π–π interaction effect in insertion polymerization with α-Diimine palladium systems

Abstract

Control of branching densities of polyolefins by polymerization conditions is a great challenge in the field of α-diimine palladium catalyzed olefin (co)polymerization. In this contribution, a series of acenaphthene-based highly sterically hindered α-diimine ligands bearing bulky diarylmethyl moiety and corresponding palladium catalysts have been designed, synthesized, characterized and investigated for ethylene polymerization and copolymerization with several polar monomers. The π-π interaction between the acenaphthene moiety and the phenyl of diarylmethyl moiety was observed. It was suggested that this π-π interaction could freeze the N-aryl-bond rotation at room temperature, resulting in the enhanced axial steric bulk as well as the low branching densities of the polyethylene products. In contrast, at high temperature, the π-π interaction was weaken and resulted in significantly increased branching densities of polyethylene products, indicating branching densities of polyolefins are adjustable within a wide range by polymerization conditions using this catalytic system.