Ligand steric hindrance and electronic effects play a crucial role in late-transition metal-catalyzed olefin polymerization. In this research, a series of o-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 10⁷ g mol⁻¹ h⁻¹. The produced polyethylenes displayed a broad spectrum of molecular weights (12.2–871.7 kg mol⁻¹) 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 o-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%).

中文翻译：

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邻芳基卤素效应对乙烯聚合的影响：空间效应与电子效应

配体空间位阻和电子效应在后过渡金属催化的烯烃聚合中起着至关重要的作用。在这项研究中，合成了一系列带有大二苯甲基取代基的邻芳基卤化α-二亚胺配体及其相应的镍催化剂，并进行了彻底的表征。镍催化剂在乙烯聚合中表现出非常高的活性，达到高达10 ⁷ g mol ^-1 h ^-1的高速率。当使用不同的镍催化剂在固定温度下聚合时，所生产的聚乙烯表现出广泛的分子量（12.2–871.7 kg mol ^-1 ），但保持一致的支化密度（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都有显着影响。较高的温度导致形成具有较低分子量和增加的支化密度的聚乙烯。有趣的是，邻芳基卤素显着影响聚乙烯的分子量。卤素取代基的大小主要决定聚乙烯的分子量。然而，就支化密度而言，这些取代基的空间效应和电子效应似乎相互抵消。此外，由溴和氯取代的镍催化剂生产的支化高分子量聚乙烯是优异的聚乙烯热塑性弹性体，具有高断裂应变值（688-2478%）和高应变恢复值（42-62%）。