Multimodal Polyethylenes Produced by Hybrid and Unsymmetric α-Diimine Nickel Catalysts: The Roles of Syn/Anti Diastereomers and Imine Metathesis

The broad applicability requires polyethylene (PE) to possess good processability and mechanical properties; direct synthesis of bimodal or multimodal PEs using a well-defined catalyst is therefore of considerable academic and industrial interest. In this paper, a series of dibenzobarrelene-derived α-diimine nickel complexes with a substituted 8-(p-R-phenyl)naphthylamine (R = OMe, Me, CF3) and a naphthylamine were designed and synthesized for ethylene polymerization by unsymmetric and hybrid aniline strategies. At low temperature (<50 °C), bimodal PEs are obtained because of the presence of syn and anti diastereomers of α-diimine nickel catalysts. At high temperatures (>65 °C), multimodal PEs with broad molecular weight distributions are produced, which arises from the cooperative contributions of syn/anti diastereomers of α-diimine nickel catalysts and imine metathesis. The imine metathesis observed for these hybrid α-diimine nickel complexes provides a new mechanistic perspective on their unique ethylene polymerization behavior and a strategy for tailoring PE molecular weight distributions by using well-defined catalysts.