Highly proton conducting proton-exchange membranes based on fluorinated poly(arylene ether ketone)s with octasulfonated segments

A new bisphenol monomer containing a pair of electron-rich tetra-arylmethane units was designed and synthesized. Based on this monomer, along with commercial 4,4′-(hexafluoroisopropylidene)diphenol A and 4,4′-difluorobenzophenone, a series of novel poly(arylene ether ketone)s containing octasulfonated segments of varying molar percentage (x) (6F-SPAEK-x) were successfully synthesized by polycondensation reactions, followed by sulfonation. Tough, flexible, and transparent membranes, exhibiting excellent thermal stabilities and mechanical properties were obtained by casting. 6F-SPAEK-x samples exhibited appropriate water uptake and swelling ratios at moderate ion exchange capacities (IECs) and excellent proton conductivities. The highest proton conductivity (215 mS cm−1) is observed for hydrated 6F-SPAEK-15 (IEC = 1.68 meq g−1) at 100 °C, which is more than 1.5 times that of Nafion 117. Furthermore, the 6F-SPAEK-10 membrane exhibited comparable proton conductivity (102 mS cm−1) to that of Nafion 117 at 80 °C, with a relatively low IEC value (1.26 meq g−1). Even under 30% relative humidity, the 6F-SPAEK-20 membrane (2.06 meq g−1) showed adequate conductivity (2.1 mS cm−1) compared with Nafion 117 (3.4 mS cm−1). The excellent comprehensive properties of these membranes are attributed to well-defined nanophase-separated structures promoted by strong polarity differences between highly ionized and fluorinated hydrophobic segments. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017