Silver nanoparticles were prepared by UV irradiation from silver salts, such as AgBF4 or AgNO3, when dissolved in an amphiphilic film of poly((oxyethylene)(9) methacrylate)-graft-poly((dimethyl siloxane)(n) methacrylate), POEM-gmPDMS. The in situ formation of silver nanoparticles in the graft copolymer film was confirmed by transmission electron microscopy (TEM), UV-visible spectroscopy, and wide angle X-ray scattering (WAXS). The results demonstrated that the use of AgBF4 yielded silver nanoparticles with a smaller size (similar to 5 nm) and narrower particle distribution when compared with AgNO3. The formation of silver nanoparticles was explained in terms of the interaction strength of the silver ions with the ether oxygens of POEM, as revealed by differential scanning calorimetry (DSC) and Xray photoelectron spectroscopy (XPS). It was thus concluded that a stronger interaction of silver ions with the ether oxygens results in a more stable formation of silver nanoparticles, which produces uniform and small-sized nanoparticles. DSC and small angle X-ray scattering (SAXS) data also showed the selective incorporation and in situ reduction of the silver ions within the hydrophilic POEM domains. Excellent mechanical properties of the nanocomposite films (3-5 X 10(5) dyn/CM2) were observed, mostly because of the confinement of silver nanoparticles in the POEM chains as well as interfaces created by the microphase separation of the graft copolymer film. (C) 2007 Wiley Periodicals, Inc.