Thermogravimetric characterization of highly sulfonated poly(styrene–isobutylene–styrene) block copolymers: Effects of sulfonation and counter-ion substitution

In this study, poly(styrene–isobutylene–styrene) (SIBS) block copolymers were characterized by thermogravimetry as a function of sulfonation level (53–97%) and counter-ion substitution (Mg2+, Ca2+, Ba2+). Sulfonated samples showed an additional minor loss of mass at approximately 290 ± 2 °C, which was not observed in the unsulfonated polymer. At this temperature, desulfonation or a cleavage reaction of the aromatic carbon–sulfur bond occurs. The counter-ion substituted membranes did not show the degradation temperature at 290 °C, but additional unique degradation temperatures above 500 °C, suggesting improved thermal stability for the ionically cross-linked polymer with cations. Some cations (Mg2+, Ca2+, Ba2+), showed multiple high temperature degradations, which suggest that different cross-linked structures are formed throughout the phase segregated morphology.