Copolymers (I-IV) of 2-acryloylamino-9,16,23-tri(t-butyl)phthalocyanine (APc(t-Bu)(3)) and acrylamide derivatives were prepared and their catalytic activity for oxidation of 2-mercaptoethanol was examined. Copolymers (II and IV) of APc(t-Bu)(3) and N-isopropylacrylamide revealed a lower critical solution temperature phenomenon at 29 degrees C in carbonate buffer, that is to say, the copolymers dissolving in buffer solution below 29 degrees C separated out as precipitate above 29 degrees C. The catalytic activity of polymer IV, which was prepared by metalation of copolymer II, markedly changed around 29 degrees C. Copolymer IV served as a homogeneous catalyst of autoxidation of 2-mercaptoethanol below 29 degrees C. In contrast, the catalytic activity drastically decreased above 29 degrees C because of separation as precipitate.