γ‐irradiation of siloxane polymers in air and vacuum at several temperatures

Abstract

AbstractThe effects of γ‐irradiation on two polysiloxanes in environments of air and vacuum at several selected temperatures were studied. The physical property monitored during the γ‐irradiation of the two polysiloxanes was the change in dynamic modulus which, in turn, is proportional to the change in the number of elastically effective chains in the polymer network. The measurements were accomplished by recording in situ the freeend response of the polymeric cantilever reeds in forced resonance at and near their fundamental frequency of resonance. The apparent energy of activation of crosslinking for the polydimethylsiloxane polymer was found to be 0.56 kcal./mole in vacuum over a limited temperature range, and 3.5 kcal./mole in air. For the polydimethyl‐diphenylsiloxane polymer, the apparent energy of activation was found to be about 1.3 kcal./mole in vacuum, whereas in air the polymer response was complex, displaying both scissioning and crosslinking reactions so that a value could not be obtained. The ability of the pendant phenyl groups to reduce the effective crosslinking rate was found to be sensitive to both temperature and environment.