No description available.

No description available.

Universiẗat, Diss., 2001--Kaiserslautern.

Universiẗat, Diss., 2003--Würzburg. / Erscheinungsjahr an der Haupttitelstelle: 2002.

No description available.

L’objectif de cette thèse était de concevoir denouveaux matériaux polymères hydrophobes pour la protectionde composants semi-conducteurs, résistants à hautetempérature, aux forts champs électriques et aux atmosphèresagressives. Dans ce contexte, les polyimides d’addition sontapparus comme la famille de polymères la mieux adaptée pourl’application envisagée. La synthèse de l’encapsulant étantréalisée directement dans les boîtiers des modules, elle ne peutdonc pas contenir de solvant organique exogène. Ainsi, nousavons développé de nouvelles voies de synthèse sans solvantde poly(aminobismaléimide)s et de poly(bismaléimide)s.Dans un premier temps, différentes diamines aliphatiques ontété utilisées comme solvant réactif lors de la synthèse depoly(aminobismaléimide)s à une température bien inférieure à latempérature de fusion du bismaléimide utilisé (Tf > 300 °C). Unepremière série de 3 nouveaux poly(aminobismaléimide)sréticulés de 70 à 95 % a ainsi été réalisée. A partir de cespremières synthèses, 10 nouveaux poly(aminobismaléimide)sont été élaborés. Pour 9 d’entre eux, des diamines aromatiquesont été utilisées et, pour le dernier, une diamine siloxane. Cesrésultats démontrent la possibilité de généraliser ce procédé desynthèse.Dans un second temps, des poly(bismaléimide)s ont étésynthétisés, toujours sans solvant. Pour cela, les synthèses dequatre nouveaux bismaléimides liquides à température ambianteont été mises au point. Ces composés ont une structurealiphatique ou siloxane dans laquelle un motif pyroméllitique aété, ou pas, introduit. Leur polymérisation amorcée avecl’amorceur radicalaire ad hoc, conduit à la formation desmatériaux sans l’usage de solvant.Selon le choix des réactifs, des matériaux thermodurcissablesou élastomères sont obtenus. Ces derniers semblent mieuxadaptés à l’application souhaitée car, d’une part, la faibleviscosité des mélanges réactionnels permet leur applicationsans difficulté dans un module de puissance et, d’autre part, leurcaractère hydrophobe est plus marqué. L’un d’eux présente unestabilité thermique à 250 °C particulièrement intéressante et unetempérature de relaxation mécanique quasi hors gamme detempérature de fonctionnement. Ce matériau peut doncvraisemblablement être utilisé comme encapsulant. / The aim of this work is to develop new hydrophobicpolymeric materials for the protection of semi-conductorcomponents. These materials must withstand high temperature,strong electric fields and aggressive atmospheres such asmoisture. In this context, addition polyimides emerged as themost suitable polymers for the intended application. Thesynthesis of the encapsulant being made directly in the powermodules, it must be solvent free. Thus, we have developed newsolvent free synthesis routes of poly(aminobismaleimide)s andpoly(bismaleimide)s.First of all, different aliphatic diamines were used as a reactivesolvent in the synthesis of poly(aminobismaleimide)s to atemperature well below the melting point of the usedbismaleimide (m.p. > 300 °C). A first series of 3 newpoly(aminobismaleimide)s, crosslinked from 70 to 95 %, hasthus been made. From these first syntheses, 10 newpoly(aminobismaleimide)s have been developed. For 9 of them,aromatic diamines were used and, for the latter, a siloxanediamine. These results demonstrate that this process can begeneralized.Secondly, poly(bismaleimide)s were synthesized, still withoutany solvent. In order to do so, the syntheses of four newbismaleimides, liquid at room temperature, have beendeveloped. These compounds have an aliphatic or siloxanestructure in which a pyromellitic pattern has been or notintroduced. Their polymerization initiated with the suitable radicalinitiator leads to the formation of materials without the use of anysolvent.Depending on the choice of reagents, thermosetting materials orelastomers are obtained. These latter seem more suitable for thedesired application because, on one hand, the low viscosity ofthe reaction mixtures enables their application in a powermodule without any difficulty and, on the other hand, theirhydrophobic behaviour is stronger. One of them has aparticularly attractive thermal stability at 250 ° C and amechanical relaxation temperature almost out of the workingtemperature range. Therefore, this material may be used asencapsulant.

