ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, School of Chemistry, University of Wollongong, Wollongong, NSW 2522, Australia.
BlueScope Steel Research, PO Box 202, Port Kembla, NSW 2505, Australia.
Anal Chim Acta. 2014 Jan 15;808:190-8. doi: 10.1016/j.aca.2013.09.039. Epub 2013 Oct 1.
Changes in the molecular structure of polymer antioxidants such as hindered amine light stabilisers (HALS) is central to their efficacy in retarding polymer degradation and therefore requires careful monitoring during their in-service lifetime. The HALS, bis-(1-octyloxy-2,2,6,6-tetramethyl-4-piperidinyl) sebacate (TIN123) and bis-(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate (TIN292), were formulated in different polymer systems and then exposed to various curing and ageing treatments to simulate in-service use. Samples of these coatings were then analysed directly using liquid extraction surface analysis (LESA) coupled with a triple quadrupole mass spectrometer. Analysis of TIN123 formulated in a cross-linked polyester revealed that the polymer matrix protected TIN123 from undergoing extensive thermal degradation that would normally occur at 292°C, specifically, changes at the 1- and 4-positions of the piperidine groups. The effect of thermal versus photo-oxidative degradation was also compared for TIN292 formulated in polyacrylate films by monitoring the in situ conversion of N-CH3 substituted piperidines to N-H. The analysis confirmed that UV light was required for the conversion of N-CH3 moieties to N-H - a major pathway in the antioxidant protection of polymers - whereas this conversion was not observed with thermal degradation. The use of tandem mass spectrometric techniques, including precursor-ion scanning, is shown to be highly sensitive and specific for detecting molecular-level changes in HALS compounds and, when coupled with LESA, able to monitor these changes in situ with speed and reproducibility.
聚合物抗氧化剂（如受阻胺光稳定剂（HALS））的分子结构变化是其延缓聚合物降解功效的核心，因此需要在其使用寿命期间进行仔细监测。HALS，双（1-辛氧基-2,2,6,6-四甲基-4-哌啶基）癸二酸酯（TIN123）和双（1,2,2,6,6-五甲基-4-哌啶基）癸二酸酯（TIN292），被配制成不同的聚合物体系，然后暴露于各种固化和老化处理中，以模拟实际使用情况。然后直接使用液萃取表面分析（LESA）与三重四极杆质谱仪联用分析这些涂层的样品。分析交联聚酯中 TIN123 的结果表明，聚合物基质保护 TIN123 免受通常在 292°C 下发生的广泛热降解，特别是哌啶基团的 1-和 4-位的变化。还通过监测原位 N-CH3 取代的哌啶转化为 N-H，比较了 TIN292 在聚丙烯酸酯薄膜中热降解与光氧化降解的影响。分析证实，需要紫外线才能将 N-CH3 部分转化为 N-H-这是聚合物抗氧化保护的主要途径-而热降解则不会观察到这种转化。串联质谱技术（包括前体离子扫描）的使用显示出对检测 HALS 化合物分子水平变化具有高度的灵敏度和特异性，并且当与 LESA 结合使用时，能够以速度和重现性原位监测这些变化。
