Synthesis and Characterization of Sulfonated Poly(ether sulfone)s Containing Mesonaphthobifluorene for Polymer Electrolyte Membrane Fuel Cell

The novel sulfonated poly(ether sulfone)s containing mesonaphthobifluorene (MNF) moiety were synthesized and characterized their properties. The prepared polymers have highly conjugated aromatic structure due to the MNF group which is an allotrope of carbon and one atom thick planar sheets of sp²-bonded carbon atoms. Poly(ether sulfone)s bearing tetraphenylethylene on polymer backbone were synthesized by polycondensation and followed intra-cyclization from tetraphenylethylene to form MNF by Friedel-craft reaction with Lewis acid (FeCl₃). The sulfonation was performed selectively on MNF units with conc. sulfuric acid. The structural properties of the sulfonated polymers were investigated by ¹H-NMR spectroscopy. The membranes were studied by ion exchange capacity (IEC), water uptake, and proton conductivity. The synthesized polymer electrolyte membranes showed better thermal and dimensional stabilities owing to the inducted highly conjugated aromatic structure in the polymer backbone. The water uptake of the synthesized membranes ranged from 23∼52%, compared with 32.13% for Nafion 211® at 80 °C. The synthesized membranes exhibited proton conductivities (80 °C, RH 90%) of 74.6∼100.4 mS/cm, compared with 102.7 mS/cm for Nafion 211®.