The polysilsesquioxane having mercapto, dimethylamino, and phenyl groups (PAMPSQ) was prepared from the corresponding trimetboxysilanes by co-condensation under basic conditions. The mercapto group on PAMPSQ was utilized as an initiator for graft copolymerization of N-isopropylacrylamide and N,N-dimethylacrylamide. The grafting of the copolymer proceeded effectively to give the thermoresponsive polysilsesquioxane derivative (GrPSQ) without the formation of gel product. The obtained GrPSQ was amphiphilic and provided the property of thermoresponsive reversible aggregation. The aggregation temperatures of GrPSQ varied in buffer solutions showing different pH values. Furthermore, the formation of ammonium salts utilizing dimethylaminio groups with carboxylic acids or halogen compounds led to a rise in aggregation temperature. (c) 2006 Published by Elsevier Ltd.