SYNTHESIS AND PROPERTIES OF SULFONATED AND CROSS-LINKED POLY[(VINYLIDENE FLUORIDE)-GRAFT-STYRENE] MEMBRANES

Crosslinked proton exchange membranes were prepared by electron beam g rafting of styrene with divinylbenzene, DVB, or bis(vinyl phenyl)ethan e, BVPE, on to paly(vinylidene fluoride), PVDF, followed by sulfonatio n. The area and thickness increase, crystallinity and mechanical prope rties of the membranes were investigated. All these properties were in fluenced by the crosslinker structure and ifs concentration. The cross linkers increase the final degree of grafting. For noncrosslinked memb ranes it was about 80% and with 10% of BVPE crosslinker about 180% aft er 8 hr. The area increase with grafting is very similar for the noncr osslinked membranes and the differently crosslinked membranes, but the crosslinkers reduce swelling for sulfonated membranes swelled in boil ing wafer. DVB reduces swelling move than BVPE. With grafting, the cry stallinity of the PVDF phase decreases; with 20% BVPE the decrease is smallest and with 10% DVB largest. The mechanical properties of the su lfonated swelled membranes decrease with the degree of grafting, for a 20% DVB crosslinked membrane the strength decreases to zero at degree s of grafting higher than 75%. (C) 1998 John Wiley & Sons, Ltd.