Novel sulfonated poly(ether ether ketone)/phosphonated polysulfone polymer blends for proton conducting membranes

Phosphonated polysulfones in the acid form (PPSU-As) with degree of phosphonation (DP) = 0.4, 0.75, and 0.96 were successfully synthesized and utilized for the preparation of polymer blend with sulfonated poly(ether ether ketone) (SPEEK) having a degree of sulfonation (DS) = 75. The resulted blend membranes were characterized and investigated as new polyelectrolyte membrane for fuel cells applications. SPEEK/PPSU-A blend membranes formed ionic networks through hydrogen bonding bridges between the strong sulfonic acid groups and the amphoteric phosphonic acid groups. These ionic interactions resulted in enhanced membrane properties in terms of water swelling, methanol uptake, methanol permeability, mechanical strength, and thermal stability, without significant loss of proton conductivity. All the blend membranes were transparent to visible light with presence of microphases in the order of 10-20 nm. When compared to parent SPEEK membranes, the new SPEEK/PPSU-A blend membranes showed slightly lower methanol permeability compared to neat SPEEK membrane. Membranes with 30 wt% phosphonic acid content with DP = 0.75 and 0.96, exhibited slightly higher proton conductivities at temperatures above 50 °C in comparison with Nafion membrane.