Synthesis and Swelling Behavior Analysis of Poly(acrylamidoxime‐co‐2‐acrylamido‐2‐methylpropane Sulfonic Acid) Hydrogels

Abstract

An investigation of water uptake behavior of a novel poly(acrylonitrile‐co‐2‐acrylamido‐2‐methylpropane sulfonic acid‐co‐N,N′‐methylenebisacrylamide) hydrogel system was carried out with two major objectives. First, the study was initiated to understand the effect of various synthesis conditions, i.e., reaction temperature, initiator content, crosslinker content and pH,on the water absorbency of resulting hydrogels. The second reason was to evaluate these hydrogels after reaction with hydroxylamine hydrochloride to convert the CΞN (nitrile) groups to ‐C˭N‐OH (amidoxime) groups. The optimum amidoximation conditions was determined. The structure of the hydrogels, before and after amidoximation, was analyzed with FTIR and thermal methods. The optimum synthesis temperature, initiator concentration and crosslinker content were found to be 55°C, 1.5 (wt.%) and 1.5 (wt.%), respectively. The equilibrium water uptake increases with an increase in initiator (K2S2O8) concentration and crosslinker (BAAm) content up to 1.5% and then it begins to decrease with a further increase in K2S2O8 and BAAm content. The gel undergoes a drastic volume change in the pH range 5, thus indicating the dissociation of NH groups of acrylamidoxime. The pH increased at 7, and this pH shift may be attributed not only to the acidic region, but also the basic region. A drastic volume change is also observed at pH:10, which may be due to the dissociation of the AMPS SO3H groups. The swelling ratio of the hydrogel sample in sea water, tap water and distilled water are collected. According to the results, the maximum swelling ratio was observed in the distilled water. Finally, the nitrile groups can be easly converted into amidoxime groups via treatment with a solution of hydroxylamine. The swelling behavior of hydrogels are in good agreement, before and after amidoximation.