Thermo Stability of Highly Sulfonated Poly(Styrene-Isobutylene-Styrene) Block Copolymers: Effects of Sulfonation and Counter-Ion Substitution

摘要

In this study, poly(styrene-isobutylene-styrene) (SIBS) block copolymers were characterized by thermogravimetry as a function of sulfonation level (53% to 97%) and counter-ion substitution (Mg+2, Ca+2, Ba+2). Sulfonated samples showed an additional minor loss of mass at approx. 290 plus/minus 2 deg. 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 deg. C, but additional unique degradation temperatures above 500 deg. C, which suggests improved thermal stability for the ionically cross-linked polymer with cations. Some cations (Mg+2, Ca+2, Ba+2) showed multiple high temperature degradations, which suggest that different cross-linked structures occur throughout the phase-segregated morphology.