Li Xiaoxu, Hu Zexu, Mahmood Qaiser, Wang Yizhou, Sohail Sunny, Zou Song, Liang Tongling, Sun Wen-Hua
Chemistry and Chemical Engineering Guangdong Laboratory, Shantou, 515031, China.
Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China.
Dalton Trans. 2024 Nov 19;53(45):18193-18206. doi: 10.1039/d4dt02543a.
In α-diimine nickel catalyst-mediated ethylene polymerization, adjusting catalytic parameters such as steric and electronic factors, as well as spectator ligands, offers an intriguing approach for tailoring the thermal and physical properties of the resulting products. This study explores two sets of -symmetric α-diimine nickel complexes-nickel bromide and nickel chloride-where -steric and electronic substituents, as well as nickel halide, were varied to regulate simultaneously chain walking, chain transfer, and the properties of the polymers produced. These complexes were activated with EtAlCl, resulting in exceptionally high catalytic activities (in the level of 10-10 g (PE) mol (Ni) h) under all reaction conditions. Nickel bromide complexes, with higher -steric hindrance, exhibited superior catalytic activity compared to their less hindered counterparts, whereas the reverse was observed for complexes containing chloride. Increased steric hindrance in both sets of complexes facilitated higher polymer molecular weights and promoted chain walking reactions at lower reaction temperature (40 °C), while the effect became less pronounced at higher temperature (100 °C). However, the electron-withdrawing effect of -substituents hindered the rate of monomer insertion, chain propagation, and chain walking reactions, leading to the synthesis of semi-crystalline polyethylene with an exceptionally high melt temperature of 134.6 °C and a high crystallinity of up to 31.9%. Most importantly, nickel bromide complexes demonstrated significantly higher activity compared to their chloride counterparts, while the latter yielded polymers with higher molecular weights and increased melt temperatures. These high molecular weights, coupled with controlled branching degrees, resulted in polyethylenes with excellent tensile strength (up to 13.9 MPa) and excellent elastic properties (up to 81%), making them suitable for a broad range of applications.
在α-二亚胺镍催化剂介导的乙烯聚合反应中，调节诸如空间位阻和电子因素以及旁观配体等催化参数，为定制所得产物的热性能和物理性能提供了一种引人入胜的方法。本研究探索了两组对称的α-二亚胺镍配合物——溴化镍和氯化镍——其中空间位阻和电子取代基以及卤化镍各不相同，以同时调节链行走、链转移以及所制备聚合物的性能。这些配合物用EtAlCl活化，在所有反应条件下均产生了极高的催化活性（达到10⁶ - 10⁷ g (PE) mol⁻¹ (Ni)⁻¹ h⁻¹）。具有较高空间位阻的溴化镍配合物与其位阻较小的对应物相比，表现出更高的催化活性，而含氯配合物则观察到相反的情况。两组配合物中空间位阻的增加有利于获得更高的聚合物分子量，并在较低反应温度（40 °C）下促进链行走反应，而在较高温度（100 °C）下这种效果变得不那么明显。然而，取代基的吸电子效应阻碍了单体插入、链增长和链行走反应的速率，导致合成出具有高达134.6 °C的异常高熔点温度和高达31.9%的高结晶度的半结晶聚乙烯。最重要的是，溴化镍配合物表现出比其氯化物对应物显著更高的活性，而后者产生的聚合物具有更高的分子量和升高的熔点温度。这些高分子量，再加上可控的支化度，使得聚乙烯具有优异的拉伸强度（高达13.9 MPa）和优异的弹性性能（高达81%），使其适用于广泛的应用。
