Ultra-broad molecular weight distribution polyethylene produced by bis(imino)pyridyl cobalt catalysts

As the largest amount of worldwide produced polymeric materials, the broad applicability requires polyethylene (PE) to possess good processability and mechanical properties through tailored molecular weight (MW) and molecular weight distribution (MWD). Direct synthesis of broad MWD PE with ultra-high molecular weight component is highly desirable and challenging. In this paper, a series of bis(imino)pyridyl cobalt complexes with substituted 8-(p-R-phenyl)naphthylamine (R = OMe, Me, H, CF₃) were designed and synthesized for ethylene polymerization. The intramolecular π-π interactions between the capping aryl groups and the pyridyl ring are clearly observed in bis(imino)pyridyl cobalt complexes, which are a crucial driving force for highly active ethylene polymerization. The existence of syn and anti diastereomers of bis(imino)pyridyl cobalt complexes is also proved by single crystal X-ray diffraction analysis. The ultra-broad MWD PE (MWD >100) with M_w from hundreds to ten million is produced, which is a cooperative result of syn and anti diastereomers of cobalt catalysts and two chain transfer pathways involving β-H transfer to the monomer and chain transfer to aluminum.