Effect of Interactions Between the Ligand Distal Group and Cocatalyst in Nickel(II)‐Catalyzed Ethylene Polymerization

The effects of ligand distal substituents on nickel(II)‐catalyzed ethylene polymerization were investigated using bulky α‐diimine Ni(II) catalysts ( Ni1–Ni4 ). para ‐Methoxy‐substituted catalysts ( Ni2–Ni3 ) produced polyethylene with broadened molecular weight distributions and higher melting temperatures (64°C–109°C) compared to unsubstituted analogues, suggesting potential interactions between the methoxy groups and the cocatalyst. However, the steric influence of adjacent methyl groups in Ni2 may partially suppress these interactions, as evidenced by its higher branching density. Replacing methyl backbones with acenaphthyl ( Ni4 ) reduced steric inhibition, leading to improved catalytic activity and thermal stability. Temperature‐dependent studies demonstrated that distal substituents enhance the thermal stability of these diarylmethyl‐based Ni(II) catalyst's activity. A proposed mechanism involving Al–O (alkyaluminium‐methoxy group) interactions suggests that para‐methoxy groups increase axial steric hindrance, slowing chain propagation and broadening molecular weight distribution.