Rational design of nickel catalysts containing N-acylated imidazolin-2-imine ligand for ethylene copolymerization with polar monomer

Abstract

By taking advantage of electronic influence of ligand design, the novel neutral nickel complexes bearing strong electron-donating N-acylated imidazolin-2-imine ligand were synthesized and characterized. The nickel catalysts conducted ethylene polymerization with high activity and good thermal stability, affording semicrystalline polyethylene with short chain branches (32–46/1000 C atoms). The complex Ni2 bearing adamantyl substituent on the imidazoline ligand showed higher activity than phenyl substituted complex Ni1, and highest activity was observed at 60 °C (up to ~106 g⋅mol−1⋅h−1). Most importantly, the catalysts were also effective for the copolymerization of ethylene and 5-hexenyl acetate with moderate activity (~105 g⋅mol−1⋅h−1). The microstructure analyses by the 13C NMR spectroscopy indicated that the 5-hexenyl acetate was successfully incorporated into the polyethylene main chain with reasonable comonomer content.