title: Improving the performance of methylalumoxane: a facile and efficient method to trap "free" trimethylaluminum.
abstract: The presence of "free" trimethylaluminum (TMA) in methylalumoxane (MAO) solutions can be highly detrimental to the performance of metallocene and "post-metallocene" olefin polymerization catalysts. The most used strategy to remove "free" TMA is to evaporate MAO solutions to dryness, until a free-flowing white powder ("solid MAO") is left. This procedure is tedious and potentially hazardous, because in some cases the distillate is a concentrated hydrocarbon solution of TMA. Moreover, "solid MAO" is poorly soluble in common polymerization media, and once in solution it can regenerate TMA to some extent. This communication reports on a facile alternative, which consists in the controlled addition of a sterically hindered phenol, such as 2,6-di-tert-butylphenol, effectively trapping "free" TMA. We show here that 2,6-di-tert-butylphenol/MAO solutions activate equally well the dichloro-precursors of well-known zirconocene and bis(phenoxyimine)Ti catalysts, and that their use in propene polymerization results in a substantially higher productivity, polymer stereoregularity, and/or average molecular mass compared with activation by MAO alone.
authors.affiliation: Dipartimento di Chimica, Università di Napoli "Federico II", Via Cintia, 80126 Naples, Italy. busico@chemistry.unina.it
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Busico
authors.forename: Roberta
authors.initials: R
authors.lastname: Cipullo
authors.forename: Francesco
authors.initials: F
authors.lastname: Cutillo
authors.forename: Nic
authors.initials: N
authors.lastname: Friederichs
authors.forename: Sara
authors.initials: S
authors.lastname: Ronca
authors.forename: Bing
authors.initials: B
authors.lastname: Wang