Improved performance of novel sulfonated poly(arylene ether sulfone) copolymer via tethering densely sulfonated pendant groups

Abstract

A novel monomer with tethering multiple pendant ionizable methoxy groups, 1-(2,6-difluorophenyl)-2-(2′-methoxy-3,3″,5,5″-tetramethoxy [1,1':3′,1″-terphenyl]-5′-yl)-1,2-ethanedione (DFTMTE), are synthesized and utilized to prepare poly (arylene ether sulfone)s. The copolymers tethering densely sulfonated pendant groups are then obtained via the process of demethylation and nucleophilic substitution. The sulfonated copolymer membranes having ion exchange capacity (IEC) in the range of 1.72–2.64 mequiv. g−1 exhibit high conductivity (215–379 mS cm−1) at 80 °C. The maximum power density is in the range of 1660–1870 mW cm−2, which is significantly higher than that exhibited by commercially available Nafion 212 membranes (117 mS cm−1 and 1350 mW cm−2) under the same condition. The improved performance is ascribed to the excellent microphase separation exhibited by these materials, resulting from the densely sulfonated pendant groups and side-chain copolymer structures. Quinoxaline-based crosslinking helps achieve a better balance among the properties of the membranes. The crosslinked membrane CSP-1 (IEC of 1.72 mequiv. g−1) exhibits high conductivity (215 mS cm−1), low membrane swelling (<11%) at 80 °C, high maximum power density (1660 mW cm−2), and good stability of the corresponding membrane electrolyte assembly, which reveals a high potential for fuel cell applications.