The emulsion copolymerization of a partially water-soluble monomer, methyl methacrylate (MMA), and a water-soluble polymerizable cosurfactant, hydroxyethyl methacrylate (HEMA), was investigated. The microstructure of the copolymer varied as the HEMA concentration increased. The copolymer microstructure influenced drug entrapment and was studied with respect to the variation in the MMA/HEMA ratio, the crosslinker concentration, and the method of nanoparticle separation from the dispersion. The subsequent release of a lipophilic drug, carbamazepine, from nanoparticles was studied at three different copolymer compositions. (C) 2004 Wiley Periodicals, Inc. J. Appl Polym Sci 92: 402-409, 2004.