The polysilsesquioxane having mercapto and phenyl groups (PMPSQ) was prepared from the corresponding trimetboxysilanes by co-condensation under basic conditions. The mercapto groups on PMPSQ were utilized as the initiators for the graft polymerization of N-isopropylacrylamide (NIPAM) with the comonomer such as N,N-dimethylacrylamide (DMAA) or hydroxyethyl acrylate under UV irradiation. The grafting of the copolymers proceeded effectively to give the functionalized polysilsesquioxane derivatives, in which the monomer unit ratios almost reflected the feed molar ratios of the monomers and no formation of gel product was observed. These grafted polysilsesquioxanes could be dissolved in water and showed the property of thermoresponsive gel formation. (c) 2006 Elsevier Ltd. All rights reserved.