Attaining highly branched polyethylene elastomers by employing modified α-diiminonickel(II) catalysts: Probing the effects of enhancing fluorine atom on the ligand framework towards mechanical properties of polyethylene

Abstract

A novel panel of 1-(2,6-dibenzhydryl-3,4-difluorophenylimino)-2-aryliminoacenaphthylenes was synthesized and reacted with (DME)NiBr2 to give rise to mono and di-nuclear complexes with the general formula of LNiBr2 and L2Ni2Br4, respectively. All the ligands were characterized by elemental analysis, FT-IR, 1H, 13C, 19F NMR spectroscopy, and their complexes were analyzed by elemental analysis and FT-IR spectroscopy. The true coordination nature of the ligands in Ni2 and Ni5 was confirmed through single-crystal XRD studies and thus reveal the distorted square-pyramidal and tetrahedral geometry around the Ni(II) center, respectively. In connection with this, complex Ni2 forms a di-nuclear structure whereas Ni5 formed a mono-nuclear structure in the solid-state. These complexes were tested as catalysts for the polymerization of ethylene in the presence of aluminum reagents like methylaluminoxane (MAO), modified methylaluminoxane (MMAO) or dimethylaluminum chloride (Me2AlCl). The obtained polyethylenes are highly branched and ultra-high molecular weight (Mw = 11.42 × 105 g mol−1, Tm = 82.6 °C) with narrow polydispersity. The mechanical properties of the polyethylenes are analyzed through dynamic mechanical analysis (DMA), monotonic stress-strain test and thus revealed that high tensile strength, good elastomeric recovery (up to 63%) and highest elongation ability (up to 2592.6%) without break are the key highlights of the present work.