Studies on Methylaluminoxane Catalyst Activators Chrysoula Pateraki
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Studies on Methylaluminoxane Catalyst Activators Chrysoula Pateraki PhD Thesis University of East Anglia School of Chemistry September 2014 © This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the author and that use of any information derived there from must be in accordance with current UK Copyright Law. In addition, any quotation or extract must include full attribution. i Statement of Original Work The work presented in this thesis has been conducted by the author, Chrysoula Pateraki, and is, to the best of her knowledge, original, except where references have been made to other people’s work. The corresponding references have been detailed in each chapter. i Abstract 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 1 reaction steps of TMA with H2O. This was attempted by using H 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. Another 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] . The 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. An 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. ii Table of Contents Statement of Original Work ........................................................................................................ i Abstract ...................................................................................................................................... ii Table of Contents ..................................................................................................................... iii Acknowledgements ................................................................................................................ viii Abbreviations ............................................................................................................................ ix Chapter 1 Introduction 1.1 Homogeneous Ziegler-Natta Catalysts and the Discovery of Methylaluminoxane (MAO)........................................................................................................................................ 1 1.2 Characterization and Structure of MAO ........................................................................... 2 1.3 Polymerization Mechanisms ............................................................................................. 6 1.4 Deactivation Processes, Stabilization of Ion-Pairs in Solution and Chain Transfer reactions ................................................................................................................................... 10 1.5 MAO-ROBOTS project .................................................................................................. 12 References ................................................................................................................................ 12 Chapter 2 Studies on the Initial Reaction Steps of the Hydrolysis of TMA by 1H VT NMR 2.1 Introduction ............................................................................................................................. 17 2.1.1 Synthesis of MAO .................................................................................................... 17 2.1.2 Possible Reaction Mechanisms of the Hydrolysis of TMA ..................................... 18 2.2 Results and Discussion ............................................................................................................ 23 2.2.1 Quantitative 1H NMR ............................................................................................... 23 2.2.2 Determination of the Solubility of Water in Toluene by Quantitative NMR........... 23 2.2.3 Non-Molecularly Dispersed Water .......................................................................... 25 2.2.4 VT NMR Studies on the Hydrolysis Reaction of Trimethylaluminium ................... 27 2.2.4.1 Toluene as a Solvent .......................................................................................... 27 2.2.4.2 VT 1H NMR Experiments in Toluene: Approach A .......................................... 28 2.2.4.3 VT 1H NMR Experiments in Toluene: Approach B........................................... 37 2.2.4.4 VT 1H NMR Experiments in THF ..................................................................... 42 2.3 Conclusions ............................................................................................................................... 52 iii 2.4 Experimental ............................................................................................................................. 54 2.4.1 General Procedures and Materials............................................................................ 54 2.4.2 Determination of the Solubility of Water in Toluene by Quantitative NMR........... 54 2.4.3 Non-Molecularly Dispersed Water .......................................................................... 55 2.4.4 VT NMR Studies on the Hydrolysis Reaction of Trimethylaluminium .................. 55 2.4.5 Additional Experiments............................................................................................ 56 References ........................................................................................................................................... 57 Chapter 3 Studies on the Initial Reaction Steps of the Hydrolysis of TMA by Matrix Isolation Infrared Technique 3.1 Introduction ..................................................................................................................... 59 3.1.1 Infrared Matrix Isolation Spectroscopy.................................................................... 59 3.1.2 Matrix Isolation Studies and Trimethylaluminium ................................................... 61 3.2 Results and Discussion ................................................................................................... 63 3.2.1 General ..................................................................................................................... 63 3.2.2 Deposition of TMA in Argon Matrix ....................................................................... 64 3.2.3 Co-deposition of TMA and Water in Argon Matrix ................................................ 73 3.2.4 Co-deposition of TMA and Water (without inert gas) ............................................. 85 3.3 Conclusions ..................................................................................................................... 95 3.4 Additional Information ................................................................................................... 97 3.5 Experimental ................................................................................................................. 105 3.5.1 General Method ...................................................................................................... 105 3.5.2 Deposition of TMA in Argon Matrix ..................................................................... 109 3.5.3 Co-deposition of TMA and Aater in Argon Matrix ............................................... 111 3.5.4 Co-deposition of TMA and Water (without inert gas) ........................................... 112 References .............................................................................................................................. 113 Chapter 4 Quantification of Lewis Acidic Sites of Methylaluminoxane (MAO) by NMR Spectroscopic Techniques 4.1 Introduction ................................................................................................................... 115 4.1.1 Determination of TMA in MAO ............................................................................ 115 iv 4.1.2 Other Lewis Acidic Sites on MAO ........................................................................ 117 4.2 Results and Discussion ................................................................................................. 118 4.2.1 VT NMR Studies of an MAO Solution in Toluene