Preparation and characterization of grafted propane sulfonic acid polyphenylene membrane via superacid-catalyzed reaction

A series of polyphenylene-based polyelectrolytes were synthesized from 2,2ʹ-biphenol, and isatin by superacid catalyzed polyhydroxyalkylation reactions. Grafted sulfonated polyphenylenes were synthesized via K2CO3 catalyzed condensation reaction with 3-bromopropane sulfonic acid potassium salt. These polymers have all carbon–carbon linkages without any ether linkage on polymer backbone, which were not attacked by nucleophiles (H2O, hydrogen peroxide, hydroxide anion and radical). Particularly, chemical modification to flexible sulfoalkyl groups implanted to a biphenol unit afforded better stability due to less reactive towards nucleophilic substitution reaction, and good proton mobility because of well phase separation. The structural properties of the synthesized polymers were investigated by 1H NMR spectroscopy. The membranes were studied by ion exchange capacity (IEC), water uptake, dimensional stability as well as proton conductivity assessment. The chemical degradation test was performed by Fentonʹs reagent, and compared with the usual sulfonated poly(ether sulfone)s and Nafion.