Improving 1-Hexene Incorporation of Highly Active Cp–Chromium-Based Ethylene Polymerization Catalysts

Abstract

Single-site chromium catalysts for olefin polymerization with donor functionalized cyclopentadienyl (Cp) ligands have been modified in order to improve their incorporation ability for the comonomer 1-hexene into the polymer chain under maintenance of their very high catalytic activities. A trimethylsilyl substituent in combination with a fused thiophene ring at the Cp ligand has been identified as the best ligand so far, leading to a doubling in 1-hexene incorporation and polyethylene (PE) with up to 27% 1-hexene content (by weight) has been obtained. The complexes lead to PE with molecular weight in the range of 50 000 to 800 000 g mol–1 when used in homogeneous solution, however after supporting the complex on silica ultrahigh molecular weight polyethylene (UHMW-PE) is formed with 9.9% of 1-hexene incorporated into the chain. Although other known catalysts incorporate even more 1-hexene, the presented system is different as it combines considerable α-olefin incorporation with very high polymer molecular...