Freiburg (Breisgau), Universiẗat, Diss., 2001.

Halle, Wittenberg, University, Diss., 2001.

Freiburg (Breisgau), Universiẗat, Diss., 2002.

Bielefeld, University, Diss., 2003.

Thesis (Ph. D.)--University of Oregon, 2006. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 219-228). Also available for download via the World Wide Web; free to University of Oregon users.

L’étude réalisée porte sur la caractérisation d’un matériau polymère, le polyamide 12. Le matériau en question est utilisé dans des procédés industriels sous la forme de poussières pour réaliser des pièces mécaniques par frittage laser. De plus, une étude du polyméthacrylate de méthyle, polymère plus connu, a été conduite en parallèle afin de valider nos résultats expérimentaux. La première partie de l’étude porte sur la caractérisation du matériau et l’étude de sa dégradation thermique lorsqu’il est soumis a un échauffement lent. Une étude calorimétrique a tout d’abord été réalisée afin de comprendre le comportement global du matériau et identifier les grandes étapes de la dégradation thermique (changements de phases, réactions globales). Puis une analyse thermogravimétrique a été conduite afin de déterminer les étapes de dégradations identifiables par la variation de masse des échantillons. Afin de confirmer les étapes de la dégradation, nous avons analysé les gaz émis lors de la dégradation. Enfin, ces résultats ont été corrélés a des estimations obtenues par une méthode de contribution de groupes. La seconde partie concerne le risque d’allumage d’explosions de poussières de polymères. Une étude des énergies permettant l’allumage de réactions explosives est importante afin d’assurer la sécurité des chaines de production. Outre l’obtention d’énergies d’allumage de flammes dans un nuage de poussières, des relevés de pression en bombe sphériques ont également été faits, ainsi qu’une visualisation directe de la flamme d’un nuage de polymère. L’ensemble de ces résultats est important dans le domaine de la sécurité, tant dans le domaine des incendies que de la sécurité industrielle. / This work deals with a polymer characterization, the polyamide 12. This polymer may be used as a dust in industrial processes to create mechanical pieces by laser sintering. Methods and experimentations we applied to this study are compared to polymethylmethacrylate, a well-known polymer, for validation. In a first part, characterization of polymer has been performed (phase changes enthalpies and temperatures) through differential scanning calorimetry and thermogravimetric analysis. During these analysis, gas phase chromatography has been made to investigate pyrolysis and oxidation gaseous products. So a kinetic study has been performed to obtain global reactions involved in the thermal degradation process of polyamide 12. These results are useful to point the main reactions involved in thermal degradation. Then, all the results have been compared to some obtained by estimative methods, which can give some clues about physical and chemical properties of materials through their molecular structures. The second part of the work deals with dust explosions, energies needed to create flames in polymer dust clouds and the violence of explosions. Pressure evolutions versus time have been measured. Flame visual records by high speed camera have also been performed. These results are useful for risk assessment in processes and for enclosure fires.

No description available.

This thesis describes efforts in theoretical prediction of the macrostructures of poly(norbornadienes) and poly(norbornenes). In contrast to existing synthetic helical polymers such as poly(isocyanides) and poly(methacrylates), the helical parameters of norbornene and norbornadiene polymers may be tunable by judicious choice of substituents. Computer modelling surveys were carried out to qualitatively compare effects from tacticity, steric bulk, pi-stacking and hydrogen-bonding on polymer topology. Models capable of pi-stacking and hydrogen-bonding displayed interactions between substituents on neighbouring repeat units. These modelling studies suggest that helical turns will collapse to form and enforce a tube-like structure. Polymers of functionalized norbornenes and norbornadienes were produced using different achiral and racemic catalysts. Microstructural characterization was conducted by 1H, 1H-1H COSY and 13C{1H} NMR spectroscopy. The tacticities of poly(norbornadienes) agreed well with literature reported values of the catalyst used. However, all three poly(norbornenes) had the same tacticity. Macrostructural characterization was accomplished by GPC, LS, polarimetry and CD spectroscopy. All polymers had a spherical conformation in solution. Polymers made of optically active monomers were optically active whereas polymers made of non-optically active monomers were not.

