Stereospecific Polymerization of Methyl Methacrylate with Single-Component Zirconocene Complexes: Control of Stereospecificity via Catalyst Symmetry

We report the stereospecific polymerization of methyl methacrylate (MMA) with single-component cationic zirconocene catalysts. The complexes Me 2 CCpIndZrMe(thf) + BPh 4 - ( 1 ) and Me 2 CCp 2 ZrMe(thf) + BPh 4 - ( 2 ) are active catalysts for the polymerization of MMA, in remarkable contrast to other cationic zirconocenes. While 1 yields highly isotactic poly(methyl methacrylate) (PMMA), 2 is syndiospecific at low temperatures. This is the first example for a rational control of PMMA microstructure via catalyst symmetry. Polymerization kinetics and stereospecificity control in MMA polymerization with 1 and 2 are discussed. On the basis of the experimental data, a possible polymerization mechanism is proposed.