Properties of PEMs based on cross-linked sulfonated poly(ether ether ketone)

PEMs prepared from sulfonated poly(ether ether ketone) and cross-linked with simple polyols (ethylene glycol and glycerol), exhibited enhanced strength, stability in hot water and high proton conductivity. The properties and chemical structure of the cross-linked membranes were studied using TGA, 1H NMR and FTIR. These data suggest that ethylene glycol and glycerol molecules do not link neighbouring main chains via sulfonic acid functions, but rather form alcohol–ether oligomers, bonded to –SO3– group and generating an interpenetrating network which interacts with the main chains. The thermal stability of cross-linked membranes is inferior to that of non-cross-linked ones. It is shown that splitting off of the sulfonic acid groups occurring above 200 °C is accompanied by main chain degradation in both initial and cross-linked membranes. The fact that the degradation temperature exceeds 200 °C suggests that this could be a promising and effective approach to cross-linking sulfonated membranes for FC application.