Hyperbranched polyalkenylsilanes by hydrosilylation with platinum catalysts. I. Polymerization

Hyperbranched polycarbosilanes were synthesized by hydrosilylation addition of methyldivinylsilane, methyldiallylsilane, triallylsilane, and methyldiu ndecenylsilane. Molecular mass distributions of the hyperbranched polymers were investigated upon systematic variation of the reaction conditions. The formation of hyperbranched polycarbosilanes depended strongly on the react ion conditions and the monomer structure. Although cyclization reactions im peded the build up of molecular weight, crosslinking due to rearrangement r eactions caused the formation of multimodal molecular weight distributions and gelation. Crosslinking could be avoided by the appropriate choice of th e reaction conditions. In the case of methyldiundecenylsilane, where the di stance between the double bond and silicon atom essentially was enlarged, h igh molecular weight polymers with remarkably narrow molecular weight distr ibutions were obtained; the molecular mass could be controlled by subsequen t addition of further monomer. (C) 2000 John Wiley & Sons, Inc.