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 thatα-diimine catalysts based on naphthylamine with only one bulky ortho-aryl substituent also demonstrated excellent capabilities to suppress the chain transfer.Firstly,a class ofα-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 13.02×106 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 104-105 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 103 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.