Simple and Sterically Open Nickel Catalyst for Ultrahigh Molecular Weight Polyethylene Synthesis

The suppression of chain transfer reactions to produce high-molecular-weight polymers is a long-standing issue in catalytic polymerization, especially in nickel-mediated olefin polymerization. Installing sterically hindered ligands into nickel catalysts has become a general principle for producing high-molecular-weight polyolefins, which are globally important plastics. Herein, we report a new concept for preparing ultrahigh-molecular-weight polyethylene (UHMWPE) using an extremely simple nickel catalyst. Bis(o-iminobenzosemiquinonato)nickel precatalysts derived from sterically open and redox-active noninnocent o-iminobenzoquinone ligands are easily prepared from commercially available compounds, which are air-stable and highly soluble. Activation at 20- or 50-fold of Et2AlCl enables the nickel precatalysts to produce UHMWPEs (Mn up to 4,211 kDa) under ambient conditions. In particular, functionalized UHMWPEs are accessible at only 1 bar. Experimental evidence proposes the formation of a six-coordinate octahedral nickel active species and rules out the classical four-coordinate square-planar nickel active species. Density functional theory calculations further indicate the suppression of chain transfer by this unprecedented nickel platform with sterically open ligands.