SYNTHESIS AND POLYMERIZATION OF SILYLETHYLENE CONTAINING A STEREOGENIC SILICON CENTER

Hydrosilylation of acetylene with a chiral silane, R-(+)-methyl-1-naph thylphenylsilane [R-(+)-MeNpPhSiH], in the presence of H2PtCl6. xH(2) O proceeds with retention of the configuration of the stereogenic sili con center and produces achiral vinylsilane or silylethylene [S-(+)-Me NpPhSiVi] of high optical purity under mild conditions(50 degrees C) in high chemical yield (85%). Anionic polymerizations of the chiral si lylethylane monomer by an achiral initiator n-BuLi yield optically act ive polymers with [alpha](D)(20) up to -28.1 degrees, while polymeriza tions of the racemic monomer by a chiral initiator n-BuLi/(-)-spartein e produce polymers with [a](D)(20) up to +275 degrees. Thus the sign o f optical rotation of the polymers can be controlled by different comb inations of monomer and catalyst. The magnitude of the optical rotatio n can be ''tuned'' by changing the polymerization temperature, with hi gh temperature generally favoring random propagation. All the polymers have low polydispersity indexes (Mw/Mn down to 1.02) or possess narro w molecular weight distributions. Spectroscopic characterization confi rms the molecular structure of the polymers to be poly(silylethylene), that is, a polyethylene main chain with a bulky methyl-1-naphthylphen ylsilyl side chain. The polymers are thermally stable (onset temperatu re for weight loss in air: 380 degrees C) and possess a high glass tra nsition temperature (T-g > 380 degrees C). (C) 1998 Elsevier Science L td. All rights reserved.