Cation exchange membranes by radiation-induced graft copolymerization of styrene onto PFA copolymer films. II. Charactarization of sulfonated graft copolymer membranes

PFA-g-polystyrene sulfonic acid membranes were prepared by simultaneous rad iation-induced graft copolymerization of styrene onto poly(tetrafluoroethyl ene-co-perfluorovinyl ether) (PFA) film followed by sulfonation. The membra ne physicochemical properties such as swelling behavior, ion exchange capac ity, hydration number, and ionic conductivity were studied as a function of the degree of grafting. Thermal as well as chemical stability of the membr anes was also investigated. The membrane properties were found to be mainly dependent upon the degree of grafting. The water uptake, ion exchange capa city, hydration number, and ionic conductivity of the membranes were increa sed, whereas the chemical stability decreased as the degree of grafting inc reased. The membranes showed reasonable physico-chemical properties compare d to Nafion 117 membranes. However, their chemical stability has to be furt her improved to make them acceptable for practical use in electrochemical a pplications. (C) 2000 John Wiley & Sons, Inc.