Synthesis and property of sulfonated poly(methylisatin biphenylene) containing diphenyl ether by polyhydroalkylation reaction

• We synthesized sulfonated grafting polymer containing diphenyl ether moiety.
• The sulfonic acid was grafted from potassium bromopropansulfonic acid.
• Proton conductivity was controlled by ion exchange capacity.
• Membranes showed good performance with high proton conductivity.

A series of poly(methylisatin biphenylene) were prepared by superacid-catalyzed polyhydroxyalkylation reaction of N-methyl isatin, 2,2′-dihydroxybiphenyl and diphenyl ether. These polymers have some ether linkages on polymer backbone that render softness and make more elastic. And sulfonic acid groups were introduced by sulfonation reaction with potassium-3-bromopropane sulfonic acid. Their sulfonic acid groups with functionalization and the measurement of apposite parameters for proton exchange membranes (PEMs) were described. The membranes showed comparable IEC (1.59–1.98 meq./g), water uptake (32.72–57.30%), proton conductivity (72.1–109.2 mS/cm), and high thermal stability, and also proton conductivity measurement compared with Nafion 211®.