Ahn Yunho, Colin Xavier, Roma Guido
Université Paris-Saclay, CEA, Service de Recherches de Métallurgie Physique, 91191 Gif sur Yvette, France.
PIMM, Arts et Metiers Institute of Technology, CNRS, CNAM, HESAM University, 151 Boulevard de L'Hôpital, 75013 Paris, France.
Polymers (Basel). 2021 Jun 29;13(13):2143. doi: 10.3390/polym13132143.
Understanding the degradation mechanisms of aliphatic polymers by thermal oxidation and radio-oxidation is very important in order to assess their lifetime in a variety of industrial applications. We focus here on polyethylene as a prototypical aliphatic polymer. Kinetic models describing the time evolution of the concentration of chain defects and radicals species in the material identify a relevant step in the formation and subsequent decomposition of transient hydroperoxides species, finally leading to carbonyl defects, in particular ketones. In this paper, we first summarize the most relevant mechanistic paths proposed in the literature for hydroperoxide formation and decomposition and, second, revisit them using first principles calculations based on Density Functional Theory (DFT). Our results partially confirm commonly accepted reaction energies, but also propose alternative, more favourable, reaction paths. We highlight the influence of the environment-crystalline or not-on the outcome of some of the studied chemical reactions. A remarkable result of our calculations is that hydroxyl radicals play an important role in the decomposition of hydroperoxides. Based on our findings, it should be possible to improve the set of equations and parameters used in current kinetic simulations of polyethylene radio-oxidation.
为了评估脂肪族聚合物在各种工业应用中的使用寿命，了解其热氧化和辐射氧化降解机制非常重要。我们在此聚焦于聚乙烯这种典型的脂肪族聚合物。描述材料中链缺陷和自由基物种浓度随时间演变的动力学模型确定了瞬态氢过氧化物物种形成及随后分解的一个相关步骤，最终导致羰基缺陷，特别是酮类。在本文中，我们首先总结文献中提出的关于氢过氧化物形成和分解的最相关机理路径，其次，使用基于密度泛函理论（DFT）的第一性原理计算重新审视这些路径。我们的结果部分证实了普遍接受的反应能量，但也提出了替代的、更有利的反应路径。我们强调了环境（是否为结晶态）对一些所研究化学反应结果的影响。我们计算的一个显著结果是羟基自由基在氢过氧化物的分解中起重要作用。基于我们的发现，应该有可能改进当前聚乙烯辐射氧化动力学模拟中使用的方程组和参数。
