The influence of sulfonation degree on the thermal behaviour of sulfonated poly(arylene ethersulfone)s

Initial decomposition temperature (T_i), apparent activation energy of degradation (E_a) and glass transition temperature (T_g) of some low molar mass (M_n ≈ 8000 g mol⁻¹) sulfonated poly(arylene ethersulfone)s s-(PAES)s were determined to check their dependence on sulfonation degree (SD). The results obtained were compared with those for unsulfonated poly(arylene ethersulfone) PAES. In order to have an accurate control of the chemical structure, a pre-sulfonation route was followed for the preparation of sulfonated compounds. The thermal behaviour of the investigated s-(PAES)s as well as that of PAES appears not to be influenced by the environment (flowing nitrogen or static air atmosphere) of degradation. Both T_i and T_g values of s-(PAES)s were higher than those of PAES and increased quite linearly as a function of sulfonation degree. An analogous linear trend was observed for the apparent degradation energy of s-(PAES)s, but the values found were largely lower than those of unsulfonated homopolymer. The results are discussed and interpreted.