Polyethylene/polymethacrylate interpenetrating polymer networks (PE/PMA IPN) form a matrix-particle or a co-continuous morphology that can be adjusted by the composition and synthesis conditions. Based on the fact that PMA degrades whereas PE crosslinks when they are exposed to energetic irradiation, we developed a new approach to create a porous structure by electron beam irradiation. IPN systems that differ in the methacrylate components and composition were studied. One system contains poly(butyl methacrylate-co-methyl methacrylate) (BMA-co-MMA) and the other contains poly(dodecyl methacrylate-co-ethyl methacrylate) (DMA-co-EMA) as the PMA phase. After electron beam irradiation followed by extraction with xylene, both IPN systems have a porous structure that is permeable to water. However, the structure and size of the pores depend on the PMA components and the synthesis conditions. PMAs with long aliphatic side chains degrade less than PMAs containing only short aliphatic pendant groups. Therefore, the PE/BMA-co-MMA IPN forms bigger pores than PE/DMA-co-EMA, resulting in a higher water flux. The molecular cutoffs of the IPN are characteristic for microfiltration or ultrafiltration. (C) 2003 Wiley Periodicals, Inc.