Mechanism of Anionic Ring-Opening Polymerization of Silacyclopent-3-enes

摘要

Anionic ring-opening polymerization of silacyclopent-3-enes has characteristicswhich are different from those of anionic living polymerizations of 1,3-dienes. High molecular weights are obtained in most cases but generally with most probable molecular weight distributions. The polymerization is stereospecific. Poly(1-sila-cis-pent-3-enes) are obtained. Ring opening polymerization of 1,1,3-trimethy1-1-silacyclopent-3-ene is found to be regioselective at -78 C to yield a polymer in which cis-1,4-isoprene units are joined to diethylsilylene units almost exclusively in a head to tail orientation. Finally, anionic polymerization of 1-methy1-1-silacyclopent-3-ene is found to yield poly(1-methy1-1-silacyclopent-3-ene is found to yield poly(1-methy1-1-sila-cis-pent-3-ene) of low molecular weight. This permits end group analysis by 1H, 13C and 29Si NMR spectroscopy. Signals are observed which are consistent with the presence of 1-methy1-1-silacyclopent-3-ene rings. These are probably end groups. A mechanism consistent with the above is discussed.