Morphological investigations of disulfonated poly(arylene ether sulfone)-b-naphthalene dianhydride-based polyimide multiblock copolymers as potential high temperature proton exchange membranes

A major goal of current proton exchange membrane fuel cell research involves developing high temperature membranes that can operate at ∼120 °C and low humidities. Multiblock copolymers synthesized from 100% disulfonated poly(arylene ether sulfone) (BPSH100) and naphthalene polyimide (PI) oligomers may be an alternative. The high temperature behavior of BPSH100–PI multiblock copolymers was evaluated in terms of morphology and water retention and compared to that of BPSH-based random copolymers, Nafion 112, and new recast Nafion (NRE211). Atomic force microscopy (AFM) performed at elevated temperatures with a hot stage demonstrated that at block lengths of ∼15 kg/mol the multiblock copolymers displayed no morphological changes up to 120 °C or even higher. Water desorption was observed to decrease with increasing block length. The copolymers exhibited little to no water loss during a 200 °C isotherm in contrast to random BPSH copolymers and Nafion. A BPSH100–PI multiblock copolymer with large block length appears to have morphological stability and retain water (likely strongly bound) at temperatures exceeding 120 °C, suggesting its candidacy as a high temperature PEM.