Poly(p-phenylene)-based random copolymers with locally and densely sulfonated multi-phenyl pendants, which are promising candidates for hydrocarbon -based electrolyte membrane materials for fuel cells, were synthesized using Ni(0)-catalyzed cross-coupling polymerization. The synthesized ionomers, SPPFPB-o, showed outstanding dimensional changes and proton conductivity. The SPPFPB-5.5 membrane in particular had the highest ion exchange capacity (IEC) (2.58 meq/g) among the SPPFPB-o series. It exhibited smaller dimensional changes toward the in-plane direction (Delta l) than that of the Nafion (R) 212 membrane, in spite of a higher water uptake (WU) value, which seemed to be derived from the rigid backbone structure. Moreover, the SPPFPB-5.5 membrane showed excellent fuel cell performance and long-term stability comparable or superior to those of Nafion (R) 212 under fully and partially hydrated conditions. (C) 2016 Elsevier B.V. All rights reserved.