Sonochemical synthesis of well-defined polysilanes

Monomodal polysilanes with relatively narrow molecular weight distributions (M;Since high polymer is formed at low monomer conversion and the molecular weight is independent of the mole ratio of (Mt) ;The strong solvent effect, the influence of crown-ether and cryptand on polymerization rate, the formation of soluble polymers from reductive coupling of trichlorosilanes with sodium, and copolymerization studies support anionic intermediates. Anionic species can be formed via radical intermediate. Radical intermediates are formed from the first electron-transfer from alkali metals to chloro-terminated polymeric chains. The presence of radical species has been proved by the trapping experiments with dichlorosilanes containing pendant alkenyl dichlorosilanes. These results suggest that radical species should be present as short-living species which are converted into anionic species by the second electron-transfer reaction with alkali metals. Anionic species react with monomers faster than with chloro-terminated polymer chains.;It has been established that polymerization is strongly dependent on substituents at silicon atoms, on solvents, on alkali metals, and on reaction temperature. Dichlorosilanes containing one aromatic group are more reactive than dialkyldichlorosilane because the aromatic group facilitates an electron transfer. Polymerization of methylphenyldichlorosilane with potassium in toluene does not lead to a polysilane, due to "too high" reactivity of potassium and side reactions. Less reactive sodium provides, however, high molecular weight polysilane.