H-1 NMR spectroscopy was used to investigate temperature-induced phase transitions in D2O solutions of poly(N-isopropylmethacrylamide) (PIPMAm)/poly(N-isopropylacrylamide) (PIPAAm) mixtures and P(IPMAnVIPAAm) random copolymers of various composition on molecular level. While two phase transitions were detected for PIPMAm/PIPAAm mixtures, only single phase transition was found for P(IPMAnVIPAAm) copolymers. The phase transition temperatures of PIPAAm component (appears at lower temperatures) are not affected by the presence of PIPMAm in the mixtures; on the other hand, the temperatures of the phase transition of PIPMAm component (appears at higher temperatures) are affected by the phase separation of the PIPAAm component and depend on concentration of the solution. For P(IPMAm/IPAAm) random copolymers, a departure from the linear dependence of the transition temperatures on the copolymer composition was found for a sample with 75 mol% of IPMArn monomeric units. (C) 2004 Elsevier Ltd. All rights reserved.