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

Abstract

Comprehensive Summary 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 (up to 13.02 × 10 6 g·mol –1 ·h –1 ) 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 (level of 10 4 —10 5 g·mol –1 ·h –1 ), generating moderately branched (47—78/1000C) 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 activities (level of 10 3 g·mol –1 ·h –1 ), providing E‐MA copolymers with low to moderate molecular weights (1.4—16.3 kg/mol) and a moderate level of incorporation ratio (2.4—7.4 mol%) and branching density (53—84/1000C). 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.

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