Ionomers for proton exchange membrane fuel cells with sulfonic acid groups on the end groups: Novel linear aromatic poly(sulflde-ketone)s

The first examples of branched wholely aromatic polymers polyether ketones (PEK) bearing clusters of sulfonic acid groups only on the end groups are presented. The key end group with pensant phenyl group as selective post-sulfonation sites, 1-(4-Hydroxyphenyl)-2,3,4,5,6-pentaphenylbenzene was successfully synthesized via Diels-Alder reaction of 1-methoxy-4-(2- phenylethynyl)benzene and 2,3,4,5-tetraphenylcyclopenta-2,4-dien-1-one, followed by the deprotection of methoxy group by the use of boron tribromide. High molecular weight was obtained under highly concentrated conditions at 150°C in 1-methyl-2-pyrrolidinone (NMP) to minimize the formation of macrocyclic oligomers. The results show that proton conductivity of the sulfonated PSKs was higher for membranes with low ion exchange capability (IEC).