Das dielektrische Verhalten von Polyäthern zwischen Mikrowellen- und Infrarot-Gebiet

Zusammenfassung Es wurde die Absorption und Dispersion verschiedener Polyäther im Mikrowellengebiet und im fernen IR untersucht. Mit wachsender Sauerstoffzahl in der Kette werden die Torsions- und Biegeschwingungen wachsend IR-aktiv. Ihre Frequenzlagen ändern sich mit dem zunehmend polaren Charakter der Struktur. Die Analogie zwischen der Verschiebung der Schwingungsfrequenzen und dem Verlauf der Schmelztemperaturen wird diskutiert.Mit zunehmend polarem Charakter steigen der Temperaturkoeffizient der Molpolarisation und die Differenz (–n ²) der Dielektrizitätskonstanten im Mikrowellengebiet und im optischen Bereich stark an. Ein Vergleich mit der Höhe der Dispersionsstufen im fernen IR und deren Temperaturabhängigkeit ergab, daß diese zusätzliche Polarisation nicht allein durch die IR-aktiven Banden bedingt ist. Sie muß gekoppelt sein mit dem ebenfalls stark anwachsenden Untergrundverlust im gesamten mm- und sub-mm-Gebiet.

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Summary Absorption and dispersion of several polyethers were measured in the microwave region and in the far infrared. The torsional vibrations become increasingly iractive with increasing number of oxygens in the chain. Their frequencies shift, too, in a manner analogues to the variation of the melting temperatures.The temperature coefficient of the mol polarization at 32 GHz and the difference (–n ²) between microwave and optical dielectric constant rise rapidly with increasing polar character of the structure. It was tried to correlate (–n ²) with the overall absorption of the skeletal vibrations. Height and temperature dependence of the far ir dispersion show, however, that the larger part of this additional polarization cannot be accounted for by the resonance absorption bands. It must be correlated with the background loss which extends over the whole mm and sub-mm range and also increases rapidly with increasingly polar structure.

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Mit 10 Abbildungen in 14 Einzeldarstellungen und 2 Tabellen     

Swelling effect onα-relaxation in high density polyethylene

Summary Swelling effects of carbon tetrachloride on the mechanical relaxations in the crystal mat and the melt-crystallized samples of high density polyethylene were studied using a torsion pendulum. A very strong-relaxation peak appears by swelling at the low temperature side of the original-relaxation for the crystal mat. It was shown that this strong-relaxation originates from the slippage between the highly swollen lamellae. For the melt-crystallized sample, the-relaxation peak is decreased by swelling, but its temperature is unchanged. This behavior suggests that the-relaxation in the melt-crystallized sample originates mainly from deformation process of intermosaic block region. The swelling effect on-relaxation was also discussed.

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Zusammenfassung Quellungseffekte von Tetrachlorkohlenstoff auf das mechanische Relaxationsverhalten in Einkristall-Matten und schmelzkristallisierten Proben von linearem Polyäthylen wurden mit den Torsionspendeln untersucht. Ein sehr starkes-Maximum tritt durch die Quellung bei tieferen Temperaturen als der der-Relaxation in den nicht gequollenen Einkristall-Matten auf. Es wird gezeigt, daß diese starke-Relaxation auf das Gleiten der ausreichend gequollenen Lamellen zurückzuführen ist. Bei schmelzkristallisierten Proben wird das-Maximum durch die Quellung erniedrigt, seine Temperaturlage wird jedoch nicht verändert. Dies zeigt, daß die-Relaxation in der schmelzkristallisierten Probe hauptsäcblich auf Deformations-Prozessen in den Blöcken beruht. Auch die Quellungseffekte auf die-Relaxationen wurden diskutiert.

     

Orbital correlation effects: The independent pair-potential approximation with application to the ground state and first ionized state of boron hydride

A new method is proposed for calculating correlation effects in atomic and molecular systems. The basis of the method is the formulation of a set of partial configuration expansions which yield directly variational orbital correlation corrections which are appropriately summed in order to obtain an estimate of the total correlation energy. This method is applied to the ground state of boron hydride and its cation at the equilibrium distance of BH. The results of the method are compared in detail with independent electron pair results and second order CI results. It is further shown that multiple substitutions are approximately accounted for in this method and the extent to which they are included is compared with other approximations. Finally, three methods of increasing accuracy, aimed at reducing the necessary computational effort, are given for determining the vertical ionization potential. The most economical method yields an IP of 9.70 eV or 0.03 eV less than the experimental IP. Completion of the basis is estimated to improve this value to 9.77 eV.     

