A novel poly(ethylene oxide) macroinimer (PEO-macronimer) possesing methacryloyl and tertiary amino end groups was prepared by ring-opening polymerization of ethylene oxide initiated by potassium 2-methylaminoethoxide and termination of living ends of PEO with methacryloyl chloride. NMR analysis showed that the macronimer contains equal amount of amino and methacrolyl groups indicating efficient initiation and termination processes. The dimethylamine end group in conjunction with benzophenone under UV irradiation produced ternary amine methylene radicals via H-abstraction mechanism which initiates the polymerization. Photopolymerization in solutions at high macroinimer concentration or in films resulted in the formation of insoluble networks. The crosslinked polymers exhibit high swelling capacity in organic solvents and water due to the hyperbranched nature. (C) 2002 Elsevier Science Ltd. All rights reserved.