Studies on the states of water and sodium ions in poly(N-isopropylacrylamide) gel

The state of water and sodium ions in poly(N-isopropylacrylamide) gel were studied by differential scanning calorimetry (DSC), and H-1 and Na-23 NMR. The motional stare of water in the gel is restricted at the phase transition point. DSC and H-1 NMR suggest that the associated water is considered to be transformed into nonfreezing water on increasing the volume fraction of the polymer. Na-23 NMR indicates that the sodium environment is distorted at higher temperatures, leading to an increase for the bound values of both linewidth and chemical shift, which is consistent with the finding that the introduction of Na+ ions into a hydrated gel system increases the amount of nonfreezing water.