An ionically crosslinked polymer network cornposed of chitosan and sodium hexametaphosphate (SHMP) was synthesized to determine their swelling and ascorbic acid release kinetics at various SHMP concentrations. The chitosan/SHMP hydrogels were synthesized using an acetic acid aqueous solution (1% v/v). Ionization constants (pK(b)) of the SHMP were obtained by potentiometric titration. The results show that the SHMP was hydrolyzed in acidic medium forming orthophosphate and trimetaphosphate. The swelling percentages were measured at different swelling media pH's; the higher swelling capacities were for the systems that were swollen in neutral solution. Also, it was studied the ionic crosslinking degree by turbidimetric titration, comparing the electrostatic interactions between the chitosan and the SHMP; the results shows that electrostatic interactions between the amine groups of the chitosan and the anionic groups of the Si-IMP are dependent of the swelling medium pH. The ascorbic acid diffusion inside the hydrogel follows the second law of Fick, and the diffusion coefficients were obtained for different ShIMP concentrations. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 3595-3600, 2010