Thermal density fluctuations in amorphous polymers as revealed by small angle X-ray diffraction

Summary Thermal density fluctuations in amorphous polymethyl methacrylate, polycarbonate and polyethylene terephthalate were studied by means of small angle X-ray scattering. The measurements were performed in a temperature range from 20 °C up to about 50 °C above the glass transition temperatureT _g of the individual sample.AboveT _g the experimental values of the fluctuations are proportional to the isothermal compressibility and the temperature of the sample as predicted by the fluctuation theory for a system in thermodynamic equilibrium.At temperatures belowT _g this relation is no longer correct. The experimentally determined fluctuations are now proportional to the compressibility of the sample in the equilibrium state atT _g and to the actual temperature of the glassy sample. By considering a statistical ensemble with exchange of energy, particles and order between the systems of the ensemble an equation can be derived for the fluctuations of the number of particles per given volume which predicts the observed behaviour. The order parameter takes into account the fact that the properties of the glassy state depend on the way by which the state was produced.

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Zusammenfassung Es wurden thermische Dichtefluktuationen in amorphem Polymethylmethacrylat, Polycarbonat und Polyäthylenterephthalat mit Hilfe der Röntgenkleinwinkelstreuung untersucht. Die Messungen erstrecken sich über einen Temperaturbereich von 20 °C bis zu etwa 50 °C oberhalb der GlastemperaturT _g der jeweiligen Probe.In Übereinstimmung mit den Ergebnissen der Fluktuationstheorie sind die Fluktuationen oberhalb vonT _g proportional zur isothermen Kompressibilität und zur Temperatur der Probe.Unterhalb der Glastemperatur ist diese Beziehung nicht mehr erfüllt. Hier ist die Fluktuation proportional zur Kompressibilität der Probe im Gleichgewichtszustand beiT _g und zur Temperatur. Auf der Basis einer statistischen Gesamtheit mit der Austauschmöglichkeit von Energie, Partikel und Ordnung zwischen den Systemen der Gesamtheit kann eine Beziehung für die Dichtefluktuation abgeleitet werden, die mit den experimentellen Ergebnissen übereinstimmt. Der zusätzliche Ordnungsparameter berücksichtigt die Tatsache, daß die Eigenschaften im Glaszustand wegabhängig sind.

     

Structure of 6-β-[(hexahydro-1H-azepin-1-yl)methyleneamino]penicillanic acid sulfoxide

The oxidation of 6--[(hexahydro-1H-azepin-1-yl)methyleneamino]penicillanic acid with potassium periodate or m-chloroperbenzoic acid leads to the corresponding sulfoxide. Its structure was proved by alternative synthesis by splitting out the N-phenylacetyl group from the benzylpenicillin sulfoxide and condensation of the 6-aminopenicillanic acid sulfoxide with N-formylhexamethyleneimine dibutylacetal.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 649–651, May, 1982.     

Spectrophotometric investigation of the reaction of eriochrome cyanin RC and magnesium and aluminium

The reaction of magnesium or aluminium ions with Eriochrome Cyanin RC in alkaline medium leads to formation of a complex of type ML. The molar absorptivities of the complexes are 1.90 +/- 0.14 x 10(3)1. mole(-1).cm(-1) at 570 nm for the magnesium complex and 3.87 +/- 0.04 x 10(4) at 555 nm for the aluminium complex. The conditional stability constants of the complexes were determined at various pH values, and hence the overall formation constants, which were found to be log beta(111) = 8.65 +/- 0.06 for MgOHL, log beta(121) = 22.29 +/- 0.05 for AlH(2)L, log beta(111) = 18.25 +/- 0.14 for AlHL, and log beta(101) = 13.66 +/- 0.01 for AlL.     

Carbon suboxide and some of its reactions

The reaction of carbon suboxide with a number of 2-amino-1,3,4-thiadiazoles has given the corresponding pyrimido[1,2-b]-1,3,4-thiadiazoles     

Integral approximations for molecular orbital theory

The electron repulsion integrals arising in LCAO-MO theory are approximated by replacement of the product of two orbitals on different centers by linear combinations of one-center products. The approximation differs from those previously proposed in that the coefficients of the various terms are determined by requiring agreement for certain integrals, and in the emphasis of the role of symmetry in selecting the one-center products. For two-center integrals, the new approximation is significantly better than older approximate methods. Reasons are given for expecting this improvement to extend also to multi-center integrals.

