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Chap 12. Zieglar-Natta Catalyst

- Before Z-N Catalyst invention, PP composites were only atactic form - After that, isotactic PP composites of extraordinary MW(>106) is synthesized

LDPE = HPPE HDPE PP

This has less hardness, stiffness and strength compared to HDPE, but better ductility, Free radical

10 billion lb/yr

Use chromium compounds.

Zieglar-Natta process is recent application.

A few number of branches

AlR3, AlHR2

Natta

4 billion lb/yr

Characteristic conditions for PP

PP and solid catalysts are put together at 50 to 90 below 5atm.℃ ℃After stopping of reaction, it is washed with H2O or ROH to remove the catalysts.MW is on the control of chain transfer agent

E.g.) CO2, O2, H2, H2O, …

Zieglar-Natta Catalyst

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Dr. Ziegler and Dr. Natta

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Assumption: equal site reactivity

TiCl

Cl

ClCl

*

CH2

CH2=CHCH3+ TiCl

Cl

ClCl

*

CH2

CHCH3

CH2

TiCl

Cl

ClCl

*

CH2

HC CH3

Ti

CH2 CHCH3

CH2Ti

*

CH2CHCH3

CH2

open

isotactic syndio

migration

- Monometallic Corsee mechanism

TiCl

Cl

Cl Cl*

open

CH2=CHCH3

MonometallicBimetallic mechanism

Zieglar-Natta Catalyst

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Ti

CH2

AlR

CHCH3CH2

Ti AlR

CH2

CHCH3

H2C

Ti AlR

CH2

CHCH3

H2C

TiCH

AlR

CHCH3

CH2

β-TiCl3

1 vacancy site => isotactic

2 vacancy sites => atactic 1 vacancy site => isotactic

Bimetallic

TiCl

Zieglar-Natta Catalyst

α-TiCl3

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Zieglar-Natta Catalyst

This image shows the mechanism by which the Ziegler Natta catalyst polymerizes 1-propene. The image was created by Christine Ann.

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Polymerization rate

Time

Types of rate curves observed in Ziegler-Natta polymerization: (A) constant; (B) decaying; and (C) decaying to constant

A

B

C

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A

B

CD

E

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Chap 13. Polymerization Processes

Homogeneous polymerization

Heterogeneous polymerization

Bulk polymerization

Solution Polymerization

Suspension polymerization

Emulsion polymerization

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Bulk polymerization

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Solution Polymerization

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Suspension polymerization

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Emulsion polymerization

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Stages in Emulsion Polymerization