Polymer Electrolyte Membrane Based on Poly(ether sulfone) Containing Binaphthyl Units with Pendant Perfluoroalkyl Sulfonic Acids

A novel poly(ether sulfone) containing binaphthyl units with pendant perfluoroalkyl sulfonic acids (BNSH-PSA) was developed for a polymer electrolyte membrane (PEM). The BNSH-PSA was prepared by the aromatic nucleophilic substitution reaction of 1,1'-binaphthyl-4,4'-diol and 4,4'-dichlorodiphenylsulfone, followed by the bromination with bromine, and then the Ullman coupling reaction with potassium 1,1,2,2,-tetrafluoro-2-(1,1,2,2-tetrafluoro-2-iodoethoxy) ethanesulfonate (PSA-K). The ion exchange capacity (IEC) of BNSH-PSA was estimated to be 1.91 mequiv/g, which corresponded to full conversion to the perfluroalkyl sulfonic acids. The BNSH-PSA membrane prepared by solution casting showed high oxidative and dimensional stability. High proton conductivity comparable to the Nafion 117 membrane was accomplished in the range of 30-95% relative humidity (RH) due to the high acidity of the perfluoroalkyl sulfonic acids. Furthermore, atomic force microscopic observation supported the formation of the phase-separated structure that the hydrophilic domains were well dispersed and connected to each other. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2997-3003, 2011