Poly(vinyl chloride) (PVC) is occasionally discolored yellow or red by the formation of polyene chains in the polymer backbone. It has been noted that the formation of such polyene structures is caused by dehydrochlorination of the PVC, accelerated by tertiary amines. Thus, in the present study, we investigated the influence of amines on the formation of polyene structures in PVC, using resonance Raman spectroscopy. The amount of polyene produced by thermal treatment with amine vapor exposure was determined based on the resonance Raman intensity ratio of the polyene band to the PVC band. The results showed that the discoloration of PVC, indicating the formation of polyene structures, was most prominently caused by 1,4‐diazabicyclo[2.2.2.]octane (DABCO), bis(2‐dimethylaminoethyl)ether (BDMEE), or N,N,N′,N′‐tetramethyl‐1,6‐diaminohexane (TMDAH), because of their high basicity and nucleophilicity. In addition, the formation of polyene structures was inhibited by the co‐presence of amine and protic solvent (water, ethanol, and 2‐propanol) or additives containing hydroxyl groups (glycerin, poly[vinyl alcohol]), suggesting that amine nucleophilicity toward PVC is reduced by the protonation of amine to lone pairs of tertiary amines. J. VINYL ADDIT. TECHNOL., 26:253–258, 2020. © 2019 Society of Plastics Engineers

中文翻译：

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叔胺对聚氯乙烯热降解的促进和抑制作用

聚氯乙烯（PVC）有时会在聚合物主链中形成多烯链而变黄或变红。已经注意到，这种多烯结构的形成是由PVC的脱氢氯化作用引起的，叔胺促进了脱氯化氢作用。因此，在本研究中，我们使用共振拉曼光谱研究了胺对PVC中多烯结构形成的影响。基于多烯带与PVC带的共振拉曼强度比，确定通过胺蒸气暴露进行热处理而产生的多烯的量。结果表明，PVC的变色是多烯结构的形成，最主要的原因是1,4-二氮杂双环[2.2.2。]辛烷（DABCO），双（2-二甲基氨基乙基）醚（BDMEE）或N ，N，N'，N'-四甲基-1,6-二氨基己烷（TMDAH），因为它们具有很高的碱性和亲核性。此外，胺和质子溶剂（水，乙醇和2-丙醇）或含有羟基的添加剂（甘油，聚乙烯醇）的共存会抑制多烯结构的形成，表明胺对PVC通过胺的质子化作用还原成孤对的叔胺。J.乙烯基添加物。TECHNOL。，26：253–258，2020.©2019塑料工程师协会 乙烯基添加剂。TECHNOL。，26：253–258，2020.©2019塑料工程师协会 乙烯基添加剂。TECHNOL。，26：253–258，2020.©2019塑料工程师协会