Branched polyethylenes attainable using thermally enhanced bis(imino)acenaphthene-nickel catalysts: Exploring the effects of temperature and pressure

Abstract

The 4,4′-difluorobenzhydryl-containing nickel(II) bromide and chloride chelates, [1-[2,6-{(4-F-C6H4)2CH}2-4-{C(CH3)3}-C6H2N]-2-(ArN)C2C10H6]NiX2 (X = Br: Ar = 2,6-Me2C6H3 Ni1, 2,6-Et2C6H3 Ni2, 2,6-i-Pr2C6H3 Ni3, 2,4,6-Me3C6H2 Ni4, 2,6-Et2-4-MeC6H2 Ni5 and X = Cl: Ar = 2,6-Me2C6H3 Ni6, 2,6-Et2C6H3 Ni7, 2,6-i-Pr2C6H3 Ni8, 2,4,6-Me3C6H2 Ni9, 2,6-Et2-4-MeC6H2 Ni10), have been prepared and fully characterized. The solid-state structures of representative Ni3 and Ni7 display distorted tetrahedral geometries which are maintained in solution with broad paramagnetically shifted resonances a feature of all the 1H and 19F NMR spectra; the effect the halide (Br/Cl) ligand has on the proton and fluorine chemical shifts presents a further point of interest. All ten nickel complexes displayed, on activation with either MAO (methylaluminoxane) or EASC (ethyl aluminum sesquichloride), very high activities (up to 1.36 × 107 g PE mol−1 (Ni) h−1) for ethylene polymerization at either 1 or 10 atm C2H4 with the structural features of the N,N’-ligand influential. Significantly, with EASC as co-catalyst, Ni5 was capable of operating effectively at 90 °C without comprising too much catalytic activity [ca. 4.34 × 106 g PE mol−1 (Ni) h−1]. All the polyethylenes are highly branched with the branching content and type of branch strongly affected by a combination of temperature, pressure and the class of co-catalyst employed. Moreover, good tensile strength (εb up to 2839.5%) and elastic recovery (up to 74%) have been displayed, properties that are characteristic of thermoplastic elastomers (TPEs)