Polymer Synthesis CHEM 421 Chemical Review 2000, Issue 4 “FRONTIERS IN METAL-CATALYZED POLYMERIZATION” Also Angew. Chem. Int. Ed. 1999, 38, 428 ± 447

Polymer Synthesis CHEM 421 Soluble Metallocene Cataysts Used a mixture of meso and racemic ansa-titanocenes –Stereo-rigid –Ethylene-bridged –Rac: chiral with C 2 -symmetric axis –Meso: achiral

Polymer Synthesis CHEM 421

Polymer Synthesis CHEM 421

Polymer Synthesis CHEM 421 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

Polymer Synthesis CHEM 421 Physical Properties of Polypropylene

Polymer Synthesis CHEM 421 Olefin Polymerizations with Early Metal Catalysts Metallocene Catalysts: Technological advance A) Incremental B) Major: 1) New Materials 2) Detailed mechanistic understanding Not a black box anymore… ~ 2 × lbs/year polyethylenes(PE), polypropylenes(PP) produced worldwide!

Polymer Synthesis CHEM 421 Olefin Polymerizations with Early Metal Catalysts 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

Polymer Synthesis CHEM 421 Metallocene Catalysts 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 Topaz TM (T g = 140 – 200 °C)

Polymer Synthesis CHEM 421 Late vs Early Transition Metal Catalysts 1. Less oxophilic ― improved functional group tolerance 2. Rapid β-elimination ― chain transfer competitive with propagation dimers, oligomers 3. Generally, lower activities

Polymer Synthesis CHEM 421 Late Metal Catalysts Not useful…β-elimination Propagation Β-Elimination Dissociation Displacement

Polymer Synthesis CHEM 421 Chain Transfer Mechanisms

Polymer Synthesis CHEM 421 Chain Transfer Mechanisms

Polymer Synthesis CHEM 421 Blocking of Axial Coordination Sites

Polymer Synthesis CHEM 421 α–Diimine Based Catalysts ■ 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

Polymer Synthesis CHEM 421 Mechanistic Model

Polymer Synthesis CHEM 421 Polyethylene

Polymer Synthesis CHEM 421 Poly (α–Olefins)

Polymer Synthesis CHEM 421 Commercial Copolymers of Ethylene and Polar Vinyl Monomers ● Radical Initiation ● High temperatures, very high ethylene pressure