Synthesis and characterization of partially fluorinated hydrophobic–hydrophilic multiblock copolymers containing sulfonate groups for proton exchange membrane

A new hydrophobic–hydrophilic multiblock copolymer has been successfully synthesized based on the careful coupling of a fluorine terminated poly(arylene ether ketone) (6FK) hydrophobic oligomer and a phenoxide terminated disulfonated poly(arylene ether sulfone) (BPSH) hydrophilic oligomer. ¹⁹F and ¹H NMR spectra were used to characterize the oligomers’ molecular weights and multiblock copolymer's structure. The comparison of the multiblock copolymer ¹³C NMR spectrum with that of the random copolymer showed that the transetherification side reaction was minimized in this synthesis. The morphologies of membranes were investigated by tapping mode atomic force microscopy (AFM), which showed that the multiblock membrane acidified by the high temperature method has sharp phase separation. Membrane properties like protonic conductivity, water uptake, and self-diffusion coefficient of water as a function of temperature and relative humidity (RH) were characterized for the multiblock copolymer and compared with ketone type random copolymers at similar ion exchange capacity value and Nafion^® controls. The multiblock copolymers are promising candidates for proton exchange membranes especially for applications at high temperatures and low relative humidity.