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

Abstract

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).

From tetramerization to oligomerization/polymerization of ethylene by dinuclear pyridyl‐imine Co‐ and Ni‐based catalysts

“…[4][5][6] On the other way, there are many reports on late transition metal (LTM) complexes as an interesting class of catalysts due to feasibly preparation and modification, capability of production of a wide range of polyethylene/oligoethylene, intriguing and unusual behavior (e.g., chain-walking olefin polymerization). 1,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Multinuclear LTM catalysts along with their mononuclear analogs are widely used for preparation of ethylene homopolymers/copolymers and oligomers. [22][23][24] In the most cases, not only higher catalytic activity has been observed but also metal-metal cooperative effect in terms of greater selectivity in products has been reported.…”

“…These structures are massively various and belonged to different generation of catalyst systems 4–6 . On the other way, there are many reports on late transition metal (LTM) complexes as an interesting class of catalysts due to feasibly preparation and modification, capability of production of a wide range of polyethylene/oligoethylene, intriguing and unusual behavior (e.g., chain‐walking olefin polymerization) 1,7–21 …”