Synthesis and polycondensation of a cyclic oligo(phenylsilsesquioxane) as a model reaction for the formation of poly(silsesquioxane) ladder polymer

A tetracyclo(phenylsilsesquioxane) (T4) was first synthesized by the oligomerization of the low molecular weight hydrolysate of trichlorophenylsilane (TCP) by catalysis of the weak base, NaHCO3, followed by KOH-catalyzed polycondensation in toluene to form poly(phenylsilsesquioxane) (PPQS). The rate of polycondensation of T4 was much slower than that of direct polycondensation of the TCP hydrolysate under identical conditions. The molecular weight of the former product (M-n = 35800) was significantly lower than that of the latter product (M-n = 110000). X-Ray scatterings of the PPQS prepared by both processes were slightly different, probably due to the difference in structural regularity or branched structure. These data suggest that the polycondensations of T4 and the TCP hydrolysate should be driven through different reaction mechanisms, although the formation of the double strand ladder chain in the produced PPQS should be common to both.