to the experimental pattern, thin linecorresponds to the individual fitted peaks, and thick line corre-sponds to the fitted pattern.

intensities can be assigned to the DIBP-bridge complexes

with Mg#5 (104) and Mg#4 (110), respectively. DIBP is also

able to form chelate bonds with Mg2þ ion on the (110)

plane, and the IR band of this complex will contribute to

the 1704 cm�1 band.[38]

The deconvoluted band at 1656 cm�1 has Dn (>C––O) of

72 cm�1, in comparison to 69 cm�1 for the EB–Mg#3

complex, and has higher intensity (�30%) in comparison to

the EB–Mg#3 complex (�25%, Table 2). The deconvoluted

band at 1656 cm�1 can be assigned to the overlapping

>C––O bands of DIBP–Mg#3 and DIBP–TiCl4 complexes. The

band at higher frequency, at 1758 cm�1, is due to the

complex between MgCl2 and –COCl species, which is

formed during catalyst synthesis at high temperatures.

Catalyst 2B shows similar behavior, indicating identical

bonding patterns.

Comparison of EB and DIBP interactions with MgCl2

indicate similar behaviors for both internal donors. The

internal donors are binding predominantly to the two

types of MgCl2 lateral cuts, (104) and (110), thereby

assisting in their formation during catalyst synthesis.

Andoni et al. reported a similar observation on the basis of

controlled MgCl2-crystallite growth, with absorption of

TiCl4 and internal donors followed by ethylene polymer-

ization studied through SEM and AFM.[27]

MgCl2 Structural Studies

MgCl2 exists as two crystalline forms, a-form and b-

form.[19,20,39,40] The common a-form of MgCl2 is character-

ized by a distorted cubic packing (ccp) of Cl atoms (. . ..ABC

ABC ABC. . ..). The b-form of MgCl2 is characterized by a

hexagonal close packing (hcp) of Cl atoms (. . ..AB AB

AB. . ..). MgCl2 in a-form and b-form exhibit layered

structures, with two outer Cl atoms sandwiching a single

plane of Mg atoms, termed Cl–Mg–Cl triple layers, as

depicted in Figure 4. The transformation of MgCl2 to active

catalyst results in different phases, namely the a-form, b-

form, and d-form of MgCl2. The influence of EB and DIBP on

the structure of MgCl2 has been studied through WAXD.

Influence of EB on MgCl2 Structure

WAXD of catalyst 1A and 1B are shown in Figure 5. WAXD

peaks of thea-form andb-form of MgCl2 have been obtained

from the PDF files 01-089-1567 and 01-072-1517, respec-

tively, and further supported by an analysis reported by

Chien et al.[39,40] WAXD data presented the following

features: 1) 2u 9–188: broad peak, 2) 2u 218: broad halo,

3) 2u 27–388: broad peak, 4) 2u 438: broad halo, 5) 2u 48–548:broad peak, and 6) 2u 57–678: broad halo. Deconvolution

using TOPAS enabled the comprehensive analysis of the

WAXD, as shown in Figure 5b.

WAXD deconvolution for catalyst 1A and 1B in the 9–

188 2u range resulted in three peaks, at around 11.3, 13.2,


� 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mcp-journal.de 73


Figure 6. (a) WAXD of catalyst 2A, planes corresponding to a-formhaving ccp have been indicated by the subscript ‘c’ and planescorresponding to b-form having hcp have been indicated by thesubscript ‘h’. (b) Deconvoluted WAXD pattern of catalyst 2B,dotted, thin, and thick lines correspond to experimental pattern,individual fitted peaks, and the fitted pattern, respectively.

74

and 15.98. The peak at 15.98corresponds to the (003) plane

of the a-MgCl2 phase and the (001) of the b-MgCl2 phase.

The peaks at 11.3 and 13.28, which are absent in the a-

MgCl2 or the b-MgCl2 phase, emerge due to the distortion

in the MgCl2 structure. This can be attributed to the

changes in the regular arrangement of Cl–Mg–Cl triple

layers in the a-MgCl2 or the b-MgCl2 phases. This increased

interlayer distance might be due to the intercalation by the

donors. Crystallite thickness as calculated from the over-

lapped (003) or (001) diffraction peaks from a-MgCl2 or b-

MgCl2 phases, respectively, is 32 A.

