Effect of temperature on the terminal relaxation of branched polydimethysiloxane

Abstract The effect of long chain branching on the rheology of polydimethylsiloxane (PDMS) was investigated. Due to the low glass temperature and high thermal stability of PDMS, the terminal relaxation could be measured at temperatures more than 270° above the polymer's glass temperature. Over the measured range, the data for all samples conformed to the time–temperature superposition principle and exhibited Arrhenius behavior. Activation energies, determined from the zero-shear viscosity of a linear and a commercial PDMS were equal to within the experimental error. Branching of the latter by chemical reaction did not change the temperature dependence of its terminal shift factors. This demonstrates that similar to polyisobutylene, but quite distinct from polyethylene, 1,4-polyisoprene, and 1,4-polybutadiene, long-chain branching does not affect the temperature dependence of the terminal rheology of PDMS.