PROTON-EXCHANGE MEMBRANES BY RADIATION GRAFTING OF STYRENE ONTO FEP FILMS .1. THERMAL-CHARACTERISTICS OF COPOLYMER MEMBRANES

Thermal behavior of radiation-grafted and sulfonated fluoroethylene-he xafluo-ropropylene)-g-polystyrene membranes was evaluated using thermo gravimetric analysis. A three-step degradation pattern was observed fr om thermograms of all the membranes and was attributed to the dehydrat ion, desulfonation, and degradation of the FEP backbone. The evidence for desulfonation was reflected in the loss in ion exchange capacity o f the heat-treated samples. The membranes were found to undergo loss i n ion exchange capacity beyond approximate to 200 degrees C. No trace of sulfonic acid groups as the ion exchange sites was found above appr oximate to 350 degrees C. The swelling of heat-treated membranes was a lso reduced considerably. However, the loss in swelling was much highe r than that in the ion exchange capacity of the corresponding membrane . The results were explained in terms of cross-linking reaction occurr ing in the membrane matrix during the desulfonation process that impar ts rigidity in the membrane matrix. (C) 1993 John Wiley and Sons, Inc.