Carboxylic acid functionalized TPQSH-COOH-XX copolymers were synthesized to investigate their proton exchange membrane properties. This new series of copolymers was prepared by copolymerization of a COOH moiety containing diphenol monomer, 2-[bis-(4-hydroxy-phenyl)-methyl]-benzoic acid (TP-COOH), with two dihalide monomers, 4,4'-bis(4'-fluoro-3'-trifluoromethylbenzyl)biphenyl (QBF) and 3,3'-disodiumsulfonyl-4,4'-dichlorodiphenylsulfone (SDCDPS), in different mole ratios. The structure of the copolymers (TPQSH-COOH-XX) and of the homopolymer (TPQ-COOH) was analyzed by spectroscopic techniques. The copolymers TPQSH-COOH-XX with different percentage of -SO3H groups showed in TEM images a clear phase separated morphology with ionic clusters of sizes from 5 to 80 nm. All the COOH functionalized ionomer membranes showed good mechanical properties with enhanced oxidative stability and high dimensional stability. The membranes exhibited high water uptake and swelling due to high IEC values (1.38-1.96 mequiv/g) and the presence of COOH groups. The copolymers showed high proton conductivity (55-116 mS/cm at 80 degrees C and 56-112 mS/cm at 90 degrees C) under fully hydrated condition. (C) 2016 Elsevier B.V. All rights reserved.