Pulse radiolysis investigation of · OH and · H radicals initiated degradation reaction of sulfonated aromatics as model compounds for proton exchange membrane

Abstract

In order to predict ·OH and ·H radicals initiated degradation of proton exchange membrane (PEM) based on polymers obtained by radiation-induced grafting of styrene or α-methylstyrene on different polyolefin, isopropyl benzene sulfonic acid (IPBS) and tert-butyl benzene sulfonic acid (TBBS) were taken as model compounds for PEM with and without α-H, respectively. Results indicated that ·OH radicals played a vital role in PEM degradation. Eighty-nine percent of ·OH radicals reacted with IPBS to form benzylic radicals by electron transfer and subsequent deprotonation reactions. Benzylic radicals can react with O2 to form peroxyl radicals, which leads to PEM degradation. TBBS, without α-H, reacted with ·OH or ·H radicals, benzylic radicals would not be generated, and only adducts were formed. Adducts have less influence on the stability of TBBS than benzylic radicals. In this work, we elucidated that PEM, without α-H, with similar structures to TBBS, had a stronger resistance to oxidative degradation than PEM with α-H, with similar structures to IPBS.