Universiẗat, Diss., 2004--Frankfurt (Main).

Neste trabalho, descrevemos os conceitos de alinhamento e orientação baseados no formalismo de Fano e Macek e estudamos a fotoionização do estado fundamental do átomo de Hélio. Para isso usou-se uma função de onda aproximada obtida a partir da diagonalização do operador de Gailitis- Damburg. A anisotropia do sistema formado após a colisão foi caracterizada através do cálculo da densidade eletrônica do íon e através do tensor de alinhamento e do vetor de orientação. O comportamento destes parâmetros para as transições n? -> 1s e n->n-1 em função de n (número quântico principal do íon) foi graficado para as duas simetrias relevantes, 1P° e 3P°. Observamos que o alinhamento máximo do sistema, em relação ao eixo de maior simetria definido como sendo o eixo z ocorre no limite de Wannier (n-> ?). Nesta situação o elétron iônico se encontra ao longo do eixo z para a simetria 3 P° e perpendicular ao eixo z para a simetria 1 P°. Esse fenômeno é causado pela interação elétron-elétron / In this work we describe the concepts of aligrnment and orientation based on the formalism of Fano and Macek formalism and we study the photoionization of the Helium atom ground state. We have used an approximate wave function obtained from the diagonalization of the Gailitis- Damburg operator. The anisotropy of the system formed after the colision was measured through the calculation of the ion electronic density and also by the use of the alignment tensor and orientation vector. The behaviour of these parameters for the transitions np ->1s and n ->n-1 as a function of n (the principal quantum number of the ion) was plotted for both the relevant symmetries, 1 P° and 3 P°. We have observed that the maximum alignment of the system, with respect to the dominant symmetry axis defined as the z axis, occurs in the Wannier threshold (n->?). This leads to the alignment of the ionic electron along the z axis for the 3 P°symmetry, and orthogonal to the z axis for the 1P° symmetry. This phenomenom is caused by the electron-electron Ínteraction.

A new method for the synthesis of naphthalenes has been recently discovered. The Atom Transfer Radical Cyclisation (ATRC) of diverse 2-allylphenyl2',2',2'-trichloroacetates in the presence of a Cu complex afford schloronaphthalenes in good yields using either microwave or thermolytic methods of activation. A mechanism for the benzannulation reaction is proposed and experiments presented in order to validate this hypothesis. The use of 1,3-bis(2,6-diisopropylphenyl)imidazolium copper(I) chloride [(IPr)CuCl)] along with other metal carbenes is compared to the already reported CuCl/ligand system. Since the scope and synthetic utility of this new benzannulation reaction is restricted due to the use of the MW reactor, a solvent in which the thermal reaction can take place is reported, proving its efficiency in the synthesis of a range of substituted naphthalenes. The potential and versatility of the benzannulation reaction has been investigated. Studies towards the synthesis of gilvocarcin M which contains a tetracyclicaromatic core are presented. Gilvocarcins have potential use as anti-cancer agents and represent a member of the C-aryl glycosides found in natural products. Gilvocarcin M is a challenging target because there are a sparse number of total syntheses reported in the literature. The ATRC reaction of (vinyl)phenyl trichloroacetate has also been investigated, affording the synthesis of functionalised coumarins. The mechanism of this reaction has also been investigated, establishing that, in some cases, aretro-Kharasch reaction is observed.

Abstract: Styrene and methyl methacrylate have been polymerized successfully through atom transfer radical polymerization (ATRP) in aqueous dispersed media (emulsion ATRP). The thesis is divided into four experimental parts. In the first part, a water-soluble initiator was prepared for emulsion ATRP and utilized under various conditions in the presence of two ligands N, N, N’, N’’, N’’-Pentamethyldiethylenetriamine and 2,2’-bipyridine to attain activation/deactivation only in the oil phase with Tween 20 as a non-ionic surfactant. The initiator was synthesized by the reaction of diethanolamine with α-Bromoisobutyryl bromide in anhydrous tetrahydrofuran. 1H NMR spectroscopy (500 MHz, deuterium oxide, or chloroform-d) was performed to confirm the successful synthesis of the initiator and polystyrenes. In the second and third parts, two commercial initiators were used, poly(ethylene glycol) methyl ether 2-bromoisobutyrate (Mn= 2000 g/mol), and 2-hydroxyethyl 2-bromoisobutyrate (Mn= 211.05 g/mol). BPY, tris(2-pyridylmethyl) amine and 4, 4’-dinonyl -2, 2’-dipyridyl were used as the ligands with various molar ratios. Polyoxyethylene (80) sorbitan monooleate, and polyoxyethylene (20) oleyl ether were used as non-ionic surfactants. In the fourth part, a macroinitiator was synthesized by the reaction of polyoxyethylene (20) stearyl ether with α-Bromoisobutyryl bromide. The formation of the macroinitiator as well as the successful synthesis of poly(ethylene glycol)-b-polystyrene, and poly(ethylene glycol)-b-poly(methyl methacrylate) block copolymers were confirmed by Fourier transform infrared and 1H NMR spectroscopies. The molecular weight of the resulting polymers, as well as the stability of the emulsion systems, were evaluated by gel permeation chromatography and dynamic light scattering, respectively.

