Unifying Molecular Weights of Highly Linear Polyethylene Waxes through Unsymmetrical 2,4-Bis(imino)pyridylchromium Chlorides

• Published in: Molecules (Basel, Switzerland) Vol. 25; no. 23; p. 5584
• Main Authors: Gansukh, Badral, Zhang, Qiuyue, Bariashir, Chantsalnyam, Vignesh, Arumugam, Ma, Yanping, Liang, Tongling, Sun, Wen-Hua
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 27.11.2020; MDPI
• Subjects: Chloride; Chlorides - chemistry; Chromium - chemistry; ethylene polymerization; Geometry; highly linear PE waxes; Ligands; Molecular Weight; Nitrogen; NMR; Nuclear magnetic resonance; Organometallic Compounds - chemistry; ortho-fluorinated chromium pre-catalysts; Polyethylene; Polyethylenes - chemistry; Polymerization; Polymers; Polymers - chemistry; Pyridines - chemistry; single-site catalysis; Waxes - chemistry; single-site catalysis; ethylene polymerization; ortho-fluorinated chromium pre-catalysts; highly linear PE waxes
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules25235584

By dealing CrCl3∙3THF with the corresponding ligands (L1–L5), an array of fluoro-substituted chromium (III) chlorides (Cr1–Cr5) bearing 2-[1-(2,4-dibenzhydryl-6-fluoro- phenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridine (aryl = 2,6-Me2Ph Cr1, 2,6-Et2Ph Cr2, 2,6-iPr2Ph Cr3, 2,4,6-Me3Ph Cr4, 2,6-Et2-4-MePh Cr5) was synthesized in good yield and validated via Fourier Transform Infrared (FT-IR) spectroscopy and elemental analysis. Besides the routine characterizations, the single-crystal X-ray diffraction study revealed the solid-state structures of complexes Cr2 and Cr4 as the distorted-octahedral geometry around the chromium center. Activated by either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all the chromium catalysts exhibited high activities toward ethylene polymerization with the MMAO-promoted polymerizations far more productive than with MAO (20.14 × 106 g (PE) mol−1 (Cr) h−1 vs. 10.03 × 106 g (PE) mol−1 (Cr) h−1). In both cases, the resultant polyethylenes were found as highly linear polyethylene waxes with low molecular weights around 1–2 kg mol−1 and narrow molecular weight distribution (MWD range: 1.68–2.25). In general, both the catalytic performance of the ortho-fluorinated chromium complexes and polymer properties have been the subject of a detailed investigation and proved to be highly dependent on the polymerization reaction parameters (including cocatalyst type and amount, reaction temperature, ethylene pressure and run time).