Experimental evidences regarding the sulfonation of polyoxadiazole and oxadiazole-triazole copolymers during the preparation are given. The structures of the polymers were qualitatively and quantitatively characterized by elemental analysis, H-1 NMR, and FTIR. Polymers with high molecular weights (up to 470,000 g/mol) exhibiting highly oxidative stability are obtained allowing the casting of mechanically stable membranes with high storage modulus (about 4 GPa at 100 degrees C) and high proton conductivity values (order of magnitude of 10(-2) S cm(-1) at 80 degrees C). (C) 2007 Elsevier B.V. All rights reserved.