Copoly(arylene ether)s Containing Pendant Sulfonic Acid Groups as Proton Exchange Membranes

A poly(arylene ether) (PAE) with high fluorine content and a poly(arylene ether nitrile) (PAEN) with high nitrile content, each containing pendant phenyl sulfonic acids were synthesized. The PAE and PAEN were prepared from decafluorobiphenyl (DFBP) and difluorobenzonitrile (DFBN) respectively, by polycondensation with 2-phenylhydroquinone (PHQ) by conventional aromatic nucleophilic substitution reactions. The sulfonic acid groups were introduced by mild postsulfonation exclusively oil the para-position of the pendant phenyl ring in PHQ. The membrane properties of the resulting sulfonated copolymers sPAE and sPAEN were compared for fuel cell applications. The copolymers sPAE and sPAEN, each having a degree of sulfonation (DS) of 1.0 had high ion exchange capacities (IEC,(wet) (volume-based, wet state)) of 1.77 and 2.55 mequiv/cm(3), high proton conductivities of 135.4 and 140.1 mS/cm at 80 degrees C, and acceptable volume-based water uptake of 44.5-51.9 vol % at 80 degrees C, respectively, compared to Nation. The data points of these copolymer membranes are located in the upper left-hand corner in the tradeoff plot of alternative hydrocarbon polyelectrolyte membranes (PEM) for the relationship between proton conductivity versus water uptake (weight based or volume based), i.e., high proton conductivity and low water uptake. Furthermore, the relative selectivity derived from proton conductivity and methanol permeability is higher than that of Nafion.