Synthesis and Polymerization of Silylethylene Containing a Stereogenic Silicon Center

Hydrosilylation of acetylene with a chiral silane, R-(+)-methyl-1-naphthylphenylsilane [R-(+)-MeNpPhSi*H], in the presence of H2PtCl6·xH2O proceeds with retention of the configuration of the stereogenic silicon center and produces a chiral vinylsilane or silylethylene [S-(+)-MeNpPhSi*Vi] of high optical purity under mild conditions (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 [a] D up to −28.1°, while polymerizations of the racemic monomer by a chiral initiator n-BuLi/(−)-sparteine produce polymers with [a] D up to +275°. Thus the sign of optical rotation of the polymers can be controlled by different combinations of monomer and catalyst. The magnitude of the optical rotation can be ‘‘tuned’’ by changing the polymerization temperature, with high temperature generally favoring random propagation. All the polymers have low polydispersity indexes (Mw/Mn down to 1.02) or possess narrow molecular weight distributions. Spectroscopic characterization confirms the molecular structure of the 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) and possess a high glass transition temperature (Tg q 380°C). 7 1998 Elsevier Science Ltd. All rights reserved