Crossover of the concentration dependence of swelling and elastic properties for polysiloxane networks crosslinked in solution

Abstract

We have investigated the preparation concentration dependence of the polymer volume fraction and the elastic modulus of the equilibrium swollen polydimethylsiloxane networks in toluene. The networks were prepared by the end-linking method in solution with a wide range of concentration. The network samples were attempted to be as small amount of structural defects as possible. The crossover has been observed for the preparation concentration dependence of the degree of equilibrium swelling and the elastic modulus. The crossover concentrations agree with each other, and are almost identical with the boundary concentration between the semidilute and the concentrated regime for the end-to-end distance of the polymer chain. The theoretical predictions which describe the experimental results have been derived as a function of the polymer volume fraction of preparation and swollen state, considering the effect of trapped entanglements on the elasticity and the concentration regime of preparation and swollen state. The good agreements of the theoretical predictions with the experimental results suggest that the trapped entanglements contribute to the elastic modulus together with the chemical crosslinks, and the crosslinking points moves affinely relative to the global polymer network on swelling.