(188ah) Effect of Sulfonation Level and Counter Ion Substitution On the Proton Conductivity of Poly(styrene-isobutylene-styrene) Membranes

In this study, poly(styrene-isobutylene-styrene) (SIBS), a triblock copolymer, was functionalized with sulfonic groups in order to obtain more selective membranes for gas sensors and fuel cell applications. Sulfonated SIBS was characterized using fourier transform infrared spectroscopy (FTIR) and elemental analysis (EA), to confirm and determine accurate sulfonation levels. Subsequently, the sulfonated polymer was neutralized with three +2 cations: Mg⁺², Ca⁺² and Ba⁺²; to reduce water swelling and create highly selective polymer-metal nanocomposite membranes. Since the potential interconnectivity of the membrane's sulfonic groups is very important for the performance of these dielectric materials, the proton conductivity of the samples was measured. Results show that proton conductivity increases with sulfonation level until a maximum suggesting an optimum ion exchange capacity (IEC) level, while counter ion substitution decreases proton conductivity. Thermogravimetric analysis (TGA) were performed in order to evaluate the thermal stability, which increases with sulfonation level; while counter ion substituted membranes maintained the same degradation temperature. To complement the studies, absorption limitations and their effect on the membrane transport were investigated through water swelling experiments. Although water swelling increases with sulfonation, the effect of metal type will be further discussed.