Formation and Crystal Structure of [(F5TeOXe)+·SO2ClF][Sb(OTeF5)6-]

Xe(OTeF₅)₂ reacts with Sb(OTeF₅)₃ under the formation of [Xe₂(OTeF₅)₃]⁺[Sb(OTeF₅)₆]^-. From SO₂ClF solution a yellow solvate [F₅TeOXe]⁺·SO₂ClF· [Sb(OTeF₅)₆]^- is formed with the crystal data: a = 1028.1(1), b = 1040.9(1), c = 1780.2(3) pm, α = 98.07(1), β = 97.68(1), γ = 105.82(1)°, space group . The O-Xe···O fragment is essentially linear (176.1(2)°), and the two Xe-O distances are quite different 197.1(4) and 242.6(4) pm.     

Phosphine-mediated reductive condensation of gamma-acyloxy butynoates: a diversity oriented strategy for the construction of substituted furans

Exposure of gamma-acyloxy butynoates to stoichiometric quantities of triphenylphosphine results in reductive condensation to afford substituted furans, by way of allenic ester intermediates. As gamma-acyloxy butynoates are readily obtained through condensation of ethyl propiolate with aldehydes followed by acylation, this method represents a powerful and mechanistically novel protocol for the convergent three-component construction of substituted furans.     

Characterization and epitope mapping of two monoclonal antibodies against human CD99

CD99 plays a critical role in the diapedesis of monocytes, T cell differentiation, and the transport of MHC molecules. Engagement of CD99 by agonistic monoclonal antibodies has been reported to trigger multifactorial events including T cell activation as well as cell-cell adhesion during hematopoietic cell differentiation. In this study, to identify the functional domains participating in the cellular events, we mapped the epitopes of CD99, which are recognized by two agonistic CD99 monoclonal antibodies, DN16 and YG32. Using recombinant fusion proteins of GST with whole or parts of CD99, we found that both antibodies interact with CD99 molecules independently of sugar moieties. DN16 mAb detected a linear epitope located in the amino terminal region of CD99 while YG32 mAb bound another linear epitope in the center of the extracellular domain. To confirm that the identified epitopes of CD99 are actually recognized by the two mAbs, we showed the presence of physical interaction between the mAbs and the fusion proteins or synthetic peptides containing the corresponding epitopes using surface plasmon resonance analyses. The dissociation constants of DN16 and YG32 mAbs for the antigen were calculated as 1.27 x 10(-7) and 7.08 x 10(-9) M, respectively. These studies will help understand the functional domains and the subsequent signaling mechanism of CD99.     

Time dependence of viscosity of dilute polyisobutylene solutions

Summary Shearing at constant gradient of polyisobutylene (PIB) solutions in viscous polybutene oils results in time dependent changes of their viscosities. Two PIB fractions (M=8·10⁶ and 3.8·10⁶) have been studied in a variety of solvents, covering the viscosity range from 5 to 0.5·10⁻² poise. The overall phenomenon is similar to that already observed for polymethylmethacrylate, polystyrene, and polyethylene oxide solutions in Aroclor. Results have been discussed in terms of polymer molecular weight and concentration, solvent viscosity and gradient. The systems investigated are free from strong polar interactions and tendency toward molecular aggregation; time dependent changes of viscosity are therefore observable also for true molecularly dispersed solutions.

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Zusammenfassung Scherung mit konstantem Geschwindigkeitsgradienten von Polyisobutylen (PIB)-L?sungen in viskosen Polybuten-?len ergibt zeitabh?ngige ?nderungen ihrer Viskosit?ten. Zwei PIB-Fraktionen (M=8·10⁶ und 3,8·10⁶) wurden in einer Vielzahl von L?sungsmitteln untersucht, die den Viskosit?tsbereich von 5 bis 0,5·10⁻² Poise überdeckten. Das ph?nomenologische Erscheinungsbild ist ?hnlich dem schon beobachteten für Polymethylmethacrylat, Polystyrol und Poly?thylenoxid-L?sungen in Aroclor. Die Ergebnisse wurden hinsichtlich des Polymer-Molekulargewichts und der Konzentration, der L?sungsmittelviskosit?t und des Gradienten diskutiert. Die untersuchten Systeme sind frei von starken polaren Wechselwirkungen und von Tendenzen in Richtung auf molekulare Aggregation. Zeitabh?ngige ?nderungen der Viskosit?t sind deshalb auch für wahre molekulardisperse L?sungen beobachtbar.

     

Crystal structure, morphology and composition of magnetron sputtered tungsten carbide films

Summary It is shown that small variations of the deposition parameters during magnetron sputtering of tungsten carbide thin films may result in drastic changes of film properties. An increasing working gas pressure for example lowers stress and hardness values. Simultaneously, the texture of the WC_1–x cristallites turns from 200 preferential orientation to 111, whereas the composition of the films does not change. In reactive sputtering with a tungsten target there is a narrow range from 2 to 3% C₂H₂ gas admixture to the working gas where the films are stochiometric (WC) and hard, and grain size and morphology are similar to that of non-reactively sputtered films. The generation of different crystallite structures and orientations in the range of 0–3% C₂H₂ admixtures are used to produce a multiphase thin film with extremely low crack propagation.