Effects of hydrophilic groups of polymer on change in hydrogen-bonding structure of water in hydrogels during dehydration

• Effects of polymer hydrophilicity on water structure in hydrogels were investigated. • Relative amounts of three types of water depend on polymer hydrophilicity. • Structure of bound water changes with hydrophilicity of polymer side chain. • Hydrophilicity is an important factor for dehydration and absorption in hydrogels. To investigate the effects of polymer hydrophilicity on hydrogen-bonding structures of water in hydrogels, differential scanning calorimetry and X-ray diffraction measurements were performed. The results show that the amount of intermediate water in polyacrylamide (PAA) hydrogel is about 12 % smaller than that in poly- N , N ’-dimethylacrylamide (PDMAA) hydrogel. Furthermore, it was found that the bound water in PAA hydrogel primarily exists around the surface of the polymer bundles, whereas that in PDMAA hydrogel acts as a crosslinker between polymer chains. These results suggest that the polymer hydrophilicity is an important factor for dehydration and water absorption in hydrogels.