Abstract
The hydrophobic interaction of amphiphilic copolymers, which contain 2βhydroxyethyl methacrylate(HEMA) and 1vinylβ2βpyrrolidone (VPy), with Methyl Orange (MO) was compared with that of HEMAβacrylamide (AAm) copolymers to deduce the correlation between their complexation ability in a photochromic azo dye and the photoviscosity effect in aqueous copolymer/dye complex solution. On the basis of the dialysis data and fluorometric analysis it appeared that the complexation dependence on HEMA content in the copolymers was due to the hydrophobic interaction between the polymer and the dye. For a comparable HEMA content AAm copolymers bound less MO than VPy copolymers. It was confiied by photoviscosity measurements that the conformation of the complex composed of photochromic azo dye and HEMA copolymer changed reversibly in response to the photoβ and thermal isomerization of the dye. In HEMAβAAm copolymer systems the photoviscosity effect was small compared with that of HEMAβVPy copolymer systems. From these results it was concluded that the complexation ability of polymers due to the hydrophobic interaction was an important factor in producing a large photoinduced conformational change in water.