The presence of and interactions between structural defects, fluids, and trace elements during deformation play a vital role in the manner in which materials respond to an applied stress. Although the links between crystal defects and trace element mobility have been lying at the frontier of research in Earth sciences, the role of fluids and the underlying physico-chemical processes linking them remain poorly understood. Investigation of these nanometer scale processes requires a correlative approach combining high-spatial resolution analytical techniques. This thesis integrates novel 2D and 3D structural and geochemical mapping methods such as electron channeling contrast imaging, electron backscatter diffraction, scanning transmission electron microscopy (STEM) and atom probe tomography (APT) to interrogate the atomic structure and composition of geomaterials in an attempt to better understand long-standing questions in Earth sciences and build bridges between materials science and geoscience. The processes investigated in this thesis include: 1) the underlying diffusion processes that mobilize trace elements into deformation-induced nanostructures; 2) the mechanisms of trace element segregation associated with fluid inclusions; 3) the influence of fluid inclusions on the mobility of structural defects and trace element mobility; and 4) the initial stages of bubble nucleation in the presence of nanoscale chemical heterogeneities. Ultimately, this research interrogates the feedbacks between deformation and trace element diffusion processes, fundamentally investigating their impact on rheology. More specifically, the thesis investigates the influence of deformation and associated nanostructures on the remobilization of trace elements and, in turn, the influence of trace elements on the nucleation and mobility of nanostructures. The combined work successfully identified two diffusion mechanisms for deformation-induced trace element mobility, characterized fluid-inclusions in APT data, documented two processes that led to proposing a new fluid inclusion-induced hardening model, and documented direct evidence of bubble nucleation on the surface of nanoscale chemical heterogeneities. This work not only pushes the limits of high-spatial resolution analytical techniques including STEM and APT, but the results have significant transdisciplinary implications in the fields of geoscience, materials science, engineering, and analytical microscopy.

In the first Chapter, Polyhomologation, a powerful technique to synthesize well-defined, perfectly linear, polyethylenes with controllable molecular weight, topology and low polydispersity, is presented in the first Chapter. In this Chapter is also discussed the combination of polyhomologation with other polymerization techniques such as Ring Opening Polymerization, ROP, Atom Transfer Radical Polymerization, ATRP, as well as with chlorosilane linking chemistry towards well-defined polyethylene-based macromolecular architectures. In the second Chapter, α,ω-dihydroxy-polyethylene was synthesized by the polyhomologation of dimethylsulfoxonium methylide with 9-thexyl-9-BBN (9-BNN: 9-borabicyclo[3.3.1]nonane), a novel difunctional initiator produced from 9-BBN and 2,3-dimethylbut-2-ene with two active and one blocked sites, followed by hydrolysis/oxidation. The terminal hydroxy groups were used either directly as initiators, in the presence of 1-tertbutyl-2,2,4,4,4-pentakis(dimethylamino)-2λ5,4λ5-catenadi(phosphazene) (t-BuP2), for the ring opening polymerization of ε-caprolactone, ε-CL, in order to afford polycaprolactone-b-polyethylene-b-polycaprolactone (PCL-b-PE-b-PCL) or after transformation to ATRP initiating sites in order to polymerize styrene and produce polystyrene-b-polyethylene-b-polystyrene (PSt-b-PE-b-PSt) triblock copolymers. Molecular characterization by 11B, 13C and 1H NMR as well as FTIR, and high-temperature GPC (HT-GPC) confirmed the well-defined nature of the synthesized new difunctional initiator and triblock copolymers. Differential scanning calorimetry was used to determine the melting points and degree of crystallinity of PE and PCL. In the third Chapter, a novel triallylborane initiator was synthesized and used to afford α-allyl-ω-hydroxy-polyethylene by polyhomologation of dimethylsulfoxonium methylide. The α-allyl-ω-hydroxy-polyethylene was then used as a macroinitiator (OH group) for the ROP of ε-CL and LLA to afford well-defined triblock terpolymer of polylactide-b-polyethylene-b-polycaprolactone (PLLA-b-PE-b-PCL). The characterization of all intermediate and final products by 1H NMR, FTIR, and HT-GPC, verified the well-defined nature of the triblock terpolymer. In the fourth Chapter, polyethylene (PE)-based 3- and 4-miktoarm star [PE(PCL)2, PE(PCL)3], as well as H-type [(PCL)2PE(PCL)2] block copolymers (PCL: polycaprolactone), were synthesized by combining polyhomologation, chlorosilane chemistry, and Ring Opening Polymerization (ROP). For the synthesis of miktoarm stars, a hydroxyl-terminated PE-OH, prepared by polyhomologation of dimethylsulfoxonium methylide with a monofunctional boron initiator, reacted with either chloromethyl(methyl)dimethoxysilane or chloromethyltrimethoxysilane. After the hydrolysis of the methoxysilane groups, the produced difunctional or trifunctional macroinitiators were used for the ROP of ε-caprolactone, in the presence of 1-tert-butyl-2,2,4,4,4-pentakis(dimethylamino)-2λ5,4λ5-catenadi(phosphazene)(t-BuP2). The H-type block copolymers were synthesized using the same strategy but with a difunctional polyhomologation initiator. All intermediates and final products were characterized by HT-GPC, 1H NMR, and FTIR analysis. The thermal properties of the PE precursors and final products were studied by DSC and TGA. In the fifth Chapter, the self-assembly properties of the amphiphilic linear block copolymer PE-b-PCL and 3-miktoarm star copolymers (PE-b-PCL2) were studied in THF, a selective solvent for PCL, by Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM) and Atomic Force Microscope (AFM). All the above findings presented in this dissertation emphasize the utility of polyhomologation for the synthesis of well-defined polyethylene-based complex macromolecular architectures, which is practically impossible through another kind of polymerization, including the catalytic polymerization of ethylene. In the sixth Chapter, the summary of the thesis and some consideration on the subjects of future work are given.

