Comparative study on water structures in PolyHEMA and PolyMEA by XRD-DSC simultaneous measurement

We have found that poly(2-methoxyethylacrylate) (polyMEA) has excellent blood compatibility and proposed that the property is due to freezing bound water in the polymer. This water is defined as that which cold-crystallizes at around -45°C in the heating process of differential scanning calorimetry (DSC). In addition, we have already reported that the water in polyMEA is classified into three types, nonfreezing, freezing bound, and free waters, whereas the water in other polymers is just classified into two types: free and nonfreezing waters. (J Biomed Mater Res 68A, 2004, 684) However, the phenomenon observed by DSC is the enthalpy change and is not a direct evidence for crystallization. To confirm coldcrystallization, a comparative investigation of the thermal and crystallographical properties of water in hydrated polyMEA and poly(2-hydroxyethylmethacrylate) (polyHEMA) as a control was carried out using simultaneous measurements by X-ray diffractometer (XRD) and DSC. In addition, the effect of the water content in the polymers on the properties was studied. As for polyMEA, the finding that XRD crystalline peaks appearing in the heating process were assigned to hexagonal ice indicated cold-crystallization. On the other hand, in the case of polyHEMA, the crystal due to ice was formed only in the cooling process, and during the heating process, the growth of crystal ice was not observed.