Effect of Solvent on Aggregation Structure and Responsive Properties of Copolymeric Gel with Side Chain Crystals

The copolymeric gel films were prepared by a radical copolymerization of stearyl acrylate(SA), acrylic acid(AA) and N,N′-methylenebisacrylamide(MBAA) as a cross-linking agent. The copolymeric (molar ratio SA/AA/MBAA: 24.7/74.3/1.0) gel films with crystalline side chains were swollen in three different kinds of solvent and their aggregation structure and responsive properties have been investigated. In order to control the SA side chains-solvent interaction and to dissociate carboxyl groups in AA, solvents such as dimethyl sulfoxide (DMSO), (1-hexanol/DMSO) mixed solvents and water with different pH values were used. The responsive behaviors of the (SA/AA/MBAA) gel film swollen in different solvents were discussed on the basis of the weight swelling ratio. The X-ray diffraction study of the gel film revealed that the long period corresponding to a layer distance for the (SA/AA/MBAA) gel film swollen in DMSO increased with temperature or the swelling ratio, and the interchain distance of alkyl side chains remained constant with the variation of temperature up to the melting temperature of SA side chain crystals. The swelling ratio of the gel film in (1-hexanol/DMSO) mixed solvent exhibited an abrupt increase in the case of about 40 wt% of 1-hexanol, because the SA side chain crystals of the gel film in the mixed solvents were dissolved due to an increase in SA-solvent interaction. On the other hand, the gel film in the water with different pH values showed a sharp increase in the swelling ratio above pH = 11, because the ionic repulsive force among the AA groups became greater than the aggregation one among alkyl side chains. These results indicate that the swelling ratio of the (SA/A A/MB AA) gel film can be controlled by temperature, pH and the magnitude of solubility parameter of swelling solvent.