Phosphine/Benzocyclone-based Neutral Nickel Catalysts for Ethylene Polymerization and Copolymerization with Polar Monomers

The efficient copolymerization of olefin with polar monomers using nickel-based catalysts presents a longstanding challenge. In this contribution, three phosphine-benzocyclone ligands and corresponding neutral nickel catalysts (Ni1: Ar = Ph; Ni2: Ar = 2-(C6H5)C6H4; Ni3: Ar = 2-[2′,6′-(MeO)2-C6H3]C6H4) were prepared and applied for the ethylene polymerization and copolymerization with polar monomers without any cocatalyst. The bulky substituent groups in complexes Ni2 and Ni3 contributed to high catalytic activities (up to 7.24×106 and 9.04×106 g·molNi−1·h−1, respectively), and produced high-molecular-weight polyethylene (Mw up to 545.7 kDa). Complex Ni3 exhibited high activities for ethylene polymerization at the level of 106 g·molNi−1·h−1 across a wide range from 30 °C to 120 °C, exhibiting excellent high temperature tolerance. These nickel complexes were also effectively employed in the copolymerization of ethylene with methyl acrylate, ethyl acrylate, butyl acrylate and lauryl acrylate, producing copolymers with high molecular weights (Mw up to 80.5 kDa) and high polar monomer incorporation (up to 8.2 mol%). Microstructure analyses revealed that the introduction of large sterically hindered substituents facilitated the incorporation of polar functional units into the polymer backbone. This study demonstrates the potential of these nickel-based catalysts for efficient copolymerization of olefin with polar monomers.