Rigid Postmetallocene Catalysts for Propylene Polymerization: Ligand Design Prevents the Temperature-Dependent Loss of Stereo- and Regioselectivities
Georgy P. Goryunov, Mikhail I. Sharikov, Andrei N. Iashin, Jo Ann M. Canich, Sarah J. Mattler, J.R. Hagadorn, Dmitry V. Uborsky, Alexander Z. Voskoboynikov
Abstract
Energy- and cost-efficient production of polyolefins in solution processes is achieved, inter alia, by conducting polymerizations at high temperatures. Such processes using single-site catalysts (SSCs) based on group 4 complexes are widely used for the production of ethylene copolymers [e.g., linear low-density polyethylene (LLDPE)], but their implementation in the isotactic polypropylene (iPP) segment remains hampered by the challenge of producing high-melting iPP at high temperatures. Known SSCs (mostly metallocenes), when used to produce iPP, suffer from a rapid decline in performance when the process temperature is increased; just a few are reported to produce high-melting iPP at >100 °C. Herein, we report a family of highly active group 4 postmetallocene catalysts featuring a tridentate pyridine-2,6-bis(phenylenephenolate) ligand framework, the rigidity of which results in minimal temperature-dependent losses in the selectivity of propylene insertions and in the melting points of iPP produced at 70 and 100 °C (up to 160.6 and 160.5 °C, respectively).