Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich, Switzerland.
Phys Chem Chem Phys. 2013 Apr 14;15(14):4975-83. doi: 10.1039/c3cp44341h.
Poly(α-methylstyrene sulfonic acid) (PAMS) represents a class of polymers that can form the protogenic constituent in electrolyte membranes for fuel cells. Oxidative stress is thought to play an important role in the degradation of the fuel cell membranes. Having previously established that damage may be mediated via abstraction of a benzylic hydrogen, we examined model compounds similar to those used before, but with a methyl group at the α-position. We studied the reaction of HO˙ and SO4(˙-), generated by pulse radiolysis, with model compounds in aqueous solution, and measured k = (2 ± 0.5) × 10(10) M(-1) s(-1) and (2 - 3) × 10(10) M(-1) s(-1) for the reaction of HO˙ with PAMS with average molecular weights of 2640 Da (PAMS-2640) and 6440 Da (PAMS-6440), respectively, at room temperature. At low pH, the decay of the hydroxycyclohexadienyl radical thus formed is accompanied by the formation of an absorption band in the visible region of the spectrum, which we tentatively assign to the radical cation of PAMS-2640 and -6440. The radical cation of PAMS-2640, formed by the reaction of SO4(˙-) with k = (6 ± 1) × 10(8) M(-1) s(-1), has a local absorption maximum at 560 nm, with ε560 ≥ 1400 M(-1) cm(-1). For the reaction of HO˙ and SO4(˙-) with the model compound benzenesulfonate, we measured k = (4-5) × 10(9) M(-1) s(-1) and (1.0 ± 0.3) × 10(8) M(-1) s(-1), respectively, while the reaction of SO4(˙-) with PAMS-6440 proceeds with (0.8-1) × 10(9) M(-1) s(-1). The 4-sulfophenoxyl radical was generated via the reaction of N3˙ with 4-hydroxybenzenesulfonate; ε410 ≥ 2300 M(-1) cm(-1). Not unexpectedly, the radical cation of PAMS is longer-lived than that of polystyrene sulfonic acid. Furthermore, fragmentation may result in desulfonation.
聚（α-甲基苯乙烯磺酸）（PAMS）是一类聚合物，可在燃料电池的电解质膜中形成质子化组成部分。氧化应激被认为在燃料电池膜的降解中起着重要作用。我们之前已经证明，损伤可能是通过夺取苄基氢来介导的，因此我们研究了与之前使用的模型化合物类似的模型化合物，但在α 位具有甲基。我们研究了脉冲辐射解产生的 HO˙和 SO4(˙-)与模型化合物在水溶液中的反应，并测量了室温下平均分子量分别为 2640 Da（PAMS-2640）和 6440 Da（PAMS-6440）的 PAMS 与 HO˙的反应速率常数 k =（2 ± 0.5）×10(10) M(-1) s(-1)和（2 - 3）×10(10) M(-1) s(-1)。在低 pH 值下，由此形成的羟基环己二烯基自由基的衰减伴随着可见光谱中吸收带的形成，我们初步将其分配给 PAMS-2640 和 -6440 的自由基阳离子。通过 SO4(˙-)与 k =（6 ± 1）×10(8) M(-1) s(-1)的反应形成的 PAMS-2640 自由基阳离子，在 560nm 处具有局部吸收最大值，ε560 ≥ 1400 M(-1) cm(-1)。对于 HO˙和 SO4(˙-)与模型化合物苯磺酸盐的反应，我们测量的 k 值分别为（4-5）×10(9) M(-1) s(-1)和（1.0 ± 0.3）×10(8) M(-1) s(-1)，而 SO4(˙-)与 PAMS-6440 的反应以（0.8-1）×10(9) M(-1) s(-1)进行。通过 N3˙与 4-羟基苯磺酸盐的反应生成 4-磺苯氧基自由基；ε410 ≥ 2300 M(-1) cm(-1)。不出所料，PAMS 的自由基阳离子比聚苯乙烯磺酸的自由基阳离子寿命更长。此外，片段化可能导致脱硫。
