Zhang Yuxing, Kang Xiaohui, Jian Zhongbao
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, China.
University of Science and Technology of China, Hefei, 230026, China.
Nat Commun. 2022 Feb 7;13(1):725. doi: 10.1038/s41467-022-28282-z.
Polyolefins with branches produced by ethylene alone via chain walking are highly desired in industry. Selective branch formation from uncontrolled chain walking is a long-standing challenge to generate exclusively branched polyolefins, however. Here we report such desirable microstructures in ethylene polymerization by using sterically constrained α-diimine nickel(II)/palladium(II) catalysts at 30 °C-90 °C that fall into industrial conditions. Branched polyethylenes with exclusive branch pattern of methyl branches (99%) and notably selective branch distribution of 1,4-Me unit (86%) can be generated. The ultrahigh degree of branching (>200 Me/1000 C) enables the well-defined product to mimic ethylene-propylene copolymers. More interestingly, branch distribution is predictable and computable by using a simple statistical model of p(1-p) (p: the probability of branch formation). Mechanistic insights into the branch formation including branch pattern and branch distribution by an in-depth density functional theory (DFT) calculation are elucidated.
仅通过链行走由乙烯生成带有支链的聚烯烃在工业上具有很高的需求。然而，从不受控制的链行走中选择性地形成支链是生成纯支化聚烯烃的一个长期挑战。在此，我们报道了在30°C至90°C的工业条件下，使用空间位阻α-二亚胺镍（II）/钯（II）催化剂进行乙烯聚合时所获得的这种理想微观结构。可以生成具有甲基支链（99%）的独特支链模式且1,4-甲基单元的支链分布显著具有选择性（86%）的支化聚乙烯。超高的支化度（>200个甲基/1000个碳）使该明确界定的产物能够模拟乙烯-丙烯共聚物。更有趣的是，可以通过使用简单的p(1 - p)统计模型（p：支链形成的概率）来预测和计算支链分布。通过深入的密度泛函理论（DFT）计算阐明了对支链形成（包括支链模式和支链分布）的机理见解。
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