Composite proton-conducting hybrid polymers: Water sorption isotherms and mechanical properties of blends of sulfonated PEEK and substituted PPSU

Mechanical properties (elastic modulus, ultimate strength, and elongation at rupture), water sorption isotherms, and chemical diffusion coefficients of water are reported for composite polymers made from a majority polymer (93 wt %), sulfonated (DS = 0.9) poly-ether-ether-ketone (S-PEEK), and a minority polymer (7 wt %), sulfonated (DS = 2) and/or silylated poly-phenyl-sulfone (PPSU). S-PEEK is responsible for proton conductivity of the membranes, whereas the minority component is added to maintain the mechanical and morphological stability. It is shown that the addition of sulfonated PPSU reduces the mechanical strength and leads to important membrane swelling. In contrast, addition of silylated PPSU highly improves the membrane strength and reduces considerably membrane swelling, indicating a suitable strategy to improve polymer electrolytes for PEM fuel cells. The calculated water uptake coefficients and diffusion coefficients are consistent with those of other members of the S-PEEK polymer family.