The broad peak in the range of 27–388can be fitted to

three peaks, at 30.0, 32.0, and 34.98. The peak at

30.08corresponds to the overlap of the peaks from the

(012) and (006) planes of a-MgCl2 and the (002) plane of the

b-MgCl2. The broad peak at 32.08 is from the diffraction of

the (011) plane of b-MgCl2. The broad peak at 34.98 is the

diffraction peak of the (104) plane of a-MgCl2. Thus, the

deconvoluted peaks at 32.0 and 34.98 can be analyzed to

understand the relative b-MgCl2 and a-MgCl2 phase

distributions in the catalysts. Ratio of the intensities of

34.9 and 32.08 peaks, corresponding to relative a-MgCl2

and b-MgCl2 phases concentrations, is 1.4. The broad peak

at 50.28 is attributed to the (110) planes of a-MgCl2 and b-

MgCl2, and to the (018) plane of a-MgCl2 phase. The

crystallite width, calculated from the diffraction peak at

50.28, is 31 A. Component analysis reveals similar MgCl2

structural features for catalyst 1A and 1B, as shown in

Table 3.

Influence of DIBP on MgCl2 Structure

Figure 6 shows the WAXD of catalyst 2A and 2B, with the

following features: 1) 9–188: broad peak, 2) 218: broad halo,

3) 27–388: broad peak, 4) 438: broad halo, 5) 48–548: broad

peak, and 6) 57–678: broad halo. Deconvolution enabled

the comprehensive analysis of the WAXD, and highlighted

the differences in the WAXD profiles of EB and DIBP

catalysts. Deconvoluted WAXD of the catalyst 2B is given

in Figure 4b.

WAXD deconvolution in the 9–188 range, similar to the

catalyst 1B, resulted in three peaks, at around 11.1, 13.5,

and 15.98. The analysis is made on the same lines as that of

the catalyst 1B. Crystallite thickness, calculated from the

overlapped (003) or (001) diffraction peaks from a-MgCl2 or

the b-MgCl2 phases, respectively, is 33 A. Crystallite width

calculated from the diffraction peak at 50.38 is 47 A.

Three peaks at 29.9, 32.0, and 34.78 were deconvoluted

from the broad peak in the range of 27–388. The difference

in this region between catalyst 1B and catalyst 2B is

significant. The peaks at 32.0 and 34.98, attributed to the

(011) plane of b-MgCl2 and the (104) plane of a-MgCl2,

respectively, have changes in the intensities. The monoe-

ster catalyst 1B has a more intense fitted peak at 32.08 in



comparison to dialkyl phthalate catalyst 2B. The deconvo-

luted peak at 34.98, corresponding to the (104) plane of a-

MgCl2, is more intense in catalyst 2B. The ratio of the

intensities of the 34.9 and 32.08 peaks, corresponding to

relative a-MgCl2 and b-MgCl2 phase concentrations, is 2.0,

in comparison to 1.4 for catalyst 1B. This difference

indicates that catalyst 1B has higher b-MgCl2 phase or hcp

packing of MgCl2 triple layers in comparison to catalyst 2B.

DIBP catalysts have higher a-MgCl2 phase concentrations;

or in comparison to EB catalysts, more MgCl2 triple layers

have ccp packing (Table 3).

These observations indicate that there are phase

distribution differences in the MgCl2 matrix of EB and

DIBP catalysts, while both the catalysts have been

prepared using same Mg(OEt)2 precursor. The only

difference is the structure of donors, EB being mono-

dentate and DIBP being bidentate. The observation of

differences in the distribution of a-MgCl2 and the b-MgCl2

may be interpreted in terms of the starting material, that

is, Mg(OEt)2 first get converted to more thermodynami-

cally stable a-MgCl2 phase, which during catalyst-pre-

paration process is transformed into b-MgCl2 and d-MgCl2

phases. During these transformations, DIBP binds to

adjacent MgCl2 layers (Figure 7), and provides stability

to the a-MgCl2 phase, preventing further phase changes.

DOI: 10.1002/macp.200800486


Figure 7. (110) Zip coordination mode of bidentate dialkyl phthalate donor with mag-nesium ions along the (110) plane. Dark gray and light gray spheres correspond to thechlorine and magnesium ions, respectively.

