Rigid Postmetallocene Catalysts for Propylene Polymerization: Ligand Design Prevents the Temperature-Dependent Loss of Stereo- and Regioselectivities

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).