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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Modeling Spin-Forbidden Monomer Self-Initiation Reactions in Spontaneous Free-Radical Polymerization of Acrylates and Methacrylates
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Modeling Spin-Forbidden Monomer Self-Initiation Reactions in Spontaneous Free-Radical Polymerization of Acrylates and Methacrylates

机译：模拟丙烯酸酯和甲基丙烯酸酯的自发自由基聚合中的自旋禁止单体自引发反应

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摘要

A spin-forbidden reaction is a reaction in which the total electronic spin-state changes. The standard transition-state theory that assumes a reaction occurs on a single potential energy surface with spinconservation cannot be applied to a spin-forbidden reaction directly. In this work, we derive the crossing coefficient based on the Wentzel-Kramers-Brillouin (WKB) theory to quantify the effect of intersystem crossing on the kinetics of spin-forbidden reactions. Acrylates and methacrylates, by themselves, can generate free radicals that initiate polymerization at temperatures above 120 °C. Previous studies suggest that a triplet diradical is a key intermediate in the self-initiation. The formation of a triplet diradical from two closed-shell monomer molecules is a spin-forbidden reaction. This study provides a quantitative analysis of singlet-triplet spin crossover of diradical species in self-initiation of acrylates and methacrylates, taking into account the effect of intersystem crossing. The concept of crossing control is introduced and demonstrated computationally to be a new likely route to generate monoradicals via monomer self-initiation in high temperature polymerization.
机译：禁止自旋反应是总电子自旋态发生变化的反应。假设反应发生在具有自旋保守性的单个势能表面上的标准过渡态理论不能直接应用于自旋禁止反应。在这项工作中，我们基于Wentzel-Kramers-Brillouin（WKB）理论得出交叉系数，以量化系统间交叉对自旋禁止反应动力学的影响。丙烯酸酯和甲基丙烯酸酯本身可以产生自由基，这些自由基在高于120°C的温度下引发聚合。先前的研究表明，三重双自由基是自我起始的关键中间体。由两个闭壳单体分子形成三重双自由基是自旋禁止反应。这项研究提供了丙烯酸酯和甲基丙烯酸酯自引发双自由基物种单重态-三重态自旋交叉的定量分析，同时考虑了系统间交叉的影响。引入交叉控制的概念，并通过计算证明了它是高温聚合中通过单体自引发生成自由基的一种新的可能途径。

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