Formation of octameric methylaluminoxanes by hydrolysis of trimethylaluminum and the mechanisms of catalyst activation in single-site alpha-olefin polymerization catalysis

Hirvi, Janne T., Bochmann, Manfred, Severn, John R. and Linnolahti, Mikko (2014) Formation of octameric methylaluminoxanes by hydrolysis of trimethylaluminum and the mechanisms of catalyst activation in single-site alpha-olefin polymerization catalysis. ChemPhysChem, 15 (13). 2732–2742. ISSN 1439-4235

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Abstract

Hydrolysis of trimethylaluminum (TMA) leads to the formation of methylaluminoxanes (MAO) of general formula (MeAlO)n(AlMe3)m. The thermodynamically favored pathway of MAO formation is followed up to n = 8, showing the major impact of associated TMA on the structural characteristics of the MAOs. The MAOs bind up to five TMA molecules, thereby inducing transition from cages into rings and sheets. Zirconocene catalyst activation studies using model MAO co-cat alysts show the decisive role of the associated TMA in forming the catalytically active sites. Catalyst activation can take place either by Lewis-acidic abstraction of an alkyl or halide ligand from the precata- lyst or by reaction of the precatalyst with an MAO-derived AlMe2+ cation. Thermodynamics suggest that activation through AlMe2+ transfer is the dominant mechanism because sites that are able to release AlMe2+ are more abundant than Lewis-acidic sites. The model catalyst system is demonstrated to polymerise ethene.

Item Type: Article
Faculty \ School: Faculty of Science > School of Chemistry
Depositing User: Pure Connector
Date Deposited: 23 Dec 2015 15:00
Last Modified: 20 Sep 2020 23:47
URI: https://ueaeprints.uea.ac.uk/id/eprint/55884
DOI: 10.1002/cphc.201402298

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