Neste trabalho, materiais nanocompósitos de poli(imida) (PI) derivada de BTDA-pFDA-Mel e argila do tipo montmorilonita, organicamente modificada (O-MMT), foram sintetizados usando a metodologia de two-steps. O componente inorgânico do nanocompósito foi adicionado nas concentrações de 3,3, 5,3 e 8,3% em massa. As membranas sintetizadas foram caracterizadas por Espectroscopia de Absorção na Região do Infravermelho com Transformada de Fourrier (FTIR), Difração de Raio X (DRX), Termogravimetria (TG), Espectroscopia de Fotoelétrons Excitados por Raio X (XPS) e Microscopias Ótica (MO), Eletrônica de Varredura (MEV) e de Transmissão (MET). Os resultados comprovam a formação de PI e uma estrutura de nanocompósito do tipo intercalado, onde a cadeia polimérica expulsa o surfactante do espaço interlamelar; além de apresentar estruturas de argila parcialmente esfoliadas. Os materiais sintetizados foram avaliados como polieletrólito em célula a combustível alcalina (Alkaline Fuel Cell - AFC), obtendo condutividades iônicas em torno de 0,032 S cm-1 e de 0,017 S cm-1 para as membranas de PI pura e de nanocompósito com 3,3% de argila em massa, respectivamente, ambas a 60 °C, as quais são na ordem ou até mesmo superior que os polieletrólitos comercias (Tokuyama®, 0,014 S cm-1) para eletrólito alcalino. Apesar de condutividades razoáveis, a performance obtida para as AFCs em operação não foram satisfatórias, desta forma, membranas de nanocompósitos com PI de cadeia principal de maior mobilidade foram sintetizadas, caracterizadas e avaliadas nas AFCs. Ademais, neste segundo nanocompósito, a adição de grupamentos amino na cadeia principal foram realizados para aumentar a condutividade iônica. Assim, este segundo material apresentou uma maior performance nas AFCs quando comparado com o nanocompósito de PI de cadeia mais rígida e com a membrana comercial Tokuyama® nas mesmas condições. Além disso, a carbonização superficial das amostras foi realizada por meio de tratamento térmico. A formação de estruturas grafitizadas nos materiais de PI pura e dos nanocompósitos foram investigadas por FTIR, DRX, TG, XPS e EPR. Foi encontrado que a formação de estruturas do tipo grafite nas amostras ocorrem principalmente nas primeiras camadas (grafitização superficial), preservando a estrutura interna da poli(imida). Com isso, estruturas poliméricas ou nanocompósitos com superfícies grafitizadas podem atuar tanto como polieletrólitos e ser um caminho promissor para o desenvolvimento de arranjos eletrodo-membrana (Membrane Electrode Assembly - MEA) mais eficientes para células a combustíveis alcalinas, como em processos de catálise heterogênea e processos de separação com membranas. / In this work, Poli(imide)/clay (PI/clay) nanocomposite membranes were synthesized by employing a two-steps method using organically modified montmorillonite clay (O-MMT) with different amounts of O-MMT loading (3.3, 5.3 and 8.3 wt.%). Fourier transform infrared spectroscopy (FTIR), X-ray power diffraction (XRD), thermogravimetric analysis (TG), X-ray photoelectron spectroscopy (XPS), optical microscopy (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM) measurements, confirmed the formation of pure PI and intercalated-nanocomposite structures. The results revealed parallel clay layers with interlamellar PI and some organoclay partially exfoliated. In addition, the polyelectrolyte membranes of PI and PI/O-MMT (3.3 wt.%) showed that the ionic conductivity were 2- and 1-fold, respectively, higher than that of commercial membrane (Tokuyama®, 0.014 S cm-1), in alkaline fuel cells (AFC) at 60 °C. Despite the fact that the membranes of pure PI and PI/O-MMT demonstrated a good degree of ionic conductivity, rapid fuel cell performance deactivation occurred for the temperature higher than 75 °C. Furthermore, the lack of prepared polyelectrolyte ionic groups, led us to consider alternative synthesis of PI/clay nanocomposite membranes. Thus, the performance for second polyelectrolyte was superior when compared to pure PI, PI/O-MMT and commercial Tokuyama® membranes at same conditions. Moreover, the samples were also surface carbonized by thermal treatment. Combining FTIR, XRD, TG, XPS and electron paramagnetic resonance (ESR) analysis, the results suggested that graphitized nanostructures formation occurred mainly on the surface, maintaining the PI bulk structure. Therefore, graphitized PI/clay membranes may act as one promising way for enhancing both membrane electrode assembly in alkaline fuel cells and gas separation or catalysis.

