An investigation of the theory of rubber elasticity using irradiated polydimethylsiloxanes

Abstract High‐energy electrons were used to crosslink a series of polydimethylsiloxanes. Equilibrium tension measurements at low elongations were used to determine the number of chains between crosslinks as given by the kinetic theory of elasticity. After a rapid increase at low radiation doses the number of chains was found to be proportional to the dose. The linear relationship between number of chains and dose, found at higher doses, extrapolated to zero dose, has a positive intercept. This intercept was independent of the initial molecular weight of the polymer and was taken to be a measure of the effect of the maximum number of permanent entanglements in this polymer. The dependence of the number‐average molecular weight of irradiated polydimethylsiloxane fluids on radiation dose was determined. The data were analyzed to find the efficiency of crosslink formation in this polymer. The number of chains between crosslinks produced by a given dose and determined by the kinetic theory was found to be only one‐half the number to be expected from the measurement of the molecular weights of the irradiated fluids.