New thermosensitive copolymers were obtained by copolymerization of styrene with N-methylacrylamide, N-ethylacrylamide or N,N-dimethylacrylamide. The turbidity measurements showed that these polymers can undergo a thermally induced phase transition at various temperatures, depending on their chemical composition, molecular weight and concentration in water. Fluorescence measurements indicated the occurrence of aggregation through hydrophobic interactions even below the lower critical solution temperature. The enthalpy and cooperativity of phase transition determined by microcalorimetry were strongly dependent on the chemical structure of the N-alkylacrylamide comonomer. (C) 2003 Elsevier Science Ltd. All rights reserved.