The mechanism of B(C6F5)3 catalyzed Si—H/Si—OR polycondensation reaction was studied through the quantum chemistry methods.Poly(silphenylene-siloxane)s were prepared by polycondensation of 1

4-bis(dimethylsilyl)benzene (BDSB) and dimethyldimethoxylsilane

vinylmethyldimethoxylsilane and diphenyldimethoxylsilane respectively.The microstructure of the polymer was characterized by 29Si NMR and the influence of vinyl and phenyl groups of alkoxylsilane on the microstructure of the polymer was also discussed.B(C6F5)3 first activated Si—H to form weak adduct

then Si—OR attacked Si—H/B(C6F5)3 adduct to break Si—H and form oxonium ion complex.The decomposition of the complex occurred by the H- transfer to one of the three electrophilic centers

which explained the competition between condensation and Si—H/Si—OR exchange.Vinyl or phenyl group of alkoxysilane decreased the positive charge of Si atom and increased the positive charge of C which bonded to O

and it also reduced the strength of C—O

resulting in more alternated polymers.