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Title: Synthesis of optically active poly(silyethylene)s containing a stereogenic silicon center
Authors: Wan, Xinhua
Kwok, Hoi-Sing
Tang, Ben-Zhong
Keywords: Optically active polymers
Chemical synthesis
Chiral silicon
Liquid crystal displays
Issue Date: Feb-1997
Citation: Proceedings of the Fourth Asian Symposium on Information Display (Feb 13-14, 1997), Hong Kong, HKUST, 1997. p. 187-190
Abstract: Hydrosilylation of acetylene with a chiral silane, R-(+)-methyl-1-naphthyl-phenylsilane [R-(+)-Me-NpPhSi*H], in the presence of H2PtCI6·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 (50oC) in high chemical yield (85%). Anionic polymerizations of the chiral silylethylene monomer by an achiral initiator n-BuLi yield optically active polymers with [α]D20 up to -28.1o, while polymerizations of the racemic monomer by a chiral initiator n-BuLi/(-)-sparteine produce polymers with [α]D20 up to +275o. 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 polydispersity indexes (Mw/Mn 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-naphthyl-phenylsilyl side chain. The polymers are thermally stable (onset temperature for weight loss in air: 380oC), possess high glass transition temperature (Tsub>g >380sup>oC), and may find a wide range of applications in the optical display systems.
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