Item – Thèses Canada

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Numéro d'OCLC
916578948
Lien(s) vers le texte intégral
Exemplaire de BAC
Exemplaire de BAC
Auteur
Perry, Mitchell Robert,
Titre
Vanadium mediated radical polymerization.
Diplôme
M. Sc. -- University of Prince Edward Island, 2012
Éditeur
Ottawa : Library and Archives Canada = Bibliothèque et Archives Canada, [2013]
©2011
Description
2 microfiches
Notes
Includes bibliographical references.
Résumé
<?Pub Inc> The importance of controlled radical polymerization is growing as the demand for specific polymeric architectures with defined molecular weights and narrow polydispersity indices increases. While many techniques to realize this goal have been developed, the central facet of CRP aims to minimize the concentration of propagating radicals at any one time, thereby decreasing the probability of unwanted side reactions such as combination and disproportionation. Gaining many recent advances is the field of organometallic mediated radical polymerization, which utilizes an organometallic complex to impart control over the polymerization process. Metals, specifically cobalt, have shown efficacy in controlling a wide range of monomers. Vanadium has shown promise in controlling the polymerization of vinyl acetate (VAc), a notoriously difficult monomer to control. The system, comprised of a bis(imino)pyridyl ligand framework generates unprecedented control for vanadium, with excellent agreement between expected and experimental molecular weights having narrow distributions. However, control is lost and catalytic activity decreases after approximately three hours. This thesis details an investigation into the electronic and steric properties of the ligand, a bis(imino)pyridyl (BIMPY) framework, and its effect on the polymerization behaviour of the corresponding vanadium trichloride complexes. It is clear that variation at both the 'para' and ' ortho' positions of the aryl ring affects the polymerization behaviour, but this does not significantly alter the occurrence of catalyst death at run times longer than three hours. Improved control is obtained with increasing bulk present on 'ortho'-positions, but further attempts to increase the sterics at these positions have been unsuccessful. Computational studies conducted implicate radical attack on the backbone of the ligand framework in this catalyst death, supported experimentally. Complexes bearing various N='C' substituents were synthesized and screened, showing modest improvements over the parent system. Expansion of monomer scope to include other monomers was conducted, with vinyl esters giving the most promising results. This led to the investigation of vinyl fatty acids, a group of renewable monomers currently overlooked in the literature. Results from screening reactions with [BIMPY]DippVCl 3 suggest that catalyst death is still a factor, with low conversions and modest control being obtained. Further investigations were made into a more robust cobalt system, Co(acac)2. High conversions were obtained but control remained elusive, justified by the inherent large size of the monomers being incompatible with the known reaction mechanism.
ISBN
9780494940495
0494940492