CdS nanoparticles were prepared using amphiphilic urethane acrylate nonionomer (UAN) precursor chains having a poly(propylene oxide)-based hydrophobic segment and a hydrophilic poly(ethylene oxide) segment. Cadmium salts were first dissolved in UAN/styrene solutions, and then the solutions were copolymerized to obtain poly(urethane acrylate-co-styrene) films containing dissolved cadmium salts. After reduction with H2S gas, freestanding films containing CdS nanoparticles were obtained. Transmission electron microscopy images of the films showed that 9.67-nm CdS nanoparticles were dispersed within the poly(urethane acrylate-co-styrene) matrix. The formation of CdS nanoparticles was also confirmed with UV absorption spectra and photoluminescence emission spectra of the films. Transmission electron microscopy and dynamic mechanical analysis measurements confirmed that hydrophilic /hydrophobic microphase separation in UAN/styrene solutions occurred during the dissociation of the cadmium salts, and the microphase-separated structures were locked in by crosslinking copolymerization. (c) 2005 Wiley Periodicals, Inc.