A series of sulfonated polybenzimidazoles (SPBIs) with varied ion exchange capacities (IECs) have been synthesized by random condensation copolymerization of a new sulfonated dicarboxylic acid monomer 4,6-bis(4-carboxyphenoxy)benzene-1,3-disulfonate (BCPOBDS-Na), 4,4'-dicarboxydiphenyl ether (DCDPE) and 3,3'-diaminobenzidine (DAB) in Eaton's reagent at 140 degrees C. Most of the SPBIs show good solubility in polar aprotic organic solvents such as dimethylsulfoxide (DMSO) and N,N-dimethylacetamide (DMAc). Thermogravimetric analysis (TGA) reveals that the SPBIs have excellent thermal stability (desulfonation temperatures (on-set) > 370 degrees C). The SPBI membranes show good mechanical properties of which tensile strength, elongation at break, and storage modulus are in the range of 89-96 MPa, 12-42%, and 2.4-3.1 GPa, respectively. Moreover, the SPBI membranes exhibit phosphoric acid (PA) uptake in the range of 180-240% (w/w) in 85 wt% PA at 50 degrees C, while high mechanical properties (13-20 MPa) are maintained. The SPBI membrane with 240% (w/w) PA uptake displays fairly high proton conductivity (37.3 mS cm(-1)) at 0% relative humidity at 170 degrees C. The fuel cell fabricated with the PA-doped SPBI membrane (PA uptake = 240% (w/w)) displays good performance with the highest output power density of 0.58 W cm(-2) at 170 degrees C with hydrogen-oxygen gases under ambient pressure without external humidification. (C) 2010 Elsevier B.V. All rights reserved.