Accurate quantum chemistry is used to explain the origins of isospecificity in radical polymerization of calcium methacrylate hydrate (CaMA). Distonic radical–cation interactions are shown to be crucial in determining the reactivity of different coordination structures. Cation coordination to the terminal and incoming monomer side chains reduces radical‐cation separation, enhancing the reactivity of these modes over the stereocontrolling terminal‐penultimate binding modes. This explains why Lewis acid‐mediated radical polymerization often fails to produce highly isotactic polymer for common monomers such as methyl methacrylate. However, theoretical calculations suggest that the poly(CaMA) terminus forms a chelated bridging scaffold in N,N‐dimethylformamide (DMF), which involves the terminal, penultimate and incoming monomer carboxylate groups. This scaffold simultaneously activates the incoming monomer toward propagation and regulates the relative orientation of the terminal and penultimate side chains. The bridging scaffold is disrupted in more polar solvents and/or if alternative nonchelating counter‐cations are employed, leading to loss of isotactic control. These results suggest that higher levels of isotactic control may be achievable if reaction conditions are optimized to favor bridging scaffold formation. The broader importance of these findings to stereocontrol in radical polymerization is also discussed. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019

中文翻译：

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甲基丙烯酸钙自由基聚合中的全同规整：多重螯合是立体控制的关键吗？

准确的量子化学用于解释甲基丙烯酸钙水合物（CaMA）自由基聚合反应中同种特异性的起源。在确定不同配位结构的反应性时，显示出剧烈的自由基-阳离子相互作用是至关重要的。阳离子与末端和进入的单体侧链的配位减少了自由基阳离子的分离，与立体控制的末端倒数第二的结合模式相比，增强了这些模式的反应性。这就解释了为什么路易斯酸介导的自由基聚合反应通常不能产生用于诸如甲基丙烯酸甲酯之类的常见单体的高度全同立构的聚合物。然而，理论计算表明，poly（CaMA）末端在N，N中形成螯合的架桥骨架-二甲基甲酰胺（DMF），涉及末端，倒数第二个和传入的单体羧酸盐基团。该支架同时激活进入的单体以使其传播并调节末端和倒数第二个侧链的相对取向。在更多极性溶剂中和/或如果使用其他非螯合反阳离子会打断架桥支架，从而导致全同立构规整控制的丧失。这些结果表明，如果优化反应条件以利于架桥支架的形成，则可以实现更高水平的全同立构控制。还讨论了这些发现对自由基聚合中立体控制的更广泛的重要性。分级为4 +©2019 Wiley Periodicals，Inc.J.Polym。科学，A部分：Polym。化学 2019年