This dissertation focuses on two different types of organometallic compounds, carbenes and imides. The first project deals with the archetypal Schrock carbene, and the second project studies complexes that contain metal-nitrogen bonds, both amides and imides. A summary of the research in this dissertation is discussed in Chapter 1. Chapter 2 begins the studies of the archetypal Schrock carbene (ButCH2)3Ta=CHBut. The studies include the synthesis of deuterated compounds (ButCD2)3TaCl2 and ButCD2Li, observation and identification of the intermediate, Ta(CD2But)5, and kinetic studies of the conversion of Ta(CD2But)5 to (ButCD2)3Ta=CDBut, giving the activation parameters and a kinetic isotope effect for the conversion. The work here confirms that the pentaneopentyltantalum is the precursor to the archetypal Schrock carbene. Chapter 3 studies the effects of isotopic substitution on NMR chemical shifts of complexes in Chapter 2. Conformations of (ButCD2)3TaCl2 and Ta(CD2But)5 have also been investigated. Chapter 4 begins the study of compounds containing metal-nitrogen bonds. Guanidinate imides Ta(NMe2)(=NSiMe3)[RNC(NMe2)NR]2 (R = Cy, Pri) have been prepared from the reactions of Ta(NMe2)4[N(SiMe3)2] with two equivalents of carbodiimides, RN=C=NR. The two guanidinate imides have been characterized by NMR spectroscopy and elemental analysis. In addition, the structure of Ta(NMe2)(=NSiMe3)[CyNC(NMe2)NCy]2 has been studied by single crystal X-ray diffraction. Under heating, Ta(NMe2)4[N(SiMe3)2] undergoes an unprecedented elimination of Me3Si-NMe2, converting the amide ligand –N(SiMe3)2 to the imide ligand =NSiMe3 to give an intermediate Ta(NMe2)3(=NSiMe3). In the presence of CyN=C=NCy, the carbodiimide captures the intermediate to give another intermediate Ta(NMe2)2(=NSiMe3)[CyNC(NMe2)NCy]. Subsequent second carbodiimide insertion leads to the formation of the final product Ta(NMe2)(=NSiMe3)[CyNC(NMe2)NCy]2. The remaining amide ligand, –NMe2, in Ta(NMe2)(=NSiMe3)[CyNC(NMe2)NCy]2 and Ta(NMe2)(=NSiMe3)[PriNC(NMe2)NPri]2 gives two separate resonances in the proton NMR spectrum at room temperature indicating inequivalence of the two methyl groups. The interconversion of the methyl groups in the former has been studied with variable-temperature NMR. Chapter 5 studies the synthesis and characterization of metal cage complexes [(Me2N)3MO]4 (M = Nb, Ta). Single crystal X-ray diffraction studies show a cubane-like structure with M-O bridges. Variable-temperature NMR of the inequivalent amide methyl groups –NMeAMeB has also been carried out to find the activation parameters for the exchange.

The iron-molybdenum cofactor (FeMo cofactor) is the catalytic center of nitrogen fixation in molybdenum-dependent nitrognease enzymes. The resting state cofactor is a complex [MoFe7S9X] cluster, in which the central ligand X is a central hexacoordinated monoatomic light atom (2p), and the exact identity of X is uncertain. The heteroligated, nitrogen-containing core environment of the cofactor cluster may also be relevant to active states, as several mechanistic proposals for cofactor catalysis incorporate substrate-derived nitrogenous moeities into the cluster core during turnover. To this end, we have explored synthetic pathways to the dinuclear and tetranuclear nitrogen-containing iron-sufur clusters, which may mimic the heteroligated core environment of the cofactor. Dinuclear iron-amide clusters Fe2(μ-NHtBu)2[N(SiMe3)2]2 (46) and Fe2(μ-NHtBu)2(μ-S)[N(SiMe3)2]2 (47) are useful precursors for the preparation of [Fe4(NtBu)n(S)4-nCl4]z cubane complexes that span all mixed imide/sulfide core compositions between the classic [Fe4S4] and the more recently reported [Fe4(NtBu)4] homoleptic motifs. The [Fe4NS3] core of the n = 1 cluster is particularly noteworthy in being essentially isometric with the analogous [Fe4S3X] subunit of the FeMo cofactor structure. Synthetic compounds are characterized by single crystal X-ray crystallography, cyclic voltammetry, and UV-Vis, 1H NMR spectroscopies.

The iron-molybdenum cofactor (FeMo cofactor) is the catalytic center of nitrogen fixation in molybdenum-dependent nitrognease enzymes. The resting state cofactor is a complex [MoFe7S9X] cluster, in which the central ligand X is a central hexacoordinated monoatomic light atom (2p), and the exact identity of X is uncertain. The heteroligated, nitrogen-containing core environment of the cofactor cluster may also be relevant to active states, as several mechanistic proposals for cofactor catalysis incorporate substrate-derived nitrogenous moeities into the cluster core during turnover. To this end, we have explored synthetic pathways to the dinuclear and tetranuclear nitrogen-containing iron-sufur clusters, which may mimic the heteroligated core environment of the cofactor. Dinuclear iron-amide clusters Fe2(μ-NHtBu)2[N(SiMe3)2]2 (46) and Fe2(μ-NHtBu)2(μ-S)[N(SiMe3)2]2 (47) are useful precursors for the preparation of [Fe4(NtBu)n(S)4-nCl4]z cubane complexes that span all mixed imide/sulfide core compositions between the classic [Fe4S4] and the more recently reported [Fe4(NtBu)4] homoleptic motifs. The [Fe4NS3] core of the n = 1 cluster is particularly noteworthy in being essentially isometric with the analogous [Fe4S3X] subunit of the FeMo cofactor structure. Synthetic compounds are characterized by single crystal X-ray crystallography, cyclic voltammetry, and UV-Vis, 1H NMR spectroscopies.