Fabrication and properties of cross-linked sulfonated fluorene-containing poly(arylene ether ketone) for proton exchange membrane

The cross-linkable sulfonated ploy(arylene ether)s derived from 3,3′-diallyl-4,4′-dihydroxybiphenyl, 9,9′-bis(3,5-dimethyl-4-hydroxypheyl)fluorene (DMHPF), 4,4′-difluorobenzophenone (DFBP) and sulfonated 4,4′-diflourobenzophenone (SDFBP) were synthesized over a wide range of DFBP/SDFBP molar ratios. The resulting sulfonated poly(arylene ether)s with high inherent viscosity (0.87–1.46 dl g−1) are soluble in polar organic solvents and can form flexible and transparent membranes by casting from their solution. The cross-linking reaction was carried out using a thermal activated radical cross-linking agent (TARC) at 100 °C. The comprehensive properties of the virgin and the cross-linked membranes were characterized and compared accordingly. The results showed that the cross-linked membranes had better mechanical, oxidative and dimensional stabilities together with high proton conductivity (5.41 × 10−2 S cm−1) at 80 °C under 100% relative humidity when compared with previously synthesized and similar membranes. These improvements were raised from the cross-linking structure and the fabrication procedure of the membranes.