Stereoselective feature in anionic ring-opening polymerization of 2-(1-naphthyl)-2-phenyl-5,5-dimethyl-1-oxa-2,5-disilacyclopentane and influence of tacticity on the thermal property of polymers

The stereoselective feature in the anionic ring-opening polymerization of racemic 2-(1-naphthyl)-2-phenyl-5,5-dimethyl-1-oxa-2,5-disilacyclopentane was investigated by C-13 NMR analysis of the dyad sequence of the resulting polymer. The influences of initiators, polymerization temperature, and solvents on the tacticity of the polymer were discussed. It was found that the polymerization using PhLi as an initiator could afford a polymer rich in syndiotacticity (r/m = 65/35 at -20 degrees C). The stereoregulation was tentatively considered due to the different stability or reactivity of the diastereomeric intermediates comprised of the propagating chain end, monomer, and countercation. The isotactic polymer prepared from the optically active monomer showed a similar T-g to that of the syndiotactically rich polymer prepared from the racemic monomer, but the former exhibited significantly better thermal stability than the latter.