Baker, Joseph Hugh Franklin (2017-12). Tetraphosphine Linkers for Immobilizing Catalysts and Studies of Polymer Degradation Mechanisms. Doctoral Dissertation.
The overall goal of the first project of this thesis was to find ways to improve homogeneous catalysts and render them more recyclable and thus improve their lifetimes. One way to generate such superior catalysts is to whether them to solid, insoluble supports. The nature of the latter is crucial for the activities and lifetimes of the catalysts. Flexible linkers such as long alkyl chains allow contact of the catalysts with the surface and potentially their decomposition. Tetraphosphine linkers with rigid tetraphenylelement cores had been immobilized previously. The rigid nature of the scaffold ligands prevented interactions with the reactive surface and led to an immobilized Wilkinson's catalyst that could be recycled many times in a batchwise manner. In this new project, in order to test whether further increasing the distance between the immobilized catalyst and the surface would improve the lifetime of the catalysts, biphenyl spokes have been incorporated into the tetraphosphine linkers. The catalytic activity of these new catalysts compares favorably with that of previously used flexible linkers. In the second project of this thesis polyetheretherketone (PEEK) polymers, which are utilized in applications of extreme service environments in the oil and gas industry, are studied. PEEK material is rather tolerant of high temperatures and pressures and chemically comparatively resistant. However, PEEK degrades quite rapidly in the commonly used ZnBr? containing completion fluids, in combination with the high temperatures and pressures needed for hydraulic fracturing. The degradation of the polymer leads to machine parts breaking during the operation and results in costly delays in the drilling process. Therefore, the main goal of the second project of this thesis was to elucidate the molecular mechanisms that lead to the degradation of the polymer, and to define the factors that influence these decomposition pathways. Mechanistic studies after the identification of the small molecules produced, reveal the simultaneous occurrence of several decomposition pathways. The initial reaction in the PEEK polymer is the C-C bond cleavage at the ketone position. Subsequently, bromination by the ZnBr? in the completion fluids, other radical based decompositions, and hydrolysis under the acidic conditions take place.