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Soluble Metallocene Cataysts Polyethylene

Soluble Metallocene Cataysts Polyethylene. Bis(cyclopentadienyl)zirconium dichloride Plus methylaluminoxane (MAO) 5,000 kg PE / g Zr / hr (indefinitely active). Soluble Metallocene Cataysts Polypropylene. Soluble Metallocene Cataysts. Used a mixture of meso and racemic ansa -titanocenes

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Soluble Metallocene Cataysts Polyethylene

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  1. Soluble Metallocene CataystsPolyethylene • Bis(cyclopentadienyl)zirconium dichloride • Plus methylaluminoxane (MAO) • 5,000 kg PE / g Zr / hr (indefinitely active)

  2. Soluble Metallocene CataystsPolypropylene

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

  4. Rac Ansa Catalysts Non-superimposable Mirror Images

  5. Soluble Metallocene Cataysts Ewen J. Am. Chem. Soc.1984

  6. PP from ansa-Metallocene Catalysts • Methyl pentad region • Fractions of iso-PP versus atactic-PP tracks with ratio of racemic to meso catalyst levels • MWs on each sample were similar indicating that both stereo-isomers of the catalyst give rise to similar propagation and termination rate constants

  7. Soluble Metallocene Cataysts • Confirmed Ewen’s proposal that it was the chiral ansa-metallocene that was responsible for the formation of isotactic PP • Made the zirconium derivative • 7,700 kg PP / mol Zr / hr (!) 1985 Kaminsky and Britzinger

  8. Mechanism for Isotactic PP • Conformational modeling studies (Corradini 1991) • The growing polymer chain is forced into the open region • Chirality of the metallocene is relayed to the incoming monomer through the orientation of the methyl group • Since C2-symmetry, both reactions sites are homotopic • Therefore selective for the same olefin enantioface • Giving rise to isotactic PP

  9. Soluble Metallocene CataystsPolypropylene

  10. Rac Ansa Catalysts C2 Axis of Symmetry Binding Sites are Homotopic

  11. H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H

  12. Cs symmetry • Cp of different size • Steric bulk flanking the metallocene wedge with an open region in center

  13. How to make this? • Hemi-isotactic • Hemi-syndiotactic

  14. … … m m r r m m m m r r r r m m m m r

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

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

  17. Physical Properties of Polypropylene

  18. 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…

  19. 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

  20. 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)

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

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