Water Uptake Behavior of Poly(methacrylamide‐co‐N‐vinyl‐2‐pyrrolidone‐co‐itaconic acid) as pH‐Sensitive Hydrogels: Part I

Abstract

Novel hydrogels composed of the three monomers N‐vinyl‐2‐pyrrolidone, methacrylamide and itaconic acid, have been prepared by free radical aqueous polymerization. The gels demonstrated a sharp pH‐dependent swelling. The gel, when transferred from artificial gastric fluid (SGF,pH1.2) to simulated intestinal fluid (SIF, pH 7.4), underwent a sharp swelling transition from 45±4 to 327±12 percent within an hour. The hydrogels also exhibited swelling‐deswelling cycles, within a response time of nearly one hour, while maintaining structural integrity. The increase in monomer acid concentration caused an enhancement in water uptake in SIF while the swelling was observed to decrease in SGF with acid content. For an optimum initiator concentration 0.22 mM, the synthesized gel showed the highest water uptake. On increasing the diameter from 0.21 to 0.92 cm, the initial rate of water uptake decreased from 2.50 to 1.15 percent per minute. The Tanaka‐Fillmore theory was also verified. The activation energy for the swelling of the sample with 7.54 percent mole fraction of itaconic acid was found to be 19.74 kJmol−1.