The degradation mechanism of sulfonated poly(arylene ether sulfone)s in an oxidative environment

The degradation of sulfonated aromatic hydrocarbons based polymer electrolyte membranes is an important issue for fuel cell stability. However, its mechanism is relatively unclear. We have conducted accelerated radical tests and degradation product analysis for various sulfonated poly(arylene ether sulfone) (SPES) compounds. We evaluated the chemical durability of SPES, and observed its degradation mechanism under oxidative attack by hydrogen peroxide. Various SPES compounds were synthesized from 4,4′-biphenol, 4,4′-dihydroxy diphenyl sulfone, and 4,4′-dihydroxy benzophenone comonomers, and their physical properties were evaluated. SPES copolymerized with 4,4′-dihydroxy diphenyl sulfone had a higher durability towards oxidative attack compared with the other compounds studied, and SPES copolymerized with 4,4′-dihydroxy benzophenone exhibited the lowest durability. Moreover, fitting the numerical simulation data to chromatograms obtained from gel permeation chromatograms showed that while the polymers underwent an unzipping (edge) scission during oxidative attack, polymers with a lower chemical durability had a higher midpoint scission rate than did polymers with a higher chemical durability.