Thermal stability of proton exchange membranes prepared by grafting of styrene into pre-irradiated FEP films and the effect of crosslinking

The thermal stability of crosslinked ion exchange membranes, prepared by pre-irradiation grafting of styrene into FEP films in the presence of divinylbenzene (DVB) as a crosslinker and subsequent sulfonation of the grafted films, was investigated by thermogravimetry. The formation of different fragments with increasing temperature was monitored by FTIR. Pre-irradiation leads to destabilization of the FEP backbone, showing both earlier depolymerization and substantial redistribution of monomer formation between the two main degradation steps. The presence of DVB had clear effects on the thermal degradation pattern of the sulfonated graft copolymer membrane. Desulfonation occurred at a lower temperature whereas dearomatization was observed to shift to higher temperatures.