Polymer Chemistry

Guangxi University School of Chemistry & Chemical Engineerin

g

Li Guang Hua (李光华)

Lab：材料楼—409#，321# E-mail : lighua@gmail.comCell phone: 15978133590

CHAPTER 5

1. Introduction

Coordination Polymerization:

2. Heterogeneous Ziegler-Natta Polymerization2.1 Heterogeneous Catalysts2.2 Polymerization of α-olefin2.3 Polymerization of Diene

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2.3 Polymerization of Diene

3. Homogeneous Ziegler-Natta Polymerization3.1 Metallocene Catalysts3.2 Mechanism

4. Supported Metal Oxide Catalysts

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1. INTRODUCTION (I)

CH2 CH2n CH2 CH2 nR PZN

High T & Plow density PE (LDPE)

CH2 CH

CH3

n R PZNor ionic PZN

Oligomer

Both ethylene and propylene are polymerizable monomers

(branched structure)

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Both ethylene and propylene are polymerizable monomers thermodynamically.

In 1953, Karl Ziegler (GER) discoveredØ

CH2 CH2n + Al(C2H5)3 TiCl4 CH2 CH2 nlow T & P

high density PE (HDPE)(linear structure)

catalystcocatalyst

In 1954, Giulio Natta (ITA) discoveredØ

CH2 CHn + Al(C2H5)3 TiCl3CH3

CH2 CH nCH3

low T & P

isotactic PP (i-PP)catalystcocatalyst

1. INTRODUCTION (II)

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In 1959, Natta proposed bimetallic mechanism.

In 1960, Cossee-Arlman proposed monometallic mechanism.

Monometallic mechanism is favored in heterogeneous processes.

1. INTRODUCTION (III)

TiR

RAl

Ø Bimetallic mechanism (1959)

Active speciesCH2 CH

X

TiR

RAl

δδ

δ δ

TiR

RAl

CH2 CH

X

CH2=CHX

coordination complexation

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Ti RR Al

CH2 CH

X

Six-membered cyclictransition state

TiR

Al

R

CH2

CH X

δδ

TiR

Al

R

CH2

CH X

Insertion to Al-C bond

1. INTRODUCTION (IV)

Ø Monometallic mechanism (1960)

Active species

CH2=CHX

Coordination Four-membered cyclictransition state

Ti

R

ClCl

Cl

ClTi

R

ClCl Cl

Cl C

C

H H

X H

Ti

R

ClCl Cl

Cl C

C

H H

X H

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transition state

Insertion to Ti-C bond

Ti

R

ClCl Cl

ClCH2

CH

XTi

R

ClCl Cl

ClCH2

CH X

migration of the chain

Ti

R

ClCl Cl

Cl C

C

H H

X H

1. INTRODUCTION (V)

TiR

RAl

CH2 CH

X

Coordination

Determine to insert the direction of monomers

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Stereoregular polymer (立构规整聚合物)

Coordination PZN or complexing PZN Insertion PZN orStereoregular PZN (定向聚合)

â Ziegler and Natta shared the Nobel Prize in Chemistry in 1963.

1. INTRODUCTION (VI)

Feature of coordination PZN:

¹ Reaction is of anionic nature

¹ Monomer coordinates with a transition metal to form σ-πcomplex

¹ Polymer chain grows by successive insertion reactionsof complex monomers

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¹ Can form stereoregular polymers (but also atactic polymers)

Heterogeneous PZNHomogeneous PZNCoordination PZN

2. HETEROGENEOUS Z-N PZN (I)

Heterogeneous catalystsFZiegler-Natta catalyst :

IV ~ VIII transition metal compound

IA ~ IIIA organometallic compound

(catalyst)

(cocatalyst)

ex., Ti, V, Cr, Mn, Fe, Co, Nipost transition metal

Ø

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IA ~ IIIA organometallic compoundex., AlR3, AlR2X

TiCl4 + AlR3 R3AlCl TiCl3Provide vacant sites

TiCl3 + AlR3

α, δ,γ, and β form

High degree of stereoregularityAtactic polymer

Catalyst Stereoregularity (%)

