Terpolymers of ethylene, norbornene, and 5-exo norbornene methyl alcohol are prepared using Pd phosphine sulfonates as catalysts. The pendant hydroxyl groups are then transformed into thioacetate groups. Films cast from the resulting polymers are then oxidized by hydrogen peroxide. This green oxidation method is found to quantitatively transform thioacetate groups into sulfonic acids, leading to the formation of sulfonated hydrocarbon ionomers. These ionomers are thermally stable, exhibit increasing conductivity up to 110 degrees C, and have a low water uptake, indicating that these materials are potentially interesting candidates for the preparation of fuel cell membranes. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 26692676