Dai Jianjian, Dai Shengyu
Institutes of Physical Science and Information Technology, Anhui University, Hefei, Anhui, 230601, China.
Anhui Laboratory of Molecule-Based Materials, Key Laboratory of Functional Molecular Solids, Ministry of Education, School of Chemistry and Materials Science, Anhui Normal University, Wuhu 241002, China.
Dalton Trans. 2024 Jun 4;53(22):9286-9293. doi: 10.1039/d4dt00850b.
Ligand steric hindrance and electronic effects play a crucial role in late-transition metal-catalyzed olefin polymerization. In this research, a series of -aryl halogenated α-diimine ligands bearing bulky dibenzhydryl substituents, along with their corresponding nickel catalysts, have been synthesized and thoroughly characterized. The nickel catalysts demonstrated very high activity in ethylene polymerization, achieving a high rate of up to 10 g mol h. The produced polyethylenes displayed a broad spectrum of molecular weights (12.2-871.7 kg mol) but maintained consistent branching densities (50-82/1000 C) when polymerized at a fixed temperature with different nickel catalysts. Notably, the polymerization temperature has a significant influence on both the molecular weight and branching density of the resulting polyethylene. Higher temperatures led to the formation of polyethylenes with lower molecular weights and increased branching densities. Interestingly, the -aryl halogens significantly impact the molecular weight of the polyethylene. The size of the halogen substituents primarily determines the molecular weight of the polyethylene. However, in terms of branching density, the steric and electronic effects of these substituents appear to counteract each other. In addition, the branched high molecular weight polyethylenes from the bromine and chlorine substituted nickel catalysts are excellent polyethylene thermoplastic elastomers with high strain at break values (688-2478%) and high strain recovery values (42-62%).
配体的空间位阻和电子效应在后期过渡金属催化的烯烃聚合反应中起着关键作用。在本研究中，合成了一系列带有庞大二苯甲基取代基的芳基卤代α-二亚胺配体及其相应的镍催化剂，并进行了全面表征。这些镍催化剂在乙烯聚合反应中表现出非常高的活性，高达10 g mol h的高反应速率。所制备的聚乙烯分子量范围宽广（12.2 - 871.7 kg mol），但在使用不同镍催化剂于固定温度下聚合时，支化密度保持一致（50 - 82/1000 C）。值得注意的是，聚合温度对所得聚乙烯的分子量和支化密度均有显著影响。较高温度导致形成分子量较低且支化密度增加的聚乙烯。有趣的是，芳基卤对聚乙烯的分子量有显著影响。卤素取代基的大小主要决定了聚乙烯的分子量。然而，就支化密度而言，这些取代基的空间位阻和电子效应似乎相互抵消。此外，由溴和氯取代的镍催化剂制得的支化高分子量聚乙烯是优异的聚乙烯热塑性弹性体，具有高断裂伸长率值（688 - 2478%）和高应变回复率值（42 - 62%）。
