Titanium-based phenoxy-imine catalyst for selective ethylene trimerization: effect of temperature on the activity, selectivity and properties of polymeric side products

• Published in: Catalysis science & technology Vol. 1; no. 6; pp. 162 - 168
• Main Authors: Cordier, Astrid, Breuil, Pierre-Alain, Michel, Typhène, Magna, Lionel, Olivier-Bourbigou, Hélène, Raynaud, Jean, Boisson, Christophe, Monteil, Vincent
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 24.03.2020
• Subjects: Catalysis; Catalysts; Chemical Sciences; High temperature; NMR; Nuclear magnetic resonance; Polyethylenes; Polymerization; Selectivity; Switches; Temperature effects; Titanium
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/c9cy02056j

The reactivity of a phenoxy-imine-ether system (FI)TiCl 3 /MAO was studied toward selective ethylene trimerization. This system was shown to either trimerize or polymerize ethylene depending on the reaction temperature. Its selectivity switches from a significant production of the trimerization product, 1-hexene (85 wt%, 520-450 kg 1-hexene g Ti −1 h −1 ) between 30 and 40 °C, to a moderate polyethylene formation (70-80 wt%, 60-70 kg polyethylene g Ti −1 h −1 ) at a higher reaction temperature ( T > 60 °C). Polymerization was investigated based on an original "polymer-to-catalyst" strategy aiming at identifying the active species responsible for this side reaction. Using DSC, SEC and high temperature 13 C NMR analyses, polyethylenes were found to exhibit high molar masses (>10 5 g mol −1 ) and a low 1-hexene content (<1 mol%) at any temperature. Kinetic studies support that trimerization and polymerization species are generated from the catalyst precursor at 40 °C but a parallel process may occur at a higher temperature. The increase of dispersity to 4.6 at 80 °C suggests a change from single to multi-site catalysis. The poor comonomer incorporation ability of the active species is reminiscent of a molecular Ziegler-Natta or a bulky post-metallocene catalyst. A thermal switch of selectivity for a phenoxy-imine titanium catalyst was studied by combining kinetic studies and a "polymer-to-catalyst" approach.