Producing highly linear polyethylenes by using t-butyl-functionalized 2,6-bis(imino)pyridylchromium(III) chlorides

A new family of t-butyl substituted chromium(III) chloride complexes (Cr1-Cr6), bearing 2-(1-(2,6-dibenzhydryl-4-t-butylphenylimino)ethyl)-6-(1-(arylimino)ethyl)pyridine (aryl = 2,6-Me2C6H3 Cr1, 2,6-Et2C6H3 Cr2, 2,6-i-Pr2C6H3 Cr3, 2,4,6-Me3C6H2 Cr4 and 2,6-Et2-4-MeC6H2 Cr5) or 2,6-bis(1-(2,6-dibenzhydryl-4-t-butylphenylimino)ethyl)pyridine (Cr6), has been synthesized by the reaction of CrCl3·6H2O in good yield with the corresponding ligands (L1-L6), respectively. The molecular structures of Cr2 and Cr6 were characterized by X-ray diffraction highlighted a distorted octahedral geometry with the coordinated N,N,N ligand and three bonded chlorides around the metal center. On activation with modified methylaluminoxane or triisobutyl aluminum, most of the chromium precatalysts exhibit good activities toward ethylene polymerization and produce linear polyethylenes with high-molecular weight. In addition, an in-depth catalytic evaluation of Cr2 was conducted to investigate how cocatalyst type and amount, reaction temperature, and run time affect the catalytic activities and polymer properties.