Locally and Densely Sulfonated Poly(ether sulfone)s as Proton Exchange Membrane

New locally and densely sulfonated poly(ether sulfone)s were successfully prepared for fuel cell applications by the nucleophilic substitution of 4,4′-dichlorodiphenylsulfone with 1,2,4,5-tetrakis([1,1′-biphenyl]-2-oxy)-3,6-bis(4-hydroxyphenoxy)benzene and 2,2-bis(4-hydroxyphenyl)hexafluoropropane, followed by sulfonation using chlorosulfonic acid. The polymers gave tough, flexible, and transparent membranes by solvent casting. The large difference in polarity between the locally and densely sulfonated units and hydrophobic units of the polymers resulted in the formation of well-defined phase-separated structures, which induced efficient proton conduction in a wide range of 30−95% RH at 80 °C.