Effect of halogen and solvent on iron-catalyzed atom transfer radical polymerization
Effect of halogen and solvent on iron-catalyzed atom transfer radical polymerization
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DOI：
10.1039/d1py01601f
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发表时间：
2022-01-21
影响因子：
4.6
通讯作者：
Matyjaszewski, Krzysztof
中科院分区：
文献类型：
--
作者：
Dadashi-Silab, Sajjad;Kim, Khidong;Matyjaszewski, Krzysztof
在原子转移自由基聚合（ATRP）中，卤素原子的有效转移是控制聚合物生长的关键。卤素的性质可影响活化和失活过程期间卤素原子转移的效率。卤素的影响可以与C-X键离解能和卤素/卤化物对过渡金属催化剂的亲和力相关。本文研究了卤离子作为配体存在下，卤素（Br和Cl）和反应介质对铁催化ATRP反应的影响。在基于溴的引发体系中，甲基丙烯酸酯单体的聚合反应得到了良好的控制，而基于氯的引发体系对聚合反应的控制有限。Cl原子对铁催化剂的高亲和力使得其对于生长链的快速失活效率较低，导致聚合物的分子量高于由Δ [M]/[RX]（o）预定的分子量并且具有高分散性。相反，Br可以以更高的效率交换，因此提供了对聚合的良好控制。降低反应介质的极性改善了聚合控制。使用ppm水平的铁催化剂在乙腈（极性更强的溶剂）中的聚合产生具有更大分散度值的聚合物，这是由于与极性较弱的溶剂苯甲醚相反，失活速率较慢，这提供了具有分散度的良好控制的聚合物。
Efficient transfer of halogen atoms is essential for controlling the growth of polymers in atom transfer radical polymerization (ATRP). The nature of halogens may influence the efficiency of the halogen atom transfer during the activation and deactivation processes. The effect of halogens can be associated with the C-X bond dissociation energy and the affinity of the halogens/halides to the transition metal catalyst. In this paper, we study the effect of halogens (Br vs. Cl) and reaction media in iron-catalyzed ATRP in the presence of halide anions as ligands. In Br-based initiating systems, polymerization of methacrylate monomers was well-controlled whereas Cl-based initiating systems provided limited control over the polymerization. The high affinity of the Cl atom to the iron catalyst renders it less efficient for fast deactivation of growing chains, resulting in polymers with molecular weights higher than predetermined by Delta[M]/[RX](o) and with high dispersities. Conversely, Br can be exchanged with higher efficiency and hence provided good control over polymerization. Decreasing the polarity of the reaction medium improved the polymerization control. Polymerizations using ppm levels of the iron catalyst in acetonitrile (a more polar solvent) yielded polymers with larger dispersity values due to the slow rate of deactivation as opposed to the less polar solvent anisole, which afforded well-controlled polymers with dispersity