Synthesis of Methyl-Branched Functionalized Polyethylene Using α‑Imino Ketone Nickel Catalysts for High-Temperature Ethylene (Co)Polymerization

The development of high-performance nickel catalysts, which exhibit high thermal stability and facilitate the mediation of high-temperature ethylene (co)­polymerization with polar monomers, remains a significant challenge in the field of olefin polymerization. In this contribution, a series of cationic α-imino ketone single-component nickel catalysts with N-substituents were synthesized and characterized for their sterically open nature. These thermostable nickel catalysts demonstrated high catalytic activity (107 g mol–1 h–1) in ethylene polymerization at temperatures as high as 150 °C. Moreover, they enabled the synthesis of semicrystalline UHMWPE with high molecular weights (up to 153.7 × 104 g mol–1) and melting points up to 128.3 °C. It is particularly interesting that the high-temperature ethylene polymerization process selectively favors the formation of methyl branches, which are derived exclusively from ethylene and hold potential for commercial applications. Most importantly, successful large-scale polymerization experiment on the synthesis of high molecular weight polyethylene in n-heptane using Ni4 at 150 °C, the relative activity is further increased to up to 1.45 × 107 g mol–1 h–1, maintaining high catalytic activity indicate their potential practical applications. These catalysts also demonstrated remarkable competence in ethylene copolymerization with various polar monomers (including methyl 10-undecenoate, vinyltrimethoxysilane, methyl 5-norbornene-2-carboxylate, and acrylates) to produce methyl-branched high-molecular-weight copolymers with high comonomer incorporation levels (up to 19.4 mol %), demonstrating promising potential in polyolefin functionalization. Notably, the resultant high-molecular-weight copolymers exhibited favorable mechanical properties, thereby expanding their application prospects.