Add time:09/09/2019         Source:sciencedirect.com

The properties of polyolefin resins depend very much on their molecular weights, the amount of side chain branchings and molecular weight distributions. One way to obtain such tailored products in only one reaction step consists in the application of dissymmetric multi nuclear catalysts with different active sites. Since every active site is producing its own polymer, a “molecular blending” is the result. In order to reach this goal, a variety of mono, di- and trinuclear complexes of iron, titanium and zirconium, containing 2,6-bis(aryliminoethyl)pyridine and phenoxyimine building blocks have been synthesized and characterized. The reaction of iodo functionalized 2,6-bis(arylimino-ethyl)pyridine derivatives with alkyne functionalized phenoxyimine compounds via Sonogashira cross-coupling reactions results in ligand precursors that can provide coordination sites for two different metals. Trinuclear complexes with the combinations Ti/Fe and Zr/Fe, each molecule containing two iron atoms in two 2,6-bis(aryliminoethyl)pyridine units, gave the best ethylene polymerization results. Due to fast ligand exchange reactions, dinuclear iron/titanium complexes could not be isolated from reactions of mono(phenoxyimine) titanium complexes and the coupled bis(chelate) ligand precursor. Since the metal centers show their best performances at different polymerization temperatures, the compositions (and, therefore, the molecular weight distributions) of the desired polyethylenes may be adjusted by a simple change of the reaction temperature.

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