Catalytic synthesis and characterization of stereoregular and optically active polycarbosilanes

Stereoregular and optically active polycarbosilanes were synthesized by polyaddition of optically active allylsilane and propargylsilane, and ring-opening polymerization of optically pure benzosilacyclobutene. Polyaddition of allylsilane gave an isotactic polymer, but chirality at the silicon center was lost in the polymer and the polymer became optically inactive. Propargylsilane, having a triple bond, can maintain double-bond and single-bond carbons attached to silicon atom even after polyaddition by hydrosilylation, and the formed polymer showed optical activity. Catalytic ring-opening polymerization of an optically pure benzosilacyclobutene gave an optically active polymer with high stereoregularity with well-controlled molecular weight by using triethylsilane as a chain-transfer agent.