Two series of high molecular weight disulfonated poly(arylene ether sulfone) random copolymers were synthesized as proton exchange membranes for high temperature water electrolyzers. These copolymers differ based on the position of the ether bonds on the aromatic rings. One series is comprised of fully para-substituted hydroquinone comonomer and the other series incorporated 25 mole % of a meta-substituted comonomer, resorcinol, and 75 mole % hydroquinone. The influence of the substitution position on water uptake and electrochemical properties of the membranes were investigated and compared to that of the state-of-the-art membrane, Nafion™. Mechanical properties of the membranes were measured for the first time in fully hydrated conditions at ambient and elevated temperatures. Submerged in water, these hydrocarbon-based copolymers had moduli an order of magnitude higher than Nafion™. Selected copolymers of each series showed dramatically increased proton conductivities at elevated temperature in fully hydrated conditions while their H2 gas permeabilities were well controlled over a wide range of temperatures. These improved properties were attributed to the high glass transition temperatures of the disulfonated poly(arylene ether sulfone)s.