The ability to control catalytic activity and selectivity via in situ changes in catalyst oxidation-state represents an intriguing tool for enhanced polymerization control. Herein, we report foundational evidence that catalysts bearing redox-active moieties may be used to synthesize high molecular weight polyethylene with tailored microstructure. The ability to modulate branching density and identity is facilitated by ligand-based redox chemistry, and is realized via the addition of chemical reductants into the polymerization reactor. Detailed GPC and NMR analyses demonstrate that branching density may be altered by up to ∼ 30% as a function of in situ added reductant.

The utility of photoredox chemistry is expanded to include microstructural control of polyolefins.

Sterically demanding Fe-and Co-based olefin polymerization catalysts 2-Fe and 2-Co bearing 2,6-bis(biphenylmethyl)-4-methylaniline substituted bis(imino)pyridine ligands were synthesized and evaluated for ethylene polymerization. The late-transition metal complexes were characterized by Xray diffraction, NMR spectroscopy, and HRMS, while their resultant polymers were characterized by size-exclusion chromatography and 1 H NMR spectroscopy. While catalyst 2-Fe was inactive, catalyst 2-Co was found to polymerize ethylene and avoid any detectable chain-transfer to aluminum events that are known to plague other Fe-and Co-based catalyst systems and to limit molecular weight. Furthermore, 2-Co displays virtually perfect thermal stability up to 80 8C and shows greatly enhanced thermal stability at 90 8C as compared to previously reported analogues. These observations are attributed to the extreme steric demand imposed by the ligand which mitigates catalyst transfer, deactivation, and decomposition reactions.