Thermostable polyhalogen-substituted α-diimine nickel precatalysts towards high performance polyethylene elastomer

Abstract

The unsymmetrical bis(imino)acenaphthene derivatives modified by ortho-chloro and para-flouro groups, 1-[2-{(C₆H₅)₂CH}-6-Cl-4-FC₆H₂N]-2-(ArN)C₂C₁₀H₆ (Ar = 2,6-Me₂C₆H₃ L1, 2,6-Et₂C₆H₃ L2, 2,6-ⁱPr₂C₆H₃ L3, 2,4,6-Me₃C₆H₂ L4, 2,6-Et₂-4-MeC₆H₂ L5, 2-{(C₆H₅)₂CH}-6-Cl-4-FC₆H₂ L6), as well as their nickel complexes, LNiBr₂ and LNiCl₂ (Ni1-Ni12), have been synthesized in high yields and fully characterized by the NMR, FT-IR and elemental analysis. Moreover, the molecular structures of Ni1 and Ni11 are confirmed by the single-crystal X-ray diffraction revealing the distorted tetrahedral geometry of Ni1 and the distorted octahedral geometry of Ni11 with dimer configuration. Upon activation with AlEt₂Cl and MMAO, all nickel complexes exhibit high activities in ethylene polymerization up to the range of 10⁷ g of PE (mol of Ni)⁻¹ h⁻¹ at an optimal temperature of 60 °C producing moderately branched polyethylene (31–96 branches / 1000 C) with medium molecular weight (Mw: 0.35–3.06 × 10⁵ g mol⁻¹) and narrow molecular weight distribution (PDI: 1.62 - 2.62). In comparison the polymerization solvent with toluene, hexane, as a potentially industrial application, significantly improve the catalytic performance regarding their activities and molecular weights of resulting polyethylenes. In addition, excellent tensile performance (σ_b up to 25.3 MPa, ε_b up to 1635 %) and good elastic recovery characteristics (up to 69 %) are significant features of the obtained thermoplastic polyethylene elastomer.