Star-Shaped Sulfonated Block Copoly(ether ketone)s as Proton Exchange Membranes

New star-shaped sulfonated block copolymers with hydrophilic and hydrophobic segments as arms have been developed. The star-shaped block copolymers were synthesized via the Friedel−Crafts reaction of a trifunctional core with AB monomers using trifluoromethanesulfonic acid, followed by sulfonation using concentrated sulfuric acid. High molecular-weight polymers over 37 000 in number average molecular weight were easily obtained and gave tough and flexible membranes by solvent casting. The membranes showed relatively good dimensional stability despite high water uptake due to their star-shaped structure. Moreover, the star-shaped structure having hydrophilic segments surrounded by hydrophobic segments enabled the achievement of high bound-water content. The membranes showed excellent proton conductivity which was comparable to that of Nafion 117 in the range of 50−95% RH at 80 °C.