Although polymethacrylates generally degrade under ionising irradiation, differences in degradation behaviour exist amongst various polymethacrylates. The radiation behaviour of different methacrylate polymers was investigated on interpenetrating polymer networks (IPN) based on polyethylene and methacrylate copolymers, synthesised via an in situ method. Changes in chemical structure such as hydroxyl groups, unsaturated C=C bonds, crosslinking, main chain scission and in composition caused by irradiation have been characterised by FTIR. Linking between the two IPN components caused by irradiation has been observed by TGA and pyrolysis-GC-MS. Mechanical properties in dependence on radiation doses have been characterised by tensile test and dynamic-mechanical analysis.