Synthesis and Studies on Water Swelling Behaviour of Polyacrylamide Hydrogels

Summary The polymerization was carried out under the different concentrations of acrylamide and crosslinker in an aqueous solution of NO2 gas as initiator at 50°C. The resulting polyacrylamide was saponified with NaOH solution. The hydrolysed polymers show high degree of water swelling (>500) than that of unhydrolysed polymers (<100). Swellability of the gel decreases with the increasing concentration of N, N’- methylene bisacrylamide − a crosslinker which enhances the degree of crosslinking in the polymer chains. The increased crosslinking restricts the expansion of polymer network which causes the lowering of the water absorbency. It was observed that polymer hydration increased with the molar mass of polyacrylamide. The swellability of polyacrylamide hydrogels is greatly lowered by the addition of ionic salts in the swelling medium. Both ionic strength and valency of the salts are responsible to decrease the water uptaking capacity of the gels which remain unaffected by nondessociating nature of urea. The hydrogels, so prepared, are stable and quite able to undergo swelling − deswelling cycles suggesting their reversible characters.