Thermogravimetric characterization of polystyrene-based, triblock copolymers: effects of sulfonation, counter-ion substitution, number average molecular weight, and polystyrene weight fraction

Abstract

In this study, poly (styrene-isobutylene-styrene) (SIBS) was characterized using thermogravimetric analysis. The thermal behavior of three types of SIBS, with different average number molecular weight, Mn , and polystyrene weight percent, are discussed as a function of sulfonation level and substitution with different ions (Ba+2, Ca+2, and Mg+2). For unsulfonated samples, a decrease in the degradation temperature was observed with an increase in Mn, for 30 % polystyrene by weight. Also, a decrease in the degradation temperature was observed with an increase in percent polystyrene with Mn of 100,000 g/mol. At high sulfonation levels, the backbone degradation temperature of the studied polymers increased up to a constant value, suggesting morphological similarities. The weight loss stage corresponding to the degradation of sulfonic groups was not observed in sulfonated polymers cross-linked with cations; however, two new weight loss stages are observed, which are attributed to the loss of cations and sulfonic groups. They are lost in two stages due to different coordination of the cations. SIBS with 15 % polystyrene by weight and Mn of 100,000 g/mol has a higher polymer backbone degradation temperature when compared to the other two studied SIBS, thus it can be considered more thermally stable.