EFFECT OF SULFONATION LEVEL AND COUNTER ION SUBSTITUTION ON THE PROTON CONDUCTIVITY OF POLY(STYRENE-ISOBUTYLENE-STYRENE) MEMBRANES

摘要

In this study, poly(styrene-isobutylene-styrene) (SIBS), a triblock copolymer, wasfunctionalized with sulfonic groups in order to obtain more selective membranes for gas sensorsand fuel cell applications. Sulfonated SIBS was characterized using fourier transform infraredspectroscopy (FTIR) and elemental analysis (EA), to confirm and determine accurate sulfonationlevels. Subsequently, the sulfonated polymer was neutralized with three +2 cations: Mg+2, Ca+2and Ba+2; to reduce water swelling and create highly selective polymer-metal nanocompositemembranes. Since the potential interconnectivity of the membrane’s sulfonic groups is veryimportant for the performance of these dielectric materials, the proton conductivity of thesamples was measured. Results show that proton conductivity increases with sulfonation leveluntil a maximum suggesting an optimum ion exchange capacity (IEC) level, while counter ionsubstitution decreases proton conductivity. Thermogravimetric analysis (TGA) were performed inorder to evaluate the thermal stability, which increases with sulfonation level; while counter ionsubstituted membranes maintained the same degradation temperature. To complement thestudies, absorption limitations and their effect on the membrane transport were investigatedthrough water swelling experiments. Although water swelling increases with sulfonation, theeffect of metal type will be further discussed.