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Chemical Review 2000, Issue 4 “FRONTIERS IN METAL-CATALYZED POLYMERIZATION” Also

Chemical Review 2000, Issue 4 “FRONTIERS IN METAL-CATALYZED POLYMERIZATION” Also Angew. Chem. Int. Ed. 1999, 38, 428 ± 447. Soluble Metallocene Cataysts. Used a mixture of meso and racemic ansa -titanocenes Stereo-rigid Ethylene-bridged Rac: chiral with C 2 -symmetric axis

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Chemical Review 2000, Issue 4 “FRONTIERS IN METAL-CATALYZED POLYMERIZATION” Also

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

  2. Soluble Metallocene Cataysts • Used a mixture of meso and racemic ansa-titanocenes • Stereo-rigid • Ethylene-bridged • Rac: chiral with C2-symmetric axis • Meso: achiral

  3. Unbridged metallocene catalysts • Rapid isomerization, low barriers • What kind of polymer is produced? • Atactic Polymer

  4. Unbridged metallocene catalysts • Added phenyl group to indene • Inhibits rate of ligand rotation

  5. Unbridged metallocene catalysts • Added phenyl group to indene

  6. Physical Properties of Polypropylene

  7. Olefin Polymerizations with Early Metal Catalysts ~ 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…

  8. 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

  9. 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 TopazTM (Tg = 140 – 200 °C)

  10. 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

  11. Late Metal Catalysts • Not useful…β-elimination Propagation Dissociation Β-Elimination Displacement

  12. Chain Transfer Mechanisms

  13. Chain Transfer Mechanisms

  14. Blocking of Axial Coordination Sites

  15. 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

  16. Mechanistic Model

  17. Polyethylene

  18. Poly (α–Olefins)

  19. Commercial Copolymers of Ethylene and Polar Vinyl Monomers ● Radical Initiation ● High temperatures, very high ethylene pressure

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