Studies on bound water restrained by poly(2-methacryloyloxyethyl phosphorylcholine): Comparison with polysaccharide–water systems

The structural change of water restrained by poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) was investigated by differential scanning calorimetry (DSC), since the biocompatibility of PMPC and related biopolymers is affected by the structure of water on the polymer surface. The phase transition behaviour of PMPC-water systems with a water content (W(c)=mass of water/mass of dry sample, gg(-1)) in the range 0-2.0 was measured in the temperature range -150 to 50 degrees C. Glass transition, cold crystallization and melting were observed. Cold crystallization, which has been suggested as an index of biocompatibility, was detected for PMPC with a W(c) in the range 0.5-0.9. The amounts of two types of bound water, non-freezing water and freezing bound water, were calculated from the melting enthalpy. The amount of non-freezing water of PMPC was approximately 0.48. It was found that the phase transition behaviour and amount of bound water of PMPC were quite similar to those of water-soluble polysaccharide electrolytes. The results indicate that the bound water, not the free water, is restrained by PMPC.