Ni(0)-catalyzed coupling polymerization of 2,5-dichloro-4'-phenoxybenzophenone was investigated by varying the ligand and coligand, temperature, reaction time, and solvent. The weight-average molecular weight (M(w)) of poly(4-phenoxybenzoyl-1,4-phenylene)s (PPBPs) could be controlled by the polymerization conditions and reached a maximum of 4.4 x 10(5) g mol(-1). Sulfonated PPBPs (S-PPBPs) with various M(w)s were prepared with sulfuric acid to study the effect of molecular weight on the chemical and electrical properties of PPBP-based electrolytes. The strong molecular interactions in S-PPBP provided an ion exchange capacity of 2.9 meq g(-1) without loss of high mechanical properties. High molecular weight S-PPBPs had more desirable properties for fuel cell applications. While the swelling ratios and hydration numbers of S-PPBPs decreased with increasing molecular weight, the mechanical strength, proton conductivity, and fuel cell performance increased. S-PPBP also showed anisotropic behavior in the swelling and proton conductivity; such behavior is caused by the rigid-rod nature and the liquid-crystal structure. (C) 2011 Elsevier Ltd. All rights reserved.