Synthesis and characterization of pendant propane sulfonic acid on phenylene based copolymers by superacid-catalyzed reaction

• We synthesized sulfonate-grafted polymer for PEMFC.
• Sulfonate-grafted polymer shows good proton conductivity.
• These membranes show good stability in ex-situ degradation test.

A series of phenylene based polyelectrolytes were synthesized from 2,2′-biphenol, biphenyl and isatin by superacid catalyzed polyhydroxyalkylation reactions. Grafted sulfonated polymers were synthesized by substitution reaction with 3-bromopropane sulfonic acid potassium salt. These polymers have all carbon–carbon structure on polymer backbone without ether linkage. Particularly, the flexible sulfoalkyl groups were attached to a 2,2′-biphenol unit and formed grafting structure which afforded better stability due to less reactive towards nucleophilic substitution reaction, and good proton mobility because of well phase separation. The structure properties of the synthesized polymers were investigated by 1H NMR spectroscopy. The membranes were studied by ion exchange capacity (IEC), water uptake, dimensional stability, proton conductivity, and cell performance. The chemical deterioration test was performed by Fenton reagent, and compared with normal sulfonated poly(ether sulfone)s and Nafion.