New insights into the mechanism of amine/nitroxide cycling during the hindered amine light stabilizer inhibited oxidative degradation of polymers

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DOIResolve DOI: http://doi.org/10.1021/ja3006379
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TypeArticle
Journal titleJournal of the American Chemical Society
ISSN0002-7863
1520-5126
Volume134
Issue31
Pages1297912988; # of pages: 10
AbstractHigh-level ab initio molecular orbital theory calculations are used to identify the origin of the remarkably high inhibition stoichiometric factors exhibited by dialkylamine-based radical-trapping antioxidants. We have calculated the free energy barriers and reaction energies at 25, 80, and 260 °C in the gas phase and in aqueous solution for a broad range of reactions that might, potentially, be involved in amine/nitroxide cycling, as well as several novel pathways proposed as part of the present work, including that of N-alkyl hindered amine light stabilizer activation. We find that most of the literature nitroxide regeneration cycles should be discarded on either kinetic or thermodynamic grounds; some are even inconsistent with existing experimental observations. We therefore propose a new mechanistic cycle that relies on abstraction of a β-hydrogen atom from an alkoxyamine (R¹R²NOCHR³R⁴). Our results suggest that this cycle is energetically feasible for a range of substrates and provides an explanation for previously misinterpreted or unexplained experimental results. We also explore alternative mechanisms for amine/nitroxide cycling for cases where the alkoxyamines do not possess an abstractable β-hydrogen.
Publication date
LanguageEnglish
AffiliationSecurity and Disruptive Technologies; National Research Council Canada
Peer reviewedYes
NPARC number21269007
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Record identifier109a7c2b-8af6-400f-9b80-116a54aacccb
Record created2013-11-29
Record modified2016-05-09
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