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Formation of Octameric Methylaluminoxanes by Hydrolysis of Trimethylaluminum and the Mechanisms of Catalyst Activation in Single‐Site α‐Olefin Polymerization Catalysis
Author(s) -
Hirvi Janne T.,
Bochmann Manfred,
Severn John R.,
Linnolahti Mikko
Publication year - 2014
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201402298
Subject(s) - catalysis , chemistry , polymerization , hydrolysis , alkyl , polymer chemistry , ligand (biochemistry) , olefin fiber , halide , olefin polymerization , photochemistry , stereochemistry , organic chemistry , polymer , biochemistry , receptor
Hydrolysis of trimethylaluminum (TMA) leads to the formation of methylaluminoxanes (MAO) of general formula (MeAlO) n (AlMe 3 ) 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‐catalysts 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 precatalyst or by reaction of the precatalyst with an MAO‐derived AlMe 2 + cation. Thermodynamics suggest that activation through AlMe 2 + transfer is the dominant mechanism because sites that are able to release AlMe 2 + are more abundant than Lewis‐acidic sites. The model catalyst system is demonstrated to polymerize ethene.