Ethylene Polymerization and Copolymerization Using Nickel 2-Iminopyridine-N-oxide Catalysts: Modulation of Polymer Molecular Weights and Molecular-Weight Distributions

Abstract

Molecular weight and molecular-weight distribution are two critical parameters that determine the properties of a polyolefin material. In this contribution, we report the synthesis and characterization of a series of 2-iminopyridine-N-oxide nickel complexes; these catalysts demonstrate very high activities (up to 107 gPE molNi–1 h–1) at very low methylaluminoxane loadings (80 equiv) during ethylene polymerization. By tuning the structures of the catalysts and the polymerization conditions, we show that it is possible to tune the polyethylene molecular weight (Mw: (0.3–301.6) × 104), molecular-weight distribution (polydispersity index (PDI): 1.9–59.7), melting temperature (62.4–132.4 °C), and branching density (9–104/1000 C) over very wide ranges. This translates into the ability to tune the mechanical properties of these polymers as well as their complex viscosities. Equilibria between bis-ligated and mono-ligated nickel species are proposed to play important roles in this system. These nickel catalysts a...