Influence of Backbone and Axial Substituent of Catalyst on α-Imino-ketone Nickel Mediated Ethylene (Co)Polymerization

The α-imino-ketone nickel catalyst is an emerging versatile platform that is easy to prepare and allows for the production of branched high molecular weight functionalized polyethylenes. However, study on this catalyst system is rare thus far. In this contribution, by introducing different backbones, flexible and rigid axial substituents into the α-imino-ketone framework, a family of cationic nickel catalysts were synthesized and fully characterized. Without the addition of any activator, systematic studies on ethylene polymerization and copolymerization with polar monomers were performed to explore the influence of both backbone and axial substituent on catalytic activity, polymer molecular weight, branching density and incorporation. In particular, owing to the unique semi-opening feature of the α-imino-ketone framework, the preferred nickel catalyst exhibited high activity of 175 kg·mol−1·h−1 to produce functionalized polyethylene with molecular weight of 13.4 kg·mol−1 and comonomer incorporation of 2.9 mol%.