感熱性高分子水溶液の相分離・ゲル化・レオロジー

Abstract

The recent status of studies on temperature–sensitive water-soluble polymers is briefly reviewed. The concept of cooperative dehydration, defined as simultaneous dissociation of the water molecules bound to a polymer chain in correlated sequences, has been applied to study the collapse transition and LCST phase separation of temperaturesensitive polymer, poly(N–isopropylacrylamide), in water and in mixed solvents of water and methanol. The transition becomes sharper as the cooperativity of (de)hydration increases. The sharp depression by the LCST co–nonsolvency in the mixed solvents is shown to be caused by the competitive hydrogen bonding of water and methanol seeking for hydrogen–bonding sites on the polymer chains. The degree of hydration and of methanol binding, preferential adsorption coefficients, LCST cloud–point depression are theoretically calculated and compared with the experiments. The shifts of LCST induced by added salts (salting–in and salting-out effect) are briefly discussed from the viewpoint of competing polymer hydration and ionic hydration, with focus on anion binding.