As a novel class of proton exchange membrane (PEM) materials for application in fuel cells, sulfonated poly(arylene ether ketone)s (SPAEK-BPs) were prepared by polycondensation via a nucleophilic substitution reaction followed by post-sulfonation. In this way, SPAEK-BPs with different degrees of sulfonation (DS) were quantitatively synthesized via the use of chlorosulfonic acid as the sulfonating agent. It was discovered that only one sulfonic acid group can be selectively introduced without degradation per each repeating unit of polymer due to requirements for controlling reaction conditions such as reaction time and temperature. In this study, the experimentally observed DS were close to the theoretical values expected from the monomer ratios. The glass transition temperatures (T-g's) and decomposition temperatures (T-d's) of the polymers varied from 167 to 213 and 298 to 343 degrees C, respectively. In addition, the proton conductivities of the SPAEK-BP membranes exhibited up to a maximum of about 0.083 S/cm at 25 degrees C and 0.098 S/cm at 80 degrees C. (C) 2008 Elsevier B.V. All rights reserved.