Development of multiblock copolymers with novel hydroquinone-based hydrophilic blocks for proton exchange membrane (PEM) applications

Hydrophilic–hydrophobic sequenced multiblock copolymers were synthesized and evaluated for use as proton exchange membranes (PEMs). The multiblock copolymers were prepared by a coupling reaction between fully disulfonated hydroquinone-based hydrophilic oligomers (HQS100) and unsulfonated poly(arylene ether sulfone) hydrophobic oligomers (BPS0). The hydroquinone-based hydrophilic oligomers possess several advantages over previously utilized biphenol-based hydrophilic oligomers (BPS100), including higher hydrophilicity, enhanced nano-phase separation with hydrophobic segments, and lower cost. To maintain the hydrophilic–hydrophobic sequences in the system, the coupling reactions were conducted at low temperature (e.g., 105 °C) to avoid ether–ether exchange reactions. The coupling reaction was solvent sensitive due to a low reactivity of the hydroquinone-phenoxide end-group on the HQS100. All copolymers produced tough ductile films when cast from an NMP or DMF solution. Fundamental membrane parameters including water uptake, proton conductivity, and swelling ratio were investigated along with morphology characterizations by atomic force microscopy (AFM).