Ultra-high molecular weight elastomeric polyethylene using an electronically and sterically enhanced nickel catalyst

A collection of ten related 1,2-bis(imino) acenaphthene-nickel(II) halide complexes, [1-[2,6-{(C6H5)(2)CH}(2)-4-{C(CH3)(3)}-C6H2N]-2-(ArN)C2C10H6]NiX2 (X = Br: Ar = 2,6-Me2C6H3 Ni1, 2,6-Et2C6H3 Ni2, 2,6-(Pr2C6H3)-Pr-i Ni3, 2,4,6-Me3C6H2 Ni4, 2,6-Et-2-4-MeC6H2 Ni5) and (X = Cl: Ar = 2,6-Me2C6H3 Ni6, 2,6-Et2C6H3 Ni7, 2,6-(Pr2C6H3)-Pr-i Ni8, 2,4,6-Me3C6H2 Ni9, 2,6-Et-2-4-MeC6H2 Ni10), each bearing one sterically and electronically enhanced N-2,6-dibenzhydryl-4-t-butylphenyl group, have been prepared and fully characterized. The unsymmetrical nature of the chelating bis(imino) acenaphthene is confirmed in the paramagnetic H-1 NMR spectra for Ni1-Ni10, while the molecular structures of Ni1, Ni2 and Ni6 highlight the unequal steric protection of the nickel center imposed by their respective N, N-ligands. On activation with either Et2AlCl or MMAO, all the nickel complexes were highly active catalysts in ethylene polymerization [as high as 1.26 x 10(7) g of PE per mol of Ni per h] affording exceptionally high molecular weight (up to 3.1 x 10(6) g mol(-1)) hyper-branched polyethylene. Analysis of the mechanical properties reveals the ultra-high molecular weight polymers possess high tensile strength, excellent shape fixity and elastic recovery (up to 69%) as well as high elongation at break (epsilon(b) = 843.9%); such materials offer a promising alternative to current thermoplastic elastomers (TPEs).