Ab Initio Quantitative Prediction of Tacticity in Radical Polymerization of Poly(methyl methacrylate) by a Molecular Simulation Technique with the Conformation Indexing for Multiple Transition States
Ab Initio Quantitative Prediction of Tacticity in Radical Polymerization of Poly(methyl methacrylate) by a Molecular Simulation Technique with the Conformation Indexing for Multiple Transition States
复制标题
利用多过渡态构象指数分子模拟技术从头定量预测聚甲基丙烯酸甲酯自由基聚合过程中的立构规整度
DOI：
10.1021/acs.jpcc.0c01812
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Nagaoka Masataka
中科院分区：
文献类型：
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作者：
Zizhen Rao;Takayanagi Masayoshi;Nagaoka Masataka
自由基聚合由于其多功能性和生产率而成为生成乙烯基聚合物的关键途径，而立体定向增长的实现一直被认为是非常困难和苛刻的。因此，迫切需要对自由基聚合中获得立构规整度的机理进行具体的研究。实验表明，自由基本体聚合制备的聚甲基丙烯酸甲酯的立构规整度具有间同立构和温度依赖性。在这项研究中，我们打算通过密度泛函理论计算和混合蒙特卡罗/分子动力学模拟[红月亮方法]在微观尺度上合理化这些行为。我们设计了一个独特的构象索引的基础上的多维构象分析，并获得了多达576个过渡态构象的增长反应。576种构象的Boltzmann因子表明，前消旋构象的整体稳定性高于前内消旋构象，此外，低温下的间同立构趋势更大。利用这些构象的能垒，我们成功地模拟了增长反应过程，并实现了定量的一致性的产物的立构规整度的红月亮模拟。这些结果表明，我们的从头算分子模拟程序与构象索引的有效性，实现定量分析的选择性反应。
Free-radical polymerization is a critical route for generating vinyl polymers owing to its versatility and productivity, while the realization of stereospecific propagation has been considered very difficult and demanding. Therefore, a concrete investigation on the mechanism of tacticity obtained in radical polymerization is urgent. Experimentally, tacticity of poly(methyl methacrylate) produced by radical polymerization in bulk was reported to be syndiotactic and temperature-dependent. In this study, we intended to rationalize those behaviors on the microscopic scale via density functional theory calculations and a hybrid Monte Carlo/molecular dynamics simulation [Red Moon methodology]. We devised a unique conformation indexing based on the multidimensional conformational analysis and obtained as many as 576 transition state conformations for the propagation reaction. Boltzmann factors of the 576 conformations implied the overall higher stability of pro-racemo conformations than pro-meso ones and, in addition, the more syndiotactic tendency at low temperature. By the Red Moon simulations utilizing the energy barriers of those conformations, we successfully simulated the propagation reaction process and achieved quantitative agreement of the product tacticity. These results exhibit the validity of our ab initio molecular simulation procedure with the conformation indexing to realize quantitative analysis of the selectivity of reactions.