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Zusammenfassung Es wird ein Verfahren zur näherungsweisen Berechnung von Elektronenwechselwirkungsintegralen der LCAO-MO-Theorie beschrieben, bei welchem das Produkt zweier Zustandsfunktionen an verschiedenen Zentren durch eine Linearkombination von Produkten am gleichen Zentrum ersetzt wird. Der Unterschied zu ähnlichen Ansätzen liegt in der Justierung der Koeffizienten. Für Zweizentrenintegrale liefert die hier vorgeschlagene Methode bedeutend bessere Ergebnisse als das Mulliken-Verfahren.

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Résumé Les intégrales de répulsion électroniques intervenant dans la théorie LCAO MO sont calculées d'une manière approchée en remplaçant le produit de deux orbitales sur des centres différents par des combinaisons linéaires de produits à un centre. Cette approximation diffère de celles proposées auparavant par la détermination des coefficients des différents termes au moyen de l'ajustement de certaines intégrales et par l'importance du rôle de la symétrie dans le choix des produits monocentriques. Cette nouvelle approximation est bien meilleure que les anciennes en ce qui concerne les intégrales bi-centriques. Nous donnons des raisons d'espérer que cette amélioration s'étendra aux intégrales polycentriques.

     

Ab initio MO-SCF calculation on a model of anomalous water

Ab initio calculations are carried out on the planar hexamer model of anomalous water using a variety of basis sets. The results are compared to results of similar calculations on free water and water in the ice I-like puckered ring configurations.

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Zusammenfassung Es werden ab initio-Rechnungen für das planare Hexamer-Modell von anomalem Wasser unter Verwendung mehrerer BasissÄtze durchgeführt. Die Ergebnisse werden mit Resultaten Ähnlicher Rechnungen über freies Wasser und Wasser in der I-Eis Ähnlichen Konfiguration verzerrter Ringe verglichen.

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Résumé Calculs ab initio sur le modèle hexamérique plan de l'eau anormale en utilisant différentes bases. Les résultats sont comparés à ceux de calculs similaires sur l'eau libre et sur l'eau dans une configuration cyclique compacte analogue à celle de la glace I.

     

Structure and conformational isomerism of the major dimer of 2,3-naphthoquinodimethane

The major product from 2,3-naphthoquinodimethane formed by cyclisation of $\text{o}$-dipropadienylbenzene was found to be the dimer 5 containing an eight-membered ring, for which the inversion barrier was determined by dynamic ¹H NMR spectrometry, ΔG3 = 18 kcal/mole.     

Unusual dealkylations and rearrangements in aromatic nucleophilic substitution

The reaction of 2,4-dinitrohalobenzenes with di-isopropylamine produces mainly N-(2,4-dinitrophenyl)-isopropylamine and N-(2,4-dinitrophenyl)-n-propylamine instead of the expected straightforward substitution product. Dealkylations are also observed in the reactions with isopropylcyclohexylamine and dicyclohexylamine. A carbanionic mechanism is proposed.     

Rearrangements of organometallic compounds : XVII. Synthesis of lactones via the titanium-catalyzed hydromagnesiation of alkenols

An efficient, two-step synthesis is presented for preparing γ- and δ-lactones from aldehydes or ketones. (1) the addition of vinyl- or allyl-Grignard reagents to the appropriate carbonyl substrate; and (2) the titanium-catalyzed hydromagnesiation of the resulting alkenols with ethyl Grignard reagent and (η⁵-C₅H₅)₂TiCl₂, followed by carbonation. The selectivity of hydrometallation observed with 3-butenyl(methyl)vinylcarbinol indicates the importance of alkoxytitanium hydrides in determining the course of reaction.     

Distribution of polymer deposition in plasma polymerization. III. Effect of discharge power

Distribution of polymer deposition in an inductively coupled rf discharge system is studied as a function of level of discharge power with acetylene and styrene as monomers. When a fixed flow rate is used, the discharge power has a relatively small effect on the pattern of distribution of polymer deposition as long as values of W/FM, where W is discharge wattage, F is flow rate, and M is molecular weight of monomer, are maintained above a critical level to maintain full glow in the reaction tube. It has been shown that plasma polymerization of two monomers which have different molecular weights can be compared in a fair manner by selecting conditions to yield similar value of W/FM.