Bimodal Polyethylenes Synthesized by Flexible Fluorinated “Sandwich” α‐Diimine Nickel( II ) Catalysts

Bimodal polyethylene, a polyolefin material comprising both high and low molecular weight polyethylene fractions, is widely used in practical applications such as high‐performance films and pressure pipes. However, the efficient and controllable synthesis of bimodal polyethylene in a single reactor remains a significant challenge. In this work, a series of flexible fluorinated “sandwich” α‐diimine Ni(II) complexes ( Ni1 – Ni4 ) were rationally designed and synthesized. The introduction of fluorine substituents at various positions on the benzyl group of ligand effectively modulated the catalytic performance, influencing critical polymer properties such as activity, molecular weight, molecular weight distribution, and branching density. Upon activation with Et 2 AlCl, all Ni(II) catalysts exhibited high activities (up to 9.12 × 10 6  g mol −1  h −1 ) and produced polyethylenes with either broad or distinctly bimodal molecular weight distributions. This distinctive behavior is attributed to the dynamic equilibrium between the syn and anti isomers of the catalyst. The content of the high molecular weight fraction depended critically on key polymerization parameters, including temperature, ethylene pressure, and solvent. The resulting bimodal polyethylene products exhibited excellent mechanical properties, with tensile strength ranging from 10.2 to 42.6 MPa. This study on the effect of fluorine substitution pattern in “sandwich” α‐diimine Ni(II) catalysts for the synthesis of bimodal polyethylene offers a novel and streamlined strategy for producing high‐performance polyethylene.