The effects of different donor atoms of the supporting ligands (i.e. oxygen and nitrogen donor ligands) are at the root of this study as well as an attempt to improve our understanding of the catalyst/co-catalyst interaction. Simply based on the lack of knowledge in the area of vanadium polymerization mechanism our group has set out to investigate possible activation pathways through a series of alkylation reactions to assess the vanadium-carbon bond stability by using a variety of oxygen and nitrogen donor-based supporting ligands. Upon using alkylating agents such as the alkylaluminium co-catalysts, attempts to trap and crystallize the active intermediate were attempted only to elucidate the deactivation process. Insight into the activation and deactivation pathways of vanadium-based catalysts and a few other metal congeners such as zirconium, chromium, and manganese will be investigated in the following thesis. The second chapter will cover insight into the activation and deactivation pathways of the industrially used tris(acetylacetonato) vanadium complex in the copolymerization of ethylene and propylene forming a polymer used in the production of synthetic rubber. In attempt to combine the migratory properties of the oxygen donor based ligands and the stabilization properties nitrogen donor based ligands, the reactivity of the acetylpyrrolide ligand system was investigated with V(III). Two novel organometallic complexes were synthesized where, in one case, vanadium(III) mediated an aldolic condensation of the acetylpyrrolide ligand and in a second case a vanadium(II) metal centre promoted a pinacolic coupling of the ligand (Chapter 5). Chapter 6 in mainly focused on the vanadium/aluminium interaction and the role of the co-catalyst in the activation and deactivation of the vanadium metal centre. In this case the vanadium centre is supported by the bulky N,N,N, tris-trimethylsilyl diethylenediamidoamino ligand. Formation of novel vanadium/aluminium clusters were synthesized and have given great insight into the vanadium/aluminium interaction and have demonstrated involvement of the ligand as seen previously in the case of the bis(imino)pyridyl ligand system. Preliminary reactivity of the meso-diphenyldipyrrolemethane ligand was investigated with Zr(IV), V(III), Cr(III), Cr(II) in Chapter 7. These reactions revealed the possible bonding modes of the pyrrolide moiety with the metal centre. Treatment of the V(III) meso-diphenyldipyrrolidemethane complex with a sterically demanding aryloxide led to an interesting deoxygenation reaction of the aryloxide to form an oxygen bridged vanadium dimer which exerted high polymerization activities upon activation with dimethylaluminiumchloride. (Abstract shortened by UMI.)

The work presented in this thesis deals primarily with living free radical polymerization (LFRP). Two main specific areas of this process have been studied; thermal and photochemical reaction sequences. Stoichiometric unimolecular initiators were found to be ideal probes for studying the reactions involved in the LFRP process. The bond dissociation energy (BDE) of the labile C-O bond of the alkoxyamine initiators was found to be ca. 28 kcal/mol and is dependent on the resulting carbon centered radical produced upon thermal decomposition. Lower activation energies were measured for more stable carbon centered radicals. Complementary to the thermal studies, photoacoustic studies (PAC) involving photochemical decomposition of the initiators led to the homolytic N-O and C-O bond cleavages in addition to disproportionation product formation. The BDE for the N-O bond of these initiators is ca. 43 kcal/mol. These studies also provided insight into volume effects, where a strict homologous solvent series is not required for extrapolating true enthalpies of reactions and volume correction factors for PAC. The decomposition quantum yields of a series of ketone based actinometers used for PAC BDE studies were re-evaluated and found to be solvent independent. The specific kinetics of thermal LFRP were equally investigated through the use of probes which are normally used for thermal initiation. Fast time resolved techniques of laser flash photolysis (LFP) were used to measure the bi-molecular rate constant for the coupling reaction between a carbon centered radical and a nitroxide radical involved in LFRP. Typical values lay in the area of 108 M-1 s-1 and are influenced by the structure of the carbon centered radical and not that of the nitroxide. The rate constants were observed to be slower with more stable carbon centered radicals, similar to the BDE results where weaker dissociation energies were observed. The formation of minor disproportionation products upon thermal decomposition of the unimolecular initiators was assigned to a concerted four center elimination ultimately responsible for the lack of controlled polymerization with acrylates. The incorporation of steric effects into the monomer or the nitroxide suppressed the formation of these products by increasing the energy barrier necessary for correct orbital alignment required for the elimination reaction. Living polymerization of acrylate monomers was achieved with a nitroxide containing bulky substituents in its 2 and 6 positions. Moderate success of living polymerization was also achieved with acrylate type monomers through the use of an additional phase not miscible with the bulk phase. Chromophores producing triplet states upon excitation were found to undergo fast and efficient energy transfer to a covalently linked alkoxyamine subsequently promoting C-O bond homolysis. The orientation of the C-O bond relative to the chromophore in addition to the distance separating the two influences the efficiency of energy transfer and bond cleavage. Using a benzophenone type chromophore with a covalently linked alkoxyamine initiator promoted photoinduced living type polymerization of acrylate.