Synthesis and Thermogravimetric Characterization of Poly(styrene-isobutylene-styrene): Effects of Sulfonation, Molecular Weight and Polystyrene Weight Fraction

In this study, poly(styrene-isobutylene-styrene) (SIBS) were sulfonated and characterized using thermogravimetric analysis as a function of: sulfonation (0-84%), molecular weight (Mn) (65K-100K) and polystyrene (PS) weight fraction (15-30%). Sulfonated samples showed an additional loss of mass between 251 and 299°C, which was not observed for the unsulfonated polymers. This additional mass was unique for each polymer studied, suggesting that the different Mn and PS wt fractions created polymers with different thermal stability caused by the location and interconnection of the ionic nanochannels upon sulfonation. This hypothesis is also supported by different water swelling results normalized with sulfonation. In addition, the original backbone degradation temperature was increased upon sulfonation from 392-402°C to 416-451°C for all polymers studied. This increase in degradation temperature for the backbone polymer upon sulfonation was more pronounced for the lower PS wt. fraction (28-58°C) and the higher Mn (58°C). Polymers with 30% PS wt. fraction had similar increase in backbone degradation temperatures (14-18°C) despite significant differences in Mn (65-100K). Transport properties are currently being measured to evaluate selectivities based on these effects.