Abstract
Diblock copolymers (PNIPAM m -PNVP n ) composed of poly(N-isopropyl acrylamide) (PNIPAM) and poly(N-vinyl-2-pyrrolidone) (PNVP) with well-defined block lengths were successfully prepared via organotellurium-mediated controlled radical polymerization (TERP). Thermo-responsive association properties in water of the diblock copolymers with different block lengths were characterized. All the diblock copolymers dissolve in water molecularly when the solution temperature is below an aggregation temperature (T a) that is near a lower critical solution temperature (LCST) for the PNIPAM block. Comparing T a between the two diblock copolymers of the same the PNIPAM block lengths (DP = 110), the diblock copolymer with a shorter PNVP block length tends to associate at a lower temperature. On the other hand, the association occurred at a higher temperature for the diblock copolymers with shorter PNIPAM block lengths. When the temperature was raised above T a, PNIPAM m -PNVP n formed aggregates due to hydrophobic interactions between the PNIPAM blocks. PNIPAM m -PNVP n bounds to gold nanoparticles in water through coordination interaction of the PNVP block with Au. The polymer-coated gold nanoparticles indicated a temperature-dependent color change arising from a shift of the maximum wavelength of the plasmon band. PNIPAM m -PNVP n was found to associate with fullerene (C60) and thus C60 can be solubilized in water. The C60 complex formed a core–shell micelle-like aggregate comprising a C60/PNVP hydrophobic core and a thermo-responsive PNIPAM shell. The hydrodynamic radius (R h) of the C60 complex increased with increasing temperature, which was ascribed to the hydrophobic association between dehydrated PNIPAM shells above LCST. The generation of singlet oxygen by photosensitization by the C60 complex was confirmed from photo-oxidation of 9, 10-anthracenedipropionic acid. DNA was cleaved by visible light irradiation in the presence of the C60 complex. There may be a hope for a pharmaceutical application of the C60 complex to cancer photodynamic therapy (PDT).
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