Studies on Methylaluminoxane Catalyst Activators

The first part of this PhD was devoted to the structural characterization of methylaluminoxane (MAO). Initially the work focused upon MAO formation by studying the hydrolysis reaction of trimethylaluminium (TMA), with a greater interest in the initial reaction steps of TMA with H2O. This was attempted by using 1H VT NMR spectroscopy and by combining infrared spectroscopy with the matrix isolation technique. Low temperature NMR experiments successfully led to the identification of the AlMe3·H2O adduct as the first intermediate, followed by formation of Me2AlOH, when THF was employed as a solvent. \nAnother approach focused on the characterization of MAO by developing a fast and reliable method for quantification of the TMA content of commercial MAO solutions via 1H-NMR spectroscopy with addition of donors. This research also showed that MAO contains a small amount of certain structures, which upon addition of THF or pyridine can lead to the formation of cationic species [AlMe2L2]+. \nThe second part of this work was devoted to the enhancement of MAO’s catalytic efficiency by kinetic studies on 1-hexene. The primary aim was to produce MAO soluble in aliphatic hydrocarbons by addition of branched or long chain aluminium trialkyls, which proved to be effective solubilizing agents, and by modification of MAO with long chain silanols. Addition of silanols led to polymers with lower . Differences in productivity, polymer molecular weight and number of active species were shown to be primarily a linear function of the TMA concentration. \nAn important part of this PhD was the development of a synthetic route towards ethyl-iso-butylaluminoxane (EBAO) and use in 1-hexene polymerization. This is the first study where EBAO is successfully used as a soluble component in 1-hexene polymerization in heptane and leads to comparable or even higher productivities and higher number average molecular weights compared to the MAO catalytic systems.