Ionomers for proton exchange membrane fuel cells with sulfonic acid groups on the end‐groups: Novel branched poly(ether‐ketone)s with 3,6‐ditrityl‐9<i>H</i>‐carbazole end‐groups

Abstract

Branched wholly aromatic poly(ether-ketone)s (PEKs) bearing clusters of sulfonic acid groups on a novel end-group, 3,6-ditrityl-9H-carbazole, were synthesized by the polycondensation of activated aromatic difluorides and 4,4′-dihydroxybenzophenone in the presence of the above end-group and trifunctional branching agent, 1,3,5-tris(4-(4-fluorophenylsulfonyl)phenyl)benzene, followed by postsulfonation to introduce up to 8 sulfonic acid groups on each endgroup in PEKs. PEMs of these sulfonated branched PEKs with the same level of IECs (0.99–1.25 mequiv./g) as Nafion® (0.91 mequiv./g) showed proton conductivities (66–95 mS/cm) comparable to that (98 mS/cm) of Nafion®®. TEM analysis showed significantly phaseseparated, and worm-like, highly connected morphology in the PEK membranes.