Enhancing Suppression of Chain Transfer via Catalyst Structural Evolution in Ethylene (Co)Polymerization

Usually, the aniline-based late-transition-metal catalysts often require bulky steric substituents on both sides of the ortho-aryl position to achieve efficient suppression of chain transfer in ethylene polymerization. In this contribution, we demonstrated that α-diimine catalysts based on naphthylamine with only one bulky ortho-aryl substituent also demonstrated excellent capabilities to suppress the chain transfer. Firstly, a class of α-diimine nickel and palladium complexes with only one o-aryl-dibenzhydryl or o-aryl-dibenzosuberyl substituent were synthesized and characterized. Secondly, the as-prepared naphthylamine-based nickel catalysts demonstrated outstanding activities and yielded lightly branched (16-40/1000C) polyethylenes with very high molecular weights (445.8-854.3 kg/mol) in ethylene polymerization. In comparison, the corresponding palladium catalysts showed moderate activities, generating moderately branched polyethylenes with moderate molecular weights (21.6-82.0 kg/mol). Moreover, the palladium catalysts could also copolymerize ethylene and methyl acrylate (MA), albeit in low activity (level of 103 g·mol-1·h-1)，providing E-MA copolymers with low to moderate molecular weight (1.4-16.3 kg/mol) and a moderate level of incorporation ratio (2.4-7.4 mol%) and branching density. As compared with aniline-based nickel and palladium catalysts, the naphthylamine-based catalysts displayed a superior ability to suppress the chain transfer reactions and could give access to (co)polymers with orders of magnitude higher molecular weight in ethylene (co)polymerization.