Organotitanium-Mediated Stereoselective Coordinative/Insertive Homopolymerizations and Copolymerizations of Styrene and Methyl Methacrylate

Tryg R. Jensen, Sung Cheol Yoon, Aswini K. Dash, Lubin Luo, Tobin J. Marks

Research output: Contribution to journalArticle

65 Citations (Scopus)

Abstract

This contribution describes coordinative/insertive stereoregular homopolymerizations and copolymerizations of styrene and methyl methacrylate (MMA) mediated by a highly active single-site organotitanium catalyst. The catalyst system used to effect these polymerizations of nonpolar and polar olefinic monomers is prepared by in situ Zn reduction of the precursor derived from the reaction (Me5Cp)-TiMe3 + Ph3C +B(C6F5)4-. The resulting catalyst produces polystyrene (>95% syndiotactic, 170 000 g/mol molecular weight; s-PS) by the established coordinative/insertive pathway. The same catalyst mediates polymerization of MMA to poly(methyl methacrylate) (>65% syndiotactic, >70 000 g/mol molecular weight; s-PMMA) by a group transfer protocol-like (GTP-like) pathway (1,4 insertion mechanism). Under optimal conditions, this catalyst also mediates the copolymerization of MMA + styrene (1:19 ratio) at 50 °C to yield random ∼80% coisotactic poly[styrene-co-(methyl methacrylate)] (coiso-PSMMA) which contains ∼4% MMA. Control experiments argue that a single-site Ti catalyst is the active species for the copolymerization. The catalyst formation process is quite general, and a variety of reducing agents can be substituted for Zn and still effect copolymerization. Control experiments also indicate that known noncoordination copolymerization mechanisms (i.e., ionic or radical) cannot explain this copolymerization. We suggest a new mechanism involving sequential conjugate addition steps to explain these copolymerization results.

Original languageEnglish
Pages (from-to)14482-14494
Number of pages13
JournalJournal of the American Chemical Society
Volume125
Issue number47
DOIs
Publication statusPublished - Nov 26 2003

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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