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

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...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2003-11, Vol.125 (47), p.14482-14494
Main Authors: Jensen, Tryg R, Yoon, Sung Cheol, Dash, Aswini K, Luo, Lubin, Marks, Tobin J
Format: Article
Language:English
Subjects:
Applied sciences
Copolymerization
Exact sciences and technology
Organic polymers
Physicochemistry of polymers
Preparation, kinetics, thermodynamics, mechanism and catalysts
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Summary: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.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja0363664