While in the case of EB, in the absence of interlayer

bridging, phase changes are more facile, leading to

relatively higher b-MgCl2 phase content in comparison

to DIBP-based catalysts. This may be the reason for higher

crystallite width of �45 A for DIBP-based catalysts in

comparison to �30A for EB-based catalysts. The final

catalyst thus contains both a-MgCl2 and b-MgCl2 phases,

along with d-MgCl2 phase. Recently, based on DFT

calculations, Correa et al. reported that diethyl phthalate

is capable of forming coordination bonds to Mg atoms on

the adjacent layers, and named this binding mode (110) zip

coordination mode.[15]

Propylene Polymerization Performance

EB- and DIBP-based catalysts were evaluated for propy-

lene-polymerization performance at high pressure

(Table 3). The EB-based catalyst systems showed produc-

tivity in the range of 4.5 kg PP g�1 catalyst, with �95%

isotacticity index. DIBP-based catalysts showed higher

productivity, in the range of 6.9 kg PP g�1 catalyst, with

�95% isotacticity index. The DIBP-based catalysts showed

�55% higher productivity in comparison to EB-based

catalysts, with similar isotacticity index of �95%. The

probable reason for higher productivity for DIBP catalysts

is that DIBP is binding to the adjacent MgCl2 layers on (110)

lateral cuts, and is able to hold the layers during propylene

polymerization. This may provide protection to (110)

lateral cuts during polymerization, leading to higher

catalytic productivity.



Conclusion

MgCl2-supported high-performance tita-

nium catalyst systems have complex

structural aspects. FTIR studies indicate

that the internal donors EB and DIBP

impart influence on the formation of

MgCl2-crystallite lateral cuts, with higher

preference for (110) over (104) lateral cuts.

The MgCl2 matrix is formed during

catalyst preparation from Mg(OEt)2, and

is characterized by the presence of a-

MgCl2, b-MgCl2, and disordered d-MgCl2

phases. The bidentate dialkyl phthalate

donor holds the adjacent MgCl2 layers by

interlayer binding and (110) zip coordina-

tion, and even stabilizes the same layer via

bridging. This in turn may stabilize

the MgCl2 crystallites, and hence the

active sites, during several physical and

chemical process occurring during poly-

merization, leading to substantially high

productivity of phthalate catalysts in com-

parison to the ethyl benzoate catalysts.

Received: October 3, 2008; Accepted: October 30, 2008; DOI:10.1002/macp.200800486

Keywords: internal donor; magnesium chloride; polypropylene;wide-angle X-ray diffraction; Ziegler-Natta catalysts

[1] P. Galli, Macromol. Symp. 1995, 89, 11.[2] V. K. Gupta, J. Polym. Mater. 1999, 16, 97.[3] J. C. Chadwick, Macromol. Symp. 2001, 173, 21.[4] H. N. Cheng, Macromol. Theory Simul. 1993, 2, 901.[5] L. Cavallo, G. Guerra, P. Corradini, J. Am. Chem. Soc. 1998, 120,

2428.[6] V. Busico, R. Cipullo, G. Monaco, M. Vacatello, A. L. Segre,

Macromolecules 1997, 30, 6251.[7] V. Busico, R. Cipullo, Prog. Polym. Sci. 2001, 26, 443.[8] J. C. Chadwick, F. P. T. J. van der Burgt, S. Rastogi, V. Busico, R.

Cipullo, G. Talarico, J. J. R. Heere, Macromolecules 2004, 37,9722.

[9] S. H. Kim, G. A. Somorjai, J. Phys. Chem. B 2001, 105, 3922.[10] P. Galli, G. Vecellio, J. Polym. Sci. A. Polym. Chem. 2004, 42, 396.[11] P. Corradini, J. Polym. Sci. A. Polym. Chem. 2004, 42, 391.[12] P. Corradini, Macromol. Symp. 1995, 89, 1.[13] D. Ribour, V. Monteil, R. Spitz, J Polym. Sci. A. Polym Chem.

2008, 46, 5461.[14] D. A. Trubitsyn, V. A. Zakharov, I. I. Zakharov, J. Mol. Catal. A.

