Significant proximity and cocatalyst effects in binuclear catalysis for olefin polymerization

Hongbo Li, Charlotte L. Stern, Tobin J. Marks

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Abstract

We describe here the implementation of methylene-bridged binuclear "constrained geometry catalyst" (μ-CH 2-3,3′) {(η 5-indenyl)[1-Me 2Si( tBuN)](ZrMe 2)} 2 (Cl-Zr 2) to produce high-M w branched polyethylene. In ethylene homopolymerization, ∼70x increases in molecular weight are achieved with (C1-Zr 2) vs (μ-CH 2CH 2-3,3′){(η 5-indenyl)[1-Me 2Si( tBuN)](ZrMe 2)} 2 (C2-Zr 2) under identical polymerization conditions using (Ph 3C +) 2[1,4-(C 6F 5) 3BC 6F 4B(C 6F 5) 3] 2- (B 2) as the cocatalyst for both. With MAO as the cocatalyst, ∼600x increases in polyethylene molecular weight are achieved with (μ-CH 2CH 2-3,3′){(η 5- indenyl)[1-Me 2Si( tBuN)](ZrCl 2)} 2 (C2-Zr 2Cl 4) and (μ-CH 2-3,3′) {(η 5-indenyl)[1-Me 2Si( tBuN)](ZrCl 2)} 2 (C1-Zr 2Cl 4) vs mononuclear [1-Me 2Si(3-ethylindenyl)( tBuN)]ZrCl 2 (Zr 1Cl 2). In the ethylene + 1-hexene copolymerization, C1-Zr 2 enchains 3x more 1-hexene than does C2-Zr 2 under identical polymerization conditions (B 2 as cocatalyst). With MAO as the cocatalyst, C2-Zr 2Cl 4 enchains 3.5x more, and C1-Zr 2Cl 4 4.2x more, 1-hexene than does Zr 1Cl 2. When the polar solvent C 6H 5Cl is used as the polymerization medium, dramatic compression in the dispersion of polymerization activities and molecular weights is found. Both homopolymerization and copolymerization results argue that achievable Zr-Zr spatial proximity significantly influences chain transfer rates and selectivity for comonomer enchainment and that such proximity effects are highly cocatalyst and solvent sensitive.

Original languageEnglish
Pages (from-to)9015-9027
Number of pages13
JournalMacromolecules
Volume38
Issue number22
DOIs
Publication statusPublished - Nov 1 2005

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ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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