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

By dealing CrCl(3)∙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-Me(2)Ph Cr1, 2,6-Et(2)Ph Cr2, 2,6-iPr(2)Ph Cr3, 2,4,6-Me(3)Ph Cr4, 2,6-Et(2)-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 × 10(6) g (PE) mol(−1) (Cr) h(−1) vs. 10.03 × 10(6) 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).