CF3O-Functionalized Bis(arylimino)pyridine-Cobalt Ethylene Polymerization Catalysts: Harnessing Solvent Effects on Performance and Polymer Properties

Enhancing the properties of polymeric materials through the fine control of molecular weight and dispersity provides key objectives to be considered in the design of polymerization catalysts. Herein, solution polymerization of ethylene was studied using bis(arylimino)pyridine-cobaltous chloride precatalysts, [2-[CMeN{2,6-{(C6H5)2CH}2-4-(F3CO)C6H2}]-6-(CMeNAr)C5H3N]CoCl2 [Ar = 2,6-Me2C6H3 (Co1), 2,6-Et2C6H3 (Co2), 2,6-i-Pr2C6H3 (Co3), 2,4,6-Me3C6H2 (Co4), or 2,6-Et2-4-MeC6H2 (Co5)], each incorporating one N-aryl group appended with both o-benzhydryl and p-trifluoromethoxy groups. In the presence of MAO or MMAO, all complexes displayed very high activities [≤11.2 × 106 g (PE) mol-1 (Co) h-1 for Co1/MAO] as ethylene polymerization catalysts generating high-molecular weight polyethylene (≤5.05 × 105 g mol-1) with narrow dispersity (Mw/Mn ≥ 1.76). Notably, higher activity was achieved in hexane than in toluene with the added economic benefit that less aluminoxane activator was required [e.g., 650:1 Al:Co (hexane) vs 1750:1 Al:Co (toluene)]. All polyethylenes were of high linearity as evidenced by 1H and 13C nuclear magnetic resonance spectroscopy and differential scanning calorimetry. In addition to the in-depth polymerization studies, the synthetic details for Co1-Co5 and their precursor bis(arylimino)pyridines are reported along with associated characterization data, including the X-ray structures for Co2 and Co5.