Hydrogel materials were synthesized by radical copolymerization of 2-hydroxyethyl methacrylate (HEMA)、N-vinylpyrrolidone (NVP) and n-butyl methacrylate(BMA)/methyl methacrylate(MMA)

with azobisisobutyronitrile (AIBN) as an initiator.The different states of water in swelling hydrogels were studied by means of differential scanning calorimetry (DSC) combined with thermogravimetry (TG).It was found that water in polymer existed in three states:freezing free water

freezing bond water and non-freezing bond water. DSC and TG data show that the content of freezing water in hydrogel increased with the growth of NVP percentage

and the non-freezing water in hydrogel increased with the growth of HEMA and n-butyl methacrylate(BMA)/methyl methacrylate(MMA) percentages.The tensile properties of the material increased with adding the hydrophobic monomers. The plasticization of the material was affected by the non-freezing water in hydrogel rather than by the freezing water.