(336a) Synthesis and Thermogravimetric Characterization of Poly(styrene-isoprene-styrene): Effects of Sulfonation and Linear Vs Branched Morphology

In this study, poly(styrene-isoprene-styrene) (SIS) were sulfonated and characterized using thermogravimetric analysis as a function of: sulfonation (0-63%), and linear vs branched morphology. Unsulfonated linear and branched SIS have very similar thermal stability (PI degrading at 378°C and PS degrading at 428°C). However, upon sulfonation their thermogravimetric behavior showed the disappearance of the mass at 378°C, and the appearance of an additional mass at 254°C (branched) and 270°C (linear), which could be attributed to sulfonated PS. Since the sulfonation of the PI block lost the elastomeric component of the membranes, physical blends of sulfonated and unsulfonated SIS were casted and analyzed. The thermogravimetric analysis of the linear SIS sulfonated/unsulfonated blends show that the PI block shows-up again for the 75/25 unsulfonated/sulfonated blend, but blends homogeneously for the 50/50 blend. Similar results were obtained for the blends of the branched polymer. Water swelling results normalized with sulfonation are also presented to explain the additional phase segregation obtained for the blends and to confirm that the morphologies of sulfonated linear and branched SIS are very similar despite expected morphological differences. Transport properties are currently measured to evaluate selectivities based on these results.