Structure and Viscosity of Poly(dimethylsiloxanes) with Random Branches

Viscosity rise and extent of reaction were followed during the stepwise polymerization of vinyl-terminated poly(dimethylsiloxane) with tri- and tetrafunctional hydrosilanes. Gel point results and M_w data by light scattering agree with predictions from branching theory. This indicates that the influence of side reactions, substitution effects, and ring formation is small. The bulk viscosity of the branched molecules was found to correlate with the weight average molecular weight of the longest linear chain through the molecules, M_{L, w} and with gM_w where g is the ratio of branched to linear polymer radii of gyration.