Elasticity of hydrogels prepared by photopolymerization of poly(ethylene oxide) macromonomers

For polymer gels prepared by the photoinitiated radical polymerization of poly(ethylene oxide) macromonomers with methacrylate end groups, elastic moduli were studied as a function of their degree of swelling. It was shown that the pattern of this dependence changes when the initiator concentration is varied over a wide range. Upon swelling, the gels prepared at high initiator concentrations become softer, as predicted by the rubber elasticity theory, whereas the gels synthesized at low initiator concentrations become more rigid. At a fixed degree of swelling, the elastic moduli of the former gels are lower than those of the latter gels. The effects observed are explained by the influence of the initiator concentration on the length of the polymethacrylate chains formed in the course of polymerization that act as multifunctional network junctions.