Poly(ether ketone)s bearing pendent sulfonate groups (SPEK-x/y/z) have been successfully synthesized via copolyacylation of a presulfonated monomer SBP and two isomeric AB-type self-condensable comonomers, that is, 4-phenoxybenzoic acid (p-POBA) and 3-phenoxybenzoic acid (m-POBA). Proton-exchange membranes (PEMs) with precisely controlled ion-exchange capacity (IEC) and high strength can be readily prepared from these ionomers. PEMs prepared from p-POBA other than m-POBA exhibit much higher dimensional stability and proton conductivity at elevated temperature above 60 degrees C, showing prominent isomeric (para vs. meta) effects of polymer structural units. Furthermore, properties of PEMs prepared from p-POBA are optimized by tuning IEC. SPEK-1.0/2.2/0 with an IEC of 1.84 mmol g(-1) exhibits acceptable swelling, much higher proton conductivity, and lower methanol permeability than commercial Nafion 115, implying potential application in direct methanol fuel cells. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 200-207