Synthesis of optically active poly(silyethylene)s containing a stereogenic silicon center

Hydrosilylation of acetylene with a chiral silane, R-(+)-methyl-1-naphthyl-phenylsilane [R-(+)-MeNpPhSi*H], in the presence of H₂PtCl₆·xH₂O proceeds with retention of configuration of the stereogenic silicon center and produces a chiral vinylsilane or silylethylene [S-(+)-MeNpPhSi*Vi] of high optical purity under mild condition (50 °C) in high chemical yield (85%). Anionic polymerizations of the chiral silylethylene monomer by an achiral initiator n-BuLi yield optically active polymers with [α]_D ²⁰ up to -28.1°, while polymerizations of the racemic monomer by a chiral initiator n-BuLi/(-)-sparteine produce polymers with [α]_D ²⁰ up to +275°. Thus the sign of optical rotation of the polymers can be controlled by different combination of monomer and catalyst. Magnitude of the optical rotation can be `tuned' by changing polymerization temperature with high temperature generally favoring random propagation. All the polymers have low polydispersity indexes (M_w/M_n down to 1.02) or possess narrow molecular weight distributions. Spectroscopic characterization confirms the molecular structure of polymers to be poly(silylethylene), that is, a polyethylene main chain with a bulky methyl-1-naphthylphenylsilyl side chain. The polymers are thermally stable (onset temperature for weight loss in air: 380 °C), possess high glass transition temperature (T_g>380 °C), and may find a wide range of applications in the optical display systems.