Axial-phenyl Constrained Bis(imino)acenaphthene-Nickel Precatalysts Enhancing Ethylene Polymerization

Abstract

To enhance the performance of the bis(imino)acenaphthene-nickel precatalyst, the axial phenyl group is introduced on the acenaphthenyl backbone forming five analogues, bis(aryl)imino-5-phenylacenaphthene nickel bromides (aryl: 2,6-dimethylphenyl, Ni1; 2,6-diethylphenyl, Ni2; 2,6-diisopropylphenyl, Ni3; 2,4,6-trimethylphenyl, Ni4; 2,6-diethyl-4-methylphenyl, Ni5). The molecular structures of mononuclear Ni2 and dinuclear Ni3 are confirmed as the distorted tetrahedron and square-pyramidal geometry around nickel core, respectively. All title precatalysts achieve better activity as well as thermostability for ethylene polymerization and deliver polyethylene elastomer with higher molecular weight and more branches than the benchmark nickel precatalyst proposed by Brookhart. Specifically, good catalytic activities of Ni2/EASC can maintain 4.52 × 106 g PE mol−1 (Ni) h−1 even at 100 oC. More importantly, the resultant polyethylenes show excellent menchanical properties with high strain (> 1000%) and stress (> 10 MPa) value observed during the tensile stress-strain tests. Illustrated by the result of topographic steric maps, there is sufficient space around nickel center for ethylene to conduct coordination and facilitate the polymeric propagation. The introduction of axial phenyl group into the backbone of nickel complexes not only elevate the catalytic performance but also provide these polyethylene elastomers with attractive properties.