Thermal analysis of sulfonated polymers tested as polymer electrolyte membrane for PEM fuel cells

An aromatic polymer, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was sulfonate with different sulfonation degrees (30, 50, and 75?% theoretical degree) to obtain an electrolytic polymer suitable as proton exchange membrane for fuel cells. Thermal behaviors of sulfonated PPO were tested by differential scanning calorimetry and thermogravimetry. The sulfonation degrees were correlated with glass transitions temperatures (T _g) and the percent of weight loss. One notices a good fitting between sulfonation degree and the percent of weight loss thanks splitting of sulfonic moieties but it is not the same for glass transition temperatures that have a random variation.