membranes for application in polymer electrolyte membrane fuel cells are prepared via Colon's Nickel catalyzed cross-coupling reaction. Their chemical stabilities and proton transport abilities are examined as functions of ion-exchange capacity (IEC) and hydrophilic (sulfonated phenylene) and hydrophobic (arylene ether sulfone) block lengths. The membranes show well-defined phase separation and proton conductivities comparable to or exceeding that of a reference Nafion membrane. Block length is positively correlated with conductivity and oxidative stability; SmPPES10–2.0 showed conductivities of 0.11 and 0.13 S/cm in water at 25 °C and 80 °C (90% relative humidity), respectively, and those of SmPPES5-2.0 were 0.10 and 0.11 S/cm, respectively. The SmPPES membrane oxidative stabilities (determined by Fenton's oxidative tests and peroxide exposure tests) are superior to those of conventional poly(arylene ether) membranes because of their sulfonated phenylene blocks. At 80 °C and 100% relative humidity, the optimal SmPPES membrane (IEC = 2.5 meq/g) delivers a current density of 1.5 A/cm2 at 0.6 V (hydrogen/air) and a high-frequency resistance of 38 mΩ cm2, outperforming the reference Nafion NR211 membrane. This control over sulfonated phenylene and ether sulfone hydrophobic blocks provides new insight into designing high-performance polymer electrolyte membranes.