Network polymers. II. Experimental study of swelling

Abstract

AbstractThe swelling behavior of vinyl‐divinyl network polymers has been studied. Various monovinyl monomers (styrene, vinyltoluene, p‐tert‐butylstyrene, a series of n‐alkyl methacrylates), divinyl monomers (divinylbenzene, ethylene dimethacrylate), and contacting solvents (ranging from n‐alkanes to water) have been used. Attention is directed to the effects of introducing an initial good‐solvent diluent at the time of polymerization. Results are interpreted in terms of changes of the free energies of solvent‐Polymer mixing and network deformation. The relaxed volume of the network is shown to be closely related to the volume at which it is formed. The network modulus increases with increasing divinyl content and decreases sharply with increasing initial dilution. With high crosslinking and moderate initial dilution, an interesting special case arises: the volume of formation of the network, its relaxed volume, and its equilibrium swollen volume are all almost identical, and the swollen volume is essentially independent of polymer–solvent interaction. Networks prepared from monomers with large pendant groups exhibit a built‐in dilution effect.