AlEt3 + TiCl4 35AlEt3 + β-TiCl3 45AlEt + α-TiCl 85

Variation of polypropylene isotacticity with catalyst

PZN of α-olefinsF

2. HETEROGENEOUS Z-N PZN (II)

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AlEt3 + α-TiCl3 85AlEt3 + ZrCl4 55AlEt3 + VCl3 73AlEt2X + TiCl3 90–99AlEtX2 + γ-TiCl3 +amine 99

Two components

Three components

Lewis base(Electron donor)

2AlEtX2 + NR3 AlEt2X + NR3AlX3

¹ First generation catalysts of PP (1950s-60s)

Catalyst Stereoregularity (%) Efficiency (g PP/g Ti)

AlEt3 + α-TiCl3 85 5×103

¹ Second generation catalysts of PP (1960s)

2. HETEROGENEOUS Z-N PZN (III)

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Catalyst Stereoregularity(%)

Efficiency (g PP/g Ti)

AlEt3 + α-TiCl3 + HMPTA ~ 90 5×104

HMPTA : hexamethylphosphorictriamide (六甲基磷酰三胺)

P[N(CH3)2]3=O

¹ Third generation catalysts of PP (1970s-80s)

Catalyst Stereoregularity(%)

Efficiency (g PP/g Ti)

AlEt3 + α-TiCl3 + esterssupported on MgCl2

> 98 2.4×106

2. HETEROGENEOUS Z-N PZN (IV)

MgCl2

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Eliminated the need for the costly step of removing catalyst from the product.

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••••

••••••••

•

•••••

••••

TiCl3-AlEt3

Supported catalyst

CH2 = CH2 > CH2 = CHCH3 > CH2 = CHCH2CH3

> CH2 = CHCH2CH(CH3)2 > CH2 = CHCH(CH3)2

> CH = CHCH(CH CH ) > CH = CHC(CH )

Monomer (1-alkene) activity decreases with increasing steric hindrance about the double bond.

Monomer ReactivityØ

2. HETEROGENEOUS Z-N PZN (V)

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> CH2 = CHCH(CH2CH3) > CH2 = CHC(CH3)3

MW and MWDØ

¹ MW would, in most instances, be too high for commercial use.

Chain transfer agents are used to control MW.

Termination of chain growth may occur a number of ways, leading to both saturated and unsaturated chain ends. Saturated chain ends are normally more prevalent in Z-N polymers.

Ti CH2CH2R

R+ CH2 C

Ti + CH CHCH CHR

CH2 CHR

CH2 CHR

2. HETEROGENEOUS Z-N PZN (VI)

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Ti CH2CHR

TiR

+ CH3CHCH CHR

Ti H + CH2 CR

Ti R' +R

CH2CHR'2Al

Ti H +R

CH3CH

AlR'3

H2

CH2 CHR

Mw/Mn > 5 ~ 6

¹ Molecular weight distributions are generally broader when insoluble catalysts are used than soluble catalysts.

The broad distribution may arise from :

2. HETEROGENEOUS Z-N PZN (VII)

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The decay of catalyst activity

The presence of sites of variable activity

¤ Reduce the number or activity of active centers

¤ Encapsulation of active centers by polymer, which prevents approach by monomer

2. HETEROGENEOUS Z-N PZN (VIII)

PZN of DieneF

Catalysts for the Stereospecific Polymerization of Butadiene

Catalyst Yield (%) Polymer structure

R3Al + VCl4 97−98 trans-1,4R3Al + VCl3 99 trans-1,4R Al + VOCl 97−98 trans-1,4

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R3Al + VOCl3 97−98 trans-1,4R3Al + TiI4 93−94 cis-1,4R2AlCl + CoCl2 96−97 cis-1,4R3Al + Ti(OC6H9)4 90−100 1,2Et3Al + Cr(C6H5CN)4

Al/Cr = 2 ∼ 100 syndiotactic-1,2Al/Cr = 10 ∼ 100 isotactic-1,2

2. HETEROGENEOUS Z-N PZN (IX)

Catalysts for the Stereospecific Polymerization of Isoprene

Catalyst Yield (%) Polymer structure

R3Al + α-TiCl3 91 trans-1,4Et3Al + VCl3 99 trans-1,4Et Al + TiCl 97−98 trans-1,4

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Et3Al + TiCl4 97−98 trans-1,4Al/Ti < 1 95 trans-1,4Al/Ti > 1 96 cis-1,4

Et3Al + Ti(OR)4 95 3,4

3. HOMOGENEOUS Z-N PZN (I)

Metallocene catalysts (茂金属催化剂)FMetallocene catalysts were discovered by Kaminsky late in the 1970s.

