Development and Characterization of Highly Conducting Nonfluorinated Di and Triblock Copolymers for Polymer Electrolyte Membranes

To achieve stable polymer electrolyte membranes (PEMs) with efficient ionic nano-channels, novel fully aromatic AB or ABA copolymers composed of poly(fluorenyl ether sulfone biphenyl)s (PFESBs) and poly(arylene ether sulfone)s (PAESs) were synthesized via polymerization and post-sulfonation methods, and were explored as fuel cell membranes. The structural analysis of synthesized copolymers and the corresponding membranes were ascertained by gel permeation chromatography (GPC), Fourier transform infrared (FTIR), and ¹H nuclear magnetic resonance (NMR) techniques. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis showed that the prepared membranes were thermally stable, so that elevated temperature fuel cell operation would be possible. High hydrophilic and hydrophobic nano-phase separation and obvious ionic aggregate block morphology was observed in both triblock and diblock copolymers in atomic force microscopy (AFM) phase images, which may be highly related to their proton transport ability. A sulfonated AB diblock copolymer membrane with an ion-exchange capacity (IEC) of 2.06 meq g⁻¹ has a maximum proton conductivity of 184 mS cm⁻¹, which is higher than that of a perfluorosulfonic acid membrane under the same measurement conditions.