Stereospecific Polymerization of Methacrylates with Dimethylsilylene-bridged Zirconocene Catalysts

Polymerization of methyl methacrylate (MMA) was conducted with a series of dimethylsilylene-bridged zirconocene complexes (rac-Me2ilnd2ZrMe2, 1; Me2SiCpIndZrMe2, 2; Me2SiCpFluZrMe2, 3: Cp, cyclopentadienyl; Ind, indenyl; Flu, fluorenyl) to investigate the effects of the cyclopentadienyl ligand. Thezirconocene complexes were activated by [Ph3C][B(C6F5)4] or [PhMe2NH][B(C6F5)4]in the presence of diethylzinc. It was found that 1 and 2 gave polymers but 3 did not at 0°C. The dependence of polymer yieldand molecular weight on polymerization time indicated that some chain transfer reaction occurred in both systems. 13C NMR analysis revealed that C1symmetric 2 as well as C 2-symmetric 1 gave isotactic rich polymer (mmmm = 84–87%) by enantiomorphic-site controlled mechanism. Polymerization of allyl methacrylate (ALMA) was also conducted with Cp2ZrMe2 and 1. These catalysts selectively polymerized the methacryl group to give syndiotactic-rich and isotactic polymers, respectively with pendant allyl group.