Viscosity measurements in branched silicones

Exposure to high energy radiation offers a means of producing controlled branching in long chain polymers. Branched silicone polymer molecules were obtained by exposing linear molecules to high energy radiation. The increase in weight‐average molecular weight calculated theoretically from the radiation dose was compared with the value deduced from measurements of intrinsic and bulk viscosity, ignoring the effect of branching. The ratio of these measurements show the apparent reduction in molecular weight (as measured by viscosity methods) when branched molecules are present. In particular it is found that the reciprocal bulk viscosity decreases uniformly with degree of branching (or crosslinking) until the gel point, when the weight‐average and bulk viscosity become infinite.