B. Gupta et Gg. Scherer, PROTON-EXCHANGE MEMBRANES BY RADIATION GRAFTING OF STYRENE ONTO FEP FILMS .1. THERMAL-CHARACTERISTICS OF COPOLYMER MEMBRANES, Journal of applied polymer science, 50(12), 1993, pp. 2129-2134
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.