Perfluorobenzoic acid (PFBA) and perfluorobenzenesulfonic acid (PFBSA) membranes were synthesized from perfluorosulfonyl iodide via novel free-radical substitution reactions. Despite its lower ion-exchange capacity, the PFBA film has proton conductivities typically more than two times higher than PFBSA under various temperatures. For example, at 80 degrees C, PFBA has a proton conductivity of 109.6 mS/cm while the PFBSA membrane is only 44.1 mS/cm in water. The PFBA membrane also shows better performance than PFBSA in a 5 cm(2) PEMFC setting. The formation of unique dimerized/trimerized nano clusters of -CO2H facilitates the hopping of protons across the membrane leading to the higher ion conductivities of PFBA. In addition, free-radical substitution reactions were found to be a general method for grafting aromatics or heteroaromatics to the terminals of fluoropolymer side chains via stable C-C bonds that can tolerate hydrolytic conditions. Such perfluoro-aromatic and perfluoro-heteroaromatic membranes may find applications in numerous fields like chemical, chlor-alkali, electric/electronic, optical, and construction industries. (C) 2016 Elsevier B.V. All rights reserved.