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Analysis of i -PP made by Ziegler Natta Catalyst

Analysis of i -PP made by Ziegler Natta Catalyst. 13 C NMR analysis shows:. …. …. m m m m m m m r r m m m m m m m m. Enantiomorphic Site Control. …. …. m m m m m m m r m m m m m m m m m. Chain - end Control.

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Analysis of i -PP made by Ziegler Natta Catalyst

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  1. Analysis of i-PP made by Ziegler Natta Catalyst • 13C NMR analysis shows: … … m m m m m m m r r m m m m m m m m Enantiomorphic Site Control … … m m m m m m m r m m m m m m m m m Chain - end Control

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

  3. Soluble Metallocene CataystsPolypropylene

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

  5. Rac Ansa Catalysts Non-superimposable Mirror Images

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

  7. 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

  8. 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

  9. 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

  10. Soluble Metallocene CataystsPolypropylene

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

  12. 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

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

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

  15. … … m m r r m m m m r r r r m m m m r

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