Polymeric organosilicon systems .25. Preparation of branched polymers by regiospecific hydrosilylation of poly[(silylene)diethynylenes] and their properties

Regiospecific 1,2-hydrosilylation reactions of (dimethylsilylene)-, (methylphenylsilylene)-, and (diethylsilylene)diethynylene polymers with 1,4-bis(methylphenylsilyl)benzene in the presence of a catalytic amount of Rh-6(CO)(16) afforded the respective branched polymers with high molecular weights in high yields. The rate of the hydrosilylation and degree of branching were found to be affected by polarity of the solvent, amounts of the catalyst, reaction temperature, and concentration of the polymers. It was found that degradation of the resulting branched polymers and also starting polymers readily took place when they were treated with ethanol in the presence of triphenylphosphine. The reaction of poly-[(tetramethyldisilanylene)diethynylene] with hydrosilanes in the presence of the rhodium-(0) catalyst proceeded to give hydrosilylation products, but scission of the polymer chain was also observed. A mechanism for the degradation of polymers is discussed on the basis of the results obtained for model compounds.