Branched and cross-linked proton conductive poly(arylene ether sulfone) lonomers: Synthesis and properties

A series of branched and cross-linked poly (arylene ether sulfone) ionomers containing sulfofluorenyl groups, 2b-e were synthesized in order to investigate the effect of these chemical modifications on the properties. Ionomers 2b-e gave a flexible, ductile, and transparent membrane by casting from DMAc solution. The branching and cross-linking were effective to improve the dimensional stability under wet conditions without losing their high thermal, oxidative, and hydrolytic stability. The cross-linked ionomer 2e (IEC = 2.63 meq-g^-1) membrane showed high proton conductivity of 0.2 S · cm^-1 at 87% RH and 0.02 S · cm^-1 at 57% RH. The branched ionomer 2b membrane was durable in proton conductivity for almost 2 months without any chemical degradation.