Alkylaluminum activator effects on polyethylene branching using a N,N′-nickel precatalyst appended with bulky 4,4′-dimethoxybenzhydryl groups

Ten unsymmetrical N,N'-bis (imino) acenaphthene-nickel (II) halide complexes, [1-[2,6-{(4-MeOC 6 H 4 ) 2 CH} 2 –4-MeC 6 H 2 N]-2-(ArN)C 2 C 10 H 6 ]NiX 2 , each appended with one N-2,6-bis(4,4'-dimethoxybenzhydryl)-4-methylphenyl group, have been synthesized and characterized. The molecular structures of Ni1, Ni3, Ni5 and Ni6 highlight the variation in steric protection afforded by the inequivalent N-aryl groups; a distorted tetrahedral geometry is conferred about each nickel center. On activation with diethylaluminum chloride (Et 2 AlCl) or methylaluminoxane (MAO), all complexes showed high activity at 30°C for the polymerization of ethylene with the least bulky bromide precatalysts (Ni1 and Ni4), generally the most productive, forming polyethylenes with narrow dispersities [M w /M n : < 3.4 (Et 2 AlCl), < 4.1 (MAO)] and various levels of branching. Significantly, this level of branching can be influenced by the type of co-catalyst employed, with Et 2 AlCl having a predilection towards polymers displaying significantly higher branching contents than with MAO [T m : 33.0–82.5°C (Et 2 AlCl) vs. 117.9–119.4°C (MAO)]. On the other hand, the molecular weights of the materials obtained with each co-catalyst were high and, in some cases, entering the ultra-high molecular weight range [M w range: 6.8–12.2 × 10 5 g mol −1 (Et 2 AlCl), 7.2–10.9 × 10 5 g mol −1 (MAO)]. Furthermore, good tensile strength (ε b up to 553.5%) and elastic recovery (up to 84%) have been displayed by selected more branched polymers highlighting their elastomeric properties.