This paper describes the synthesis of interpenetrating polymer networks (IPN) materials based on polyethylene (PE) and polymethacrylates and the effect of ionising irradiation on degradation and grafting reactions in these materials. Two IPN systems, polyethylene/poly(butyl methacrylate-co-methyl methacrylate) and polyethylene/poly(dodecyl methacrylate-co-ethyl methacrylate), were synthesized by the in situ method using a peroxidic initiator and a divinyl crosslinker. During the synthesis the PE crosslinks and grafting reactions between PE and polymethacrylates occur. By electron beam irradiation the methacrylate phase partially degrades. After extraction with xylene a porous structure in the material is observed. The effect of the TPN composition, the synthesis conditions, and the electron beam irradiation on the amount of extractable material and the morphology of the IPN has been studied.