No description available.

<p> A thermodynamic investigation of interactions between solute atoms and defects (other solute atoms, electrons, phonons, and grain boundaries) has been conducted by solubility measurements of copper and gold in silicon and germanium. The major objective of the investigation was to gain a further understanding of the physical state of solute atoms and their interactions with defects in homopolar crystals. An attempt was also made to extend the theory and experimental results of equilibrium studies to kinetic phenomena associated with device manufacture. An experimental study of the kinetics of solute precipitation at dislocations was also carried out by electrical conductivity measurements. </p> <p> Original contributions which have been obtained from the results of this program are listed below. </p> <p> (1) The relative partial molar enthalpies and entropies of solution for the various systems are </p> <p> ∆Ħ_Cu (in Si)=37.3±0.5 Kcal./mole, ∆S⁻ᵉˣ_Cu(in Si)=7.1±0.4 cal./mole-ºK, </p> </p> ∆Ħ_Cu (in Ge)=41.3±0.7 Kcal./mole, ∆S⁻ᵉˣ_Cu(in Ge)=10.3±0.6 cal./mole-ºK, </p> <p> ∆Ħ_Au (in Si)=43.8±1.4 Kcal./mole, ∆S⁻ᵉˣ_Au(in Si)=6.8±1.0 cal./mole-ºK, </p> <p> ∆Ħ_Au (in Ge) ≳ 45 Kcal./mole, and ∆S⁻_Au(in Ge) ≳ 15 cal./mole-ºK. </p> <p> The partial molar enthalpy and entropy of copper in silicon with respect to Cu₃Si are 40.2±0.5 Kcal./mole and 9.7±0.5 cal./mole-°K, respectively. </p> <p> (2) Solubility measurements, metallography, and X-ray studies yielded evidence for delayed nucleation of intermediate compounds in copper-silicon diffusion couples. </p> <p> (3) The solubility of copper in vapor grown polycrystalline silicon is much greater than that in single crystal material below 800°C. The ratio of the grain boundary solubility to the single crystal solubility was estimated to be of the order of 5 x 10⁵. The high interaction energy between copper and grain boundaries in silicon (approximately 1.5 eV) was ascribed to chemical bonding. </p> <p> (4) Arsenic doping of germanium (such that the semiconductor remains intrinsic) enhances the solubility of copper in this material. This effect was quantitatively described by a theory of complex formation. </p> <p> (5) A study of the solubility of copper in p-type silicon indicated that copper is incompletely ionized in intrinsic silicon at elevated temperatures (≃1000°C). </p> <p> (6) The solubility of gold in silicon is decreased by boron doping, and this was explained on the basis of a low (less than unity) donor/acceptor ratio of substitutional gold. </p> <p> (7) The rate equation describing the precipitation of copper in silicon has a time exponent of 0.687±0.043. </p> <p> (8) Generalized phenomenological equations for ternary diffusion in covalent semiconductors were developed and it was demonstrated that information about diffusion phenomena may often be obtained from equilibrium measurements. </p> <p> (9) A quasi-steady state experiment was designed whereby copper segregated to regions of high boron concentration (in silicon) during a heat treatment operation, in qualitative agreement with theory. </p> / Thesis / Doctor of Philosophy (PhD)

<p> It has been shown that the hydroxy compounds la-4a possess triplet states which are substantially shorter-lived than those of their methoxy analogs (lb-4b). In each case the efficient quenching of the excited carbonyl triplet state has been attributed to intramolecular phenolic hydrogen abstraction. Evidence for this is found in the detection of biradical species generated from triplet decay, primary hydrogen-deuterium kinetic isotope effects and thermodynamic parameters which support both atom transfer (enthalpy) and high degrees of order (entropy) in the transition state necessary for the proposed abstraction process. The difference in triplet lifetimes (16 ns to 1135 ns) is due almost exclusively to varying degrees of difficulty in obtaining a transition state geometry in which the phenoxy hydrogen is properly lined up for intramolecular hydrogen abstraction. </p> / Thesis / Master of Science (MSc)

No description available.