Chitosan was modified with polyacrylonitrile (PAN) through ceric-initiated graft copolymerization. The chitosan-g-PAN product was saponified using sodium hydroxide aqueous solution to prepare a novel superabsorbent hydrogel, H-chitoPAN. Duration of completing the saponification reaction as well as the water absorbency capacity of the hydrogel was decreased with increasing the alkaline concentration. Either chitosan-g-PAN or H-chitoPAN was characterized by FTIR spectroscopy and DSC, TGA, and DTG thermal methods. According to FTIR, all the nitrile groups were converted to carboxylate and carboxamide groups. Both modified chitosans exhibited enhanced thermal stability over chitosan. The H-chitoPAN superabsorbent hydrogel was recognized to be highly responsive to pH. Study of net effect of H+/OH- concentration (in absent of buffer solution) showed several sharp and large volume changes vs small pH variation in the range of 2-13. This abrupt swelling behavior was explained based on variety of pH-dependent interactions of functional groups incorporated in the gel network by an external pH modulation. (C) 2003 Wiley Periodicals, Inc.