The synthesis of polyethylenes with concurrent high mechanical and elastic properties at elevated reaction temperatures using nickel catalysts proves to be challenging, primarily due to excessive chain walking and transfer reactions. In this study, hybrid steric hindrance, involving flexible cycloalkyl and relatively compact benzhydryl groups, was introduced into the α-diimine structure to prepare a set of nickel complexes, aiming to enhance the catalytic performance and polyethylene properties simultaneously for ethylene polymerization. Upon activation with EASC, these precatalysts displayed exceptionally high activity (up to 4.3 × 10⁷ g mol⁻¹ h⁻¹ at 30 °C) and high thermal stability (activity up to 1.8 × 10⁶ g mol⁻¹ h⁻¹ at 110 °C over a period of 30 min). High to ultra-high molecular weights and a moderate to high number of branches (34–145 per 1000C) along with narrow unimodal dispersity (PDI ≤ 2) across various reaction conditions are the characteristics of the obtained polyethylene. Of significant note is that the polyethylene obtained at high reaction temperature using these precatalysts exhibited significantly distinguished mechanical and elastic properties. Particularly, the PE prepared at 80 °C displayed high tensile strength (σ = 25.9 MPa) concurrently with high elastic recovery (SR = 70%), a combination of mechanical and elastic properties rarely reported in polyethylenes prepared at high temperatures. These results highlight the role of the hybrid steric bulk strategy in effectively controlling the ratio of chain walking and chain growth reactions.

中文翻译：

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在 α-二亚胺镍预催化剂中使用混合空间方法的高性能聚乙烯弹性体

使用镍催化剂在升高的反应温度下合成同时具有高机械和弹性性能的聚乙烯被证明是具有挑战性的，这主要是由于过度的链行走和转移反应。本研究将柔性环烷基和相对紧凑的二苯甲基的杂化位阻引入α-二亚胺结构中，制备了一组镍配合物，旨在同时增强乙烯聚合的催化性能和聚乙烯性能。用 EASC 活化后，这些预催化剂表现出极高的活性（30 °C 时高达 4.3 × 10 ⁷ g mol ^-1 h ^-1）和高热稳定性（30 °C 时活性高达 1.8 × 10 ⁶ g mol ^-1 h ^-1） 110°C，持续 30 分钟）。所得聚乙烯的特点是具有高至超高分子量、中至高支链数（每 1000C 34-145 个）以及在各种反应条件下的窄单峰分散性 (PDI ≤ 2)。值得注意的是，使用这些预催化剂在高反应温度下获得的聚乙烯表现出显着的机械和弹性性能。特别是，在 80 °C 下制备的 PE 显示出高拉伸强度（σ = 25.9 MPa），同时具有高弹性回复率（SR = 70%），这是高温制备的聚乙烯中很少报道的机械和弹性性能的结合。这些结果凸显了混合空间策略在有效控制链行走和链增长反应比率方面的作用。