Synthesis and characterization of first- and second-generation polyamide pyridylimine nickel dihalide metallodendrimers and their uses as catalysts for ethylene polymerization

Abstract

First- and second-generation pyridylimine-terminated dendrimeric ligands were prepared by the reaction of the corresponding amine-terminated aromatic polyamide dendrimers with 2-acetylpyridine. The pyridylimine terminal groups were used as bidentateN,N ligands of nickel halide to prepare the corresponding first-generation and second-generation nickel dihalidemetallodendrimers C1 and C2, respectively. The synthesized dendrimers and metallodendrimers were characterized by elemental and spectral analyses. C1 and C2 were evaluated as catalyst precursors for ethylene oligomerization after being activated with methylaluminoxane (MAO) and diethylaluminum chloride (Et2AlCl) under 1 atm and 5 atm pressure of ethylene. In both cases, the use of 1 atm or 5 atm pressure of ethylene and a 1500:1 Al:Ni molar ratio for C1 and C2 resulted in high catalytic activities toward ethylene polymerization.Uponactivation withMAOand Et2AlCl, C1 exhibited promising activities toward ethylene polymerization and produced linear chain structures that were associated with high density polyethylene. In contrast, C2 produced a polymer with the branching nature of low density polyethylene under similar conditions.