1 / 26

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

bart
Download Presentation

Soluble Metallocene Cataysts Polyethylene

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related