Transcript Polymer Synthesis CHEM 421

Polymer Synthesis
CHEM 421
Chemical Review 2000, Issue 4
“FRONTIERS IN METAL-CATALYZED
POLYMERIZATION”
Also
Angew. Chem. Int. Ed. 1999, 38, 428 ± 447
Soluble Metallocene Cataysts
Polymer Synthesis
CHEM 421
• Used a mixture of meso and racemic ansa-titanocenes
– Stereo-rigid
– Ethylene-bridged
– Rac: chiral with C2-symmetric axis
– Meso: achiral
Polymer Synthesis
CHEM 421
Polymer Synthesis
CHEM 421
Polymer Synthesis
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• Unbridged metallocene catalysts
• Rapid isomerization, low barriers
• What kind of polymer is produced?
–Atactic Polymer
Polymer Synthesis
CHEM 421
• Unbridged metallocene catalysts
• Added phenyl group to indene
– Inhibits rate of ligand rotation
Polymer Synthesis
CHEM 421
Polymer Synthesis
CHEM 421
• Unbridged metallocene catalysts
• Added phenyl group to indene
Polymer Synthesis
CHEM 421
Physical Properties of
Polypropylene
Polymer Synthesis
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Olefin Polymerizations with Early Metal
Catalysts
Polymer Synthesis
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~ 2 × 1011 lbs/year polyethylenes(PE), polypropylenes(PP) produced worldwide!
Metallocene Catalysts:
Technological advance
A) Incremental
B) Major:
1) New Materials
2) Detailed mechanistic understanding
Not a black box anymore…
Olefin Polymerizations with Early Metal
Catalysts
Polymer Synthesis
CHEM 421
Metallocene Catalysts:
Incremental technological advance
● Increased activities/productivities
● Many different grades of ethylene/ α-olefin copolymers
● Control of MW, MWD
bimodal, unimodal, PDI < 5.0!
Existing markets are being extended into new applications
Metallocene Catalysts
Polymer Synthesis
CHEM 421
• Major Technological Advance
–New Materials
» Syndiotactic polystyrene
»Tm = 270 °C, 40-50% X-tal w/ good rate of
x-tallization
» Syndiotactic and elastomeric PP
» Cyclic Olefin Copolymers
»Hoechst’s TopazTM (Tg = 140 – 200 °C)
Late vs Early Transition
Metal Catalysts
Polymer Synthesis
CHEM 421
1. Less oxophilic ― improved functional group tolerance
2. Rapid β-elimination ― chain transfer competitive with
propagation
dimers, oligomers
3. Generally, lower activities
Late Metal Catalysts
• Not useful…β-elimination
Propagation
Dissociation
-Elimination
Displacement
Polymer Synthesis
CHEM 421
Chain Transfer Mechanisms
Polymer Synthesis
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Chain Transfer Mechanisms
Polymer Synthesis
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Blocking of Axial Coordination Sites
Polymer Synthesis
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α–Diimine Based Catalysts
Polymer Synthesis
CHEM 421
■ High molecular weight polymers with unique microstructures from:
● ethylene
● α – olefins
● cyclopentene
● trans-1,2-disubstituted olefins
■ Copolymers of ethylene with certain polar vinyl monomers
Mechanistic Model
Polymer Synthesis
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Polyethylene
Polymer Synthesis
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Poly (α–Olefins)
Polymer Synthesis
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Commercial Copolymers of Ethylene
and Polar Vinyl Monomers
Polymer Synthesis
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● Radical Initiation
● High temperatures, very high ethylene pressure