Zhang Yuxing, Wang Chaoqun, Mecking Stefan, Jian Zhongbao
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Renmin Street 5625, Changchun, 130022, China.
University of Science and Technology of China, Hefei, 230026, China.
Angew Chem Int Ed Engl. 2020 Aug 17;59(34):14296-14302. doi: 10.1002/anie.202004763. Epub 2020 Jul 6.
Branched polyolefin microstructures resulting from so-called "chain walking" are a fascinating feature of late transition metal catalysts; however, to date it has not been demonstrated how desirable branched polyolefin microstructures can be generated thereby. We demonstrate how highly branched polyethylenes with methyl branches (220 Me/1000 C) exclusively and very high molecular weights (ca. 10 g mol ), reaching the branch density and microstructure of commercial ethylene-propylene elastomers, can be generated from ethylene alone. At the same time, polar groups on the main chain can be generated by in-chain incorporation of methyl acrylate. Key to this strategy is a novel rigid environment in an α-diimine Pd catalyst with a steric constraint that allows for excessive chain walking and branching, but restricts branch formation to methyl branches, hinders chain transfer to afford a living polymerization, and inverts the regioselectivity of acrylate insertion to a 1,2-mode.
由所谓“链行走”产生的支化聚烯烃微观结构是后过渡金属催化剂的一个迷人特性；然而，迄今为止，尚未证明如何由此生成理想的支化聚烯烃微观结构。我们展示了如何仅由乙烯生成具有甲基支链（220个甲基/1000个碳原子）且分子量非常高（约10⁶ g/mol）的高度支化聚乙烯，其支链密度和微观结构达到了商业乙烯 - 丙烯弹性体的水平。同时，通过在主链中引入丙烯酸甲酯可以生成主链上的极性基团。该策略的关键在于α - 二亚胺钯催化剂中一种新型的刚性环境，其具有空间位阻，允许过度的链行走和支化，但将支链形成限制为甲基支链，阻碍链转移以实现活性聚合，并将丙烯酸酯插入的区域选择性反转至1,2 - 模式。
