N-vinyl pyrrolidone(NVP) grafted chitosan(CHI) hydrogels were prepared.The influences of main factors such as mass ratio of NVP∶CHI

initiator content

crosslinking agent content

polymerization temperature and acetic acid concentration on the grafting ratio and swelling property of hydrogels were discussed.Grafting ratio was up to above 300% when mass ratio of NVP to CHI was about 6.The swelling behavior of the hydrogels was studied at different temperatures

pH values and NaCl concentration of swelling mediums.It was found that the swelling ratio of the hydrogels was high when pH value was about 7.Some hydrogels showed temperature sensitivity，had ultimate equilibrium swelling ratio at about 40 ℃ and the first grade phase transition was observed. NVP grafted CHI hydrogels showed anti-polyelectrolyte effect in NaCl solution.The swelling kinetics of hydrogels was investigated with the Fick model.It was suggested from the results that swelling belonged to the non-Fick model when CHI content was above 30% and it was influenced greatly by some other factors such as relaxation

contraction of hydrogel net

interaction between solute molecular and some groups on the polymer net

interaction between polymer chain

except free diffusion of water molecules while swelling belonged to the Fick model when CHI content was lower.