Chem. 2007, 270, 164.[15] A. Correa, F. Piemontesi, G. Morini, L. Cavallo, Macromolecules

2007, 40, 9181.[16] G. Monaco, M. Toto, G. Guerra, P. Corradini, L. Cavallo, J. Phy.

Chem. C 2000, 33, 8953.[17] H.-L. Ronkko, H. Knuuttila, P. Denifl, T. Leinonen, T. Venalai-

nen, J. Mol. Catal. A. Chem. 2007, 278, 127.

www.mcp-journal.de 75


76

[18] M. Chang, X. Liu, P. J. Nelson, G. R. Munzing, T. A. Gegan, Y. V.Kissin, J. Catal. 2006, 239, 347.

[19] M. Vittadello, P. E. Stallworth, F. M. Alamgir, S. Suarez, S.Abbrent, C. M. Drain, V. D. Noto, S. G. Greenbaum, Inorg. Chim.Acta 2006, 359, 2513.

[20] M. L. Ferreira, D. E. Damiani, J. Polym. Sci. A. Polym. Chem.1994, 32, 1137.

[21] V. D. Noto, S. Bresadola, Macromol. Chem. Phys. 1996, 197, 3827.[22] V. D. Noto, D. Fregonese, A. Marigo, S. Bresadola, Macromol.

Chem. Phys. 1998, 199, 633.[23] A. Marigo, C. Marega, R. Zannetti, G. Morini, G. Ferrera, Eur.

Polym. J. 2000, 36, 1921.[24] A. Andoni, J. C. Chadwick, S. Milani, H. J. W. Niemantsverdriet,

P. C. Thune, J. Catal. 2007, 247, 129.[25] A. Andoni, J. C. Chadwick, H. J. W. Niemantsverdriet, P. C.

Thune, Macromol. Rapid Commun. 2007, 28, 1466.[26] A. Andoni, J. C. Chadwick, H. J. W. Niemantsverdriet, P. C.

Thune, Macromol. Symp. 2007, 260, 140.[27] A. Andoni, J. C. Chadwick, H. J. W. Niemantsverdriet, P. C.

Thune, J. Catal. 2008, 257, 81.[28] H. Mori, M. Sawada, T. Higuchi, K. Hasebe, N. Otsuka, M.

Terano, Macromol. Rapid Commun. 1999, 20, 245.[29] U. Giannini, Makmol. Chem. Suppl. 1981, 5, 216.



[30] V. Busico, M. Causa, R. Cipullo, R. Credendino, F. Cutillo, N.Friederichs, R. Lamanna, A. Segre, V. V. A. Castelli, J. Phys.Chem. C 2008, 112, 1081.

[31] M. Boero, M. Parrinello, H. Weiss, S. Huffer, J. Phys. Chem. A2001, 105, 5096.

[32] M. Seth, P. M. Margl, T. Ziegler, Macromolecules 2002, 35,7815.

[33] L. Brambilla, G. Zerbi, F. Piemontesi, S. Nascetti, G. Morini,J. Mol. Catal. A. Chem. 2007, 263, 103.

[34] V. K. Kaushik, V. K. Gupta, D. G. Naik, Appl. Surf. Sci. 2006, 253,753.

[35] V. K. Gupta, S. Satish, I. S. Bhardwaj, J. Macromol. Sci Pure Appl.Chem. A 1994, 31, 451.

[36] C. B. Yang, C. C. Hsu, Y. S. Park, H. F. Shurvell, Eur. Polym. J.1994, 30, 205.

[37] A. G. Potapov, G. D. Bukatov, V. A. Zakharov, J. Mol. Catal. A.Chem. 2006, 246, 248.

[38] Y. V. Kissin, X. Liu, D. J. Pollick, N. L. Brungard, M. Chang, J. Mol.Catal. A. Chem. 2008, 287, 44.

[39] Y. Hu, J. C. W. Chien, J. Polym. Sci. A. Polym. Chem. 1988, 26,2003.

[40] J. C. W. Chein, J. C. Wu, C. I. Kuo, J. Polym. Sci. A. Polym. Chem.1983, 21, 737.

DOI: 10.1002/macp.200800486

Documents

Influence of Internal Donors on the Performance and Structure of MgCl2 Supported Titanium Catalysts for Propylene Polymerization