Chain-Walking Polymerization of α-Olefins by α-Diimine Ni(II) Complexes: Effect of Reducing the Steric Hindrance of Ortho- and Para-Aryl Substituents on the Catalytic Behavior, Monomer Enchainment, and Polymer Properties

Abstract

With Brookhart type α-diimine Ni(II) based catalysts, it is highly challenging to tune polymers branching level and branch-type distribution, which in turn strongly affects thermal and mechanical properties, through the aryl ortho-positions modification, while maintaining high turnover frequencies (TOFs). Herein, we are interested in performing a systematic investigation on the polymerization of 1-octene, 1-decene, and 1-octadecene catalyzed by a series of α-diimine nickel(II) complexes with methyl ligand backbone and different substituents in aryl positions (Ni1–Ni6). In addition to bulky isopropyl and tert-butyl substituents described in the original Brookhart’s work, complexes with different aryl ortho- and para-substituted α-diimine ligands, including the less sterically demanding methyl and ethyl substituents, are investigated. The 13C NMR spectra of the polymers have been assigned in detail, and some unique features have been identified and related to the chain-walking coordination/insertion mechani...