Synthesis of Various Branched Ultra-High-Molecular-Weight Polyethylenes Using Sterically Hindered Acenaphthene-Based α-Diimine Ni(II) Catalysts

A series of highly sterically hindered acenaphthene-based α-diimine nickel complexes with the remote R group in 4-position of diarylmethyl moiety have been synthesized and characterized. Activated with Et2AlCl, ethylene polymerization by these nickel complexes is investigated in detail, involving the remote substituent effect and influence of polymerization temperature on catalyst activity, thermal stability, polymer molecular weight, and branching density. These thermostable nickel catalysts are very active (up to 5.1 × 106 g·mol–1·h–1) for ethylene polymerization and capable of producing various moderate to highly branched (26–71/1000 C) ultra-high-molecular-weight polyethylenes (UHMWPEs, Mw up to 4.5 × 106 g·mol–1). These polymeric materials with such unique structure show properties characteristic of thermoplastic elastomers, i.e., good elastomeric recovery and high strain at break.