Hydrogels in the form of rods with varying crosslink densities and threedimensional network structures were prepared from Poly(N-vinyl-2-pyrrolidone) (PVP)/ water and PVP/water/persulfate systems by irradiation with ␥ rays at ambient temperature. Average molecular weights between crosslinks, percent swelling, swelling equilibrium values, diffusion/swelling characteristics (i.e., the structure of network constant, the type of diffusion, the initial swelling rate, swelling rate constant), and equilibrium water content were evaluated for both hydrogel systems. Water diffusion to the hydrogel is a non-Fickian type diffusion and diffusion coefficients vary from 6.56 ϫ 10 Ϫ7 to 2.51 ϫ 10 Ϫ7 cm 2 min Ϫ1 for PVP and 6.09 ϫ 10 Ϫ7 to 2.14 ϫ 10 Ϫ7 cm 2 min Ϫ1 for PVP/persulfate hydrogel systems.

Hydrogels in the form of rods with varying crosslink densities and three‐dimensional network structures were prepared from Poly(N‐vinyl‐2‐pyrrolidone) (PVP)/water and PVP/water/persulfate systems by irradiation with γ rays at ambient temperature. Average molecular weights between crosslinks, percent swelling, swelling equilibrium values, diffusion/swelling characteristics (i.e., the structure of network constant, the type of diffusion, the initial swelling rate, swelling rate constant), and equilibrium water content were evaluated for both hydrogel systems. Water diffusion to the hydrogel is a non‐Fickian type diffusion and diffusion coefficients vary from 6.56 × 10−7 to 2.51 × 10−7cm2min−1 for PVP and 6.09 × 10−7 to 2.14 × 10−7 cm2min−1 for PVP/persulfate hydrogel systems. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 994–1000, 2000

Hydrogels with varying cross‐linking densities and average molecular weights between two consecutive cross‐links were prepared from the binary poly(N‐vinyl‐2‐pyrrolidone)/water and ternary poly(N‐vinyl‐2‐pyrrolidone)/water/K2S2O8 systems by irradiation with γ rays at ambient temperature. Both hydrogel systems were employed for diffusion and swelling experiments in various urea solutions at room temperature. Diffusion of urea solutions into hydrogels has been found to be of the non‐Fickian type, except for the samples of PVP/K2S2O8 hydrogels irradiated at higher doses in dilute urea solutions. The percent swelling, equilibrium swelling, initial rate of swelling, swelling rate constant, equilibrium water/urea content, and diffusion constant values were evaluated for PVP and PVP/K2S2O8 hydrogel systems at two different urea concentrations. With regard to swelling data, it was determined that the dilute urea solution can penetrate much more effectively into the PVP/K2S2O8 hydrogel system. © 2000 John Wiley & Sons, Inc. Adv Polym Techn 19: 210–217, 2000

Hydrogels with varying cross-linking densities and average molecular weights between two consecutive cross-links were prepared from the binary poly(N-vinyl-2-pyrrolidone)/water and ternary poly(N-vinyl-2pyrrolidone)/water/K 2 S 2 O 8 systems by irradiation with ␥ rays at ambient temperature. Both hydrogel systems were employed for diffusion and swelling experiments in various urea solutions at room temperature. Diffusion of urea solutions into hydrogels has been found to be of the non-Fickian type, except for the samples of PVP/K 2 S 2 O 8 hydrogels irradiated at higher doses in dilute urea solutions. The percent swelling, equilibrium swelling, initial rate of swelling, swelling rate constant, equilibrium water/urea content, and diffusion constant values were evaluated for PVP and PVP/K 2 S 2 O 8 hydrogel systems at two different urea concentrations. With regard to swelling data, it was determined that the dilute urea solution can penetrate much more effectively into the PVP/K 2 S 2 O 8 hydrogel system.