A diblock copolymer (P98N100) composed of a biocompatible water-soluble block (PMPC) and a lower critical solution temperature (LCST) type thermo-responsive block (PNIPAM) was prepared via controlled radical polymerization. To dissolve fullerene (C-60) in water, the C-60/P98N100 complex was prepared by mixing C-60 and P98N100 powders. The maximum solubilized C-60 concentration in water was 1.39 g/L, as estimated from UV-vis adsorption, when the polymer concentration was 5.0 g/L. The percent transmittance of the aqueous solution of the C-60/P98N100 complex decreased above 36 degrees C due to inter-complex association above the LCST for the PNIPAM block. While the hydrodynamic radius of C-60/P98N100 complex was 135 nm at 20 degrees C, it increased to 161 nm at 50 degrees C. Despite the observation of H-1 NMR signals from PMPC and PNIPAM blocks for the C-60/P98N100 complex in D2O at room temperature, the signals from PNIPAM disappeared above 35 degrees C due to restricted motion of PNIPAM. Generation of singlet oxygen (O-1(2)) from the C-60/P98N100 complex by photo-irradiation was confirmed using 9,10-anthracene dipropionic acid (ADPA). The absorbance of ADPA decreased with increasing irradiation time due to oxidation of ADPA by O-1(2). It is expected that the C-60/P98N100 complex can be applied as a thermo-responsive carrier for photodynamic therapy. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2432-2439