Properties of Poly(Dimethylsiloxane) Networks Prepared in Solution, and their Use in Evaluating the Theories of Rubberlike Elasticity

Abstract

Abstract Poly(dimethylsiloxane) networks were prepared by γ irradiation of solutions of the polymer in cyclohexane; concentrations employed corresponded to volume fractions ν2,s of polymer ranging from 0.3 to 1.0. The moduli of these networks were obtained by stress—elongation measurements on the extracted, dried networks, and the relative degrees of crosslinking were obtained by swelling equilibrium experiments. These data were used to calculate the dependence of the modulus on the volume at which the crosslinking had been carried out. Comparison of experimental and theoretical values of this quantity lends strong support to the theory of rubberlike elasticity developed by Flory and coworkers. In addition, for samples having equal moduli, deviations from the form of the theoretical stress—elongation relationship decrease with decreasing ν2,s, with the strongest such dependence apparently occurring at small values of this volume fraction. In contrast, non-equilibrium effects exhibited by these networks also decrease with decreasing ν2,s, but the largest change is observed at large values of ν2,s. At constant ν2,s, increase in degree of crosslinking seems to increase the cited deviations from theory but to decrease nonequilibrium behavior. These additional results suggest that such deviations from theory can be, at most, only partially due to nonequilibrium effects.