Interpenetrating polymer networks (IPNs) based on polyethylene (PE) and poly(methacrylate)s were prepared by in situ polymerization. A co-continuous phase morphology was obtained. The use of dodecyl methacrylate produces good compatibility between PE and poly(methacrylate)s. The degree of PE crosslinking in IPNs has been estimated by comparison of the melting temperatures of PE crystallites in pure crosslinked PE with those in IPNs.