Binuclear Nickel Catalysts Enable One-Step Copolymerization of Ethylene with 2-Allylphenol to Phenol-Functionalized Branched Polyethylenes

Abstract

One-step ethylene copolymerization with readily available short-chain alkenyl phenols is an attractive alternative to post-modification or the use of designed phenolic comonomers for preparing phenol-functionalized polyethylenes, yet prior examples have largely relied on early transition-metal catalysts or phosphine-sulfonate Pd systems and typically afford linear backbones. Here we report binuclear Ni-catalyzed ethylene copolymerization with 2-allylphenol enabled by Et2AlCl, which serves as both a cocatalyst and an effective pretreatment reagent for the protic comonomer. Under 1 atm ethylene, phenol-functionalized branched polyethylenes are obtained with activities up to 1200 kg/(mol cat·h·atm), Mn = 19.1-84.1 kg/mol, phenolic incorporation of 0.5-2.7 mol%, and branching densities of 78-99 CH3/1000C. Varying Et2AlCl pretreatment, comonomer concentration and temperature reveals coupled trade-offs between incorporation and productivity/Mn. NMR analysis further reveals both in-chain and chain-end incorporation motifs of the phenolic comonomer.