TiCl

Cl+ R2AlCl

CH2 CH

CH

CH2 CH2 Low catalytic activity

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CH3 Unreactivebis(cyclopentadienyl) titanium dichloride (Cp2TiCl2)

AlMe3 methylaluminoxanes (MAO)hydrolysis

TiCl

Cl+ MAO High activity for alkene

Low tacticitycocatalyst

3. HOMOGENEOUS Z-N PZN (II)

MAO (methylaluminoxanes)Ø

¹ MW = 1000 ~ 1500

¹ Two proposed structures

CH3

Al

CH3

O

CH3

Al

CH3

O

CH3

Al

CH3

O

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CH3

Al

CH3

O

CH3

Al

CH3

O

CH3

Al

CH3

O

CH3

CH3

Al O Al

CH3

O AlCH3

CH3n

¹ Expensive

3. HOMOGENEOUS Z-N PZN (III)

Metallocene catalystsØ

Z

R R

RR

MX

X

M : Zr, Ti, or Hf

X : Cl or alkyl

R : H or alkylZ : bridging group

C(CH ) , Si(CH ) , or CH CH

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RR C(CH3)2, Si(CH3)2, or CH2CH2

ZrCl2(CH3)2Si ZrCl2(CH3)2C

Me2Si(Ind)2ZrCl2 Me2C(Flu)(Cp)ZrCl2

3. HOMOGENEOUS Z-N PZN (IV)

MechanismF

ZrCH3

CH3

L

L+

CH3

CH3

Al O Al(CH3)O

Al(CH )O

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ZrCH3

L

L

O Al(CH3)Oδ

δ+ Al(CH3)3Zr

CH3 CH3

LL Zr

CH3

CH3

O

Al(CH3)O

Formation of active site(single-site)

ZrCH2

L

L

δ

δ

O

CH2

CH2 CH2

AlO

O

3. HOMOGENEOUS Z-N PZN (V)

ZrCH2

L

L

δ

δO

CH2

AlO

O

CH CH

Possible PZN mechanism for ethylene

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CH2 CH2CH2 CH2

Zr

CH2

L

L

δ

δO

CH2

CH2CH2

AlO

O

3. HOMOGENEOUS Z-N PZN (VI)

Features of metallocene catalystsØ

¹ High catalytic activity (homogeneous system)

10 to 100 times higher than conventional Z-N catalysts

¹ Single-site feature

Ex., Cp2ZrCl2/MAO for ethylene PZN : 108 g(PE)/(g Zr•h)

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¹ Single-site feature

Narrow MWD : 2 ~ 2.5MWD of conventional Z-N catalyst : 5 ~ 6

¹ Altering the structure of metallocene catalysts may control the MW, MWD, and stereoregularity of polymers.

LLDPE, HDPE, i-PP, s-PP, s-PS, etc.

4. SUPPORTED METAL OXIDE CATALYSTS (I)

Phillips petroleum company: Phillips catalyst

OO

O

Cr

Si Si+ 2H CH O

OO

O

Cr

Si Si+ CH 2

OO

CH 2

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Metal : Cr, V, Mo, Ni, Co, W, Ti, etc.

Apply to the production of HDPE, LLDPE.

Support : Silica, alumina, charcoal, etc.

¹ Activities of Phillips catalysts are less than Z-N catalyst.

¹ Stereoregularity of Phillips catalysts is less than Z-N catalyst.

Karl Ziegler (1898－1973)

Giulio Natta (1903 ~ 1979)

COORDINATION PZN

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H.W. :Review exercises: 1, 4 and 5