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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Computational study of chain transfer to monomer reactions in high-temperature polymerization of Alkyl acrylates
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Computational study of chain transfer to monomer reactions in high-temperature polymerization of Alkyl acrylates

机译：丙烯酸烷基酯高温聚合中链转移至单体反应的计算研究

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This article presents a computational study of chain transfer to monomer (CTM) reactions in self-initiated high-temperature homopolymerization of alkyl acrylates (methyl, ethyl, and n-butyl acrylate). Several mechanisms of CTM are studied. The effects of the length of live polymer chains and the type of monoradical that initiated the live polymer chains on the energy barriers and rate constants of the involved reaction steps are investigated theoretically. All calculations are carried out using density functional theory. Three types of hybrid functionals (B3LYP, X3LYP, and M06-2X) and four basis sets (6-31G(d), 6-31G(d,p), 6-311G(d), and 6-311G(d,p)) are applied to predict the molecular geometries of the reactants, products and transition sates, and energy barriers. Transition state theory is used to estimate rate constants. The results indicate that abstraction of a hydrogen atom (by live polymer chains) from the methyl group in methyl acrylate, the methylene group in ethyl acrylate, and methylene groups in n-butyl acrylate are the most likely mechanisms of CTM. Also, the rate constants of CTM reactions calculated using M06-2X are in good agreement with those estimated from polymer sample measurements using macroscopic mechanistic models. The rate constant values do not change significantly with the length of live polymer chains. Abstraction of a hydrogen atom by a tertiary radical has a higher energy barrier than abstraction by a secondary radical, which agrees with experimental findings. The calculated and experimental NMR spectra of dead polymer chains produced by CTM reactions are comparable. This theoretical/computational study reveals that CTM occurs most likely via hydrogen abstraction by live polymer chains from the methyl group of methyl acrylate and methylene group(s) of ethyl (n-butyl) acrylate.
机译：本文介绍了丙烯酸烷基酯（丙烯酸甲酯，丙烯酸乙酯和丙烯酸正丁酯）自引发的高温均聚过程中链转移至单体（CTM）反应的计算研究。研究了CTM的几种机制。理论上研究了活性聚合物链的长度和引发活性聚合物链的单自由基类型对能垒和相关反应步骤速率常数的影响。所有计算均使用密度泛函理论进行。三种类型的混合功能（B3LYP，X3LYP和M06-2X）和四个基础集（6-31G（d），6-31G（d，p），6-311G（d）和6-311G（d） p））用于预测反应物，产物和过渡态以及能垒的分子几何形状。过渡状态理论用于估计速率常数。结果表明，从丙烯酸甲酯中的甲基，丙烯酸乙酯中的亚甲基和丙烯酸正丁酯中的亚甲基（通过活性聚合物链）中提取氢原子是CTM的最可能机制。同样，使用M06-2X计算的CTM反应速率常数与使用宏观力学模型从聚合物样品测量中估算的速率常数非常吻合。速率常数值不会随着活性聚合物链的长度而发生显着变化。由叔自由基提取氢原子比由仲自由基提取氢具有更高的能垒，这与实验结果一致。通过CTM反应生成的死聚合物链的计算和实验NMR光谱具有可比性。这项理论/计算研究表明，CTM最有可能通过活性聚合物链中的氢从丙烯酸甲酯的甲基和丙烯酸正丁酯的亚甲基中夺取氢而发生。

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