Moderately branched ultra-high molecular weight polyethylene by using N,N′-nickel catalysts adorned with sterically hindered dibenzocycloheptyl groups

Five examples of unsymmetrical 1,2-bis (arylimino) acenaphthene (L1 - L5), each containing one N-2,4-bis (dibenzocycloheptyl)-6-methylphenyl group and one sterically and electronically variable N-aryl group, have been used to prepare the N,N '-nickel (II) halide complexes, [1-[2,4-{(C15H13}(2)-6-MeC6H2N]-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-Et-2-4-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-Et-2-4-MeC6H2 Ni10), in high yield. The molecular structures Ni3 and Ni7 highlight the extensive steric protection imparted by the ortho-dibenzocycloheptyl group and the distorted tetrahedral geometry conferred to the nickel center. On activation with either Et2AlCl or MAO, Ni1 - Ni10 exhibited very high activities for ethylene polymerization with the least bulky Ni1 the most active (up to 1.06 x 10(7) g PE mol(-1)(Ni) h(-1) with MAO). Notably, these sterically bulky catalysts have a propensity towards generating very high molecular weight polyethylene with moderate levels of branching and narrow dispersities with the most hindered Ni3 and Ni8 affording ultra-high molecular weight material (up to 1.5 x 10(6) g mol(-1)). Indeed, both the activity and molecular weights of the resulting polyethylene are among the highest to be reported for this class of unsymmetrical 1,2-bis (imino)acenaphthene-nickel catalyst.