Thermal investigation of the phase composition of poly(ethylene terephthalate). Analysis of different methods of determination of the degree of crystallinity of partially crystalline substances

The literature data on the degree of crystallinity of non-deformed poly(ethylene terephthalate) measured at various temperatures have been subjected to comparative analysis. There is no correlation between the results obtained by the different methods. The reason for this is shown to be the imperfections in the methods of determining the degree of crystallinity, which do not provide the true composition of the crystalline phase. Consideration has been paid to the validity of the main principles involved in the thermal method of determining the degree of crystallinity, so as to eliminate the imperfections in the existing methods and to provide the correct value of the mass of the crystalline phase. The phase composition of PET has been analyzed by the thermal method at different temperatures and conditions of crystallization. A marked difference from the literature data is observed in the range of low temperatures.

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Zusammenfassung Eine vergleichende Analyse der Literaturangaben bezüglich des bei verschiedenen Temperaturen gemessenen Kristallisationsgrades von nicht-deformiertem Poly(äthylen-terephthalat) wurde durchgeführt. Zwischen den mit verschiedenen Methoden erhaltenen Ergebnissen besteht keine Korrelation. Es wurde gezeigt, daß der Grund hierfür in der Unvollkommenheit der Methoden zur Bestimmung des Kristallisationsgrades liegt, da diese nicht die wahre Zusammensetzung der Kristallinen Phase angeben. Die Gültigkeit der wichtigsten Prinzipien, welche die thermische Bestimmung des Kristallisationsgrades unter Ausschaltung der Unvollkommenheit der bestehenden Methoden gewährleisten und den richtigen Wert der Masse der kristallinen Phase angeben, wurden in Erwägung gezogen. Die Analyse der Phasenzusammensetzung von PET wurde durch die thermische Methode bei verschiedenen Temperaturen und Kristallisationsbedingungen durchgeführt. Ein deutlicher Unterschied zu den Literaturangaben kann im Bereich der niedrigen Temperaturen beobachtet werden.

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. , , . , , . , , . . .

     

间位基团激发态取代基常数的扩展及应用

合成了七个系列含间位取代基X的二苯乙烯m-XArCH=CHArY-p(简称m-XSBY-p),其中X为NO_2、I、CHCH_2、Ph、Et、NMe_2和CCH。在无水乙醇中测定它们的紫外(UV)吸收光谱,得到紫外吸收最大波长λ_(max)(nm)。对λ_(max)的波数ν_(max)(cm~(-1))进行定量相关,采用曲线拟合方法,得到上述7个间位基团的激发态取代基常数σ_(CC(m))~(ex)。将对位基团和间位基团的σ_(CC)~(ex)与Hammett常数σ进行对比,表明σx_(CC)~(ex)与σ分别表达取代基不同的电子效应。另外,合成了含上述间位基团的二芳基希夫碱(10个)和二苯乙烯(14个),用所得σ_(CC(m))~(ex)预测它们的λ_(max),并用实验测定它们的λ_(max),结果表明预测值与实验值相吻合,验证了所得σ_(CC(m))~(ex)常数的可靠性。收集了225个化合物(涉及二取代苯及二苯乙烯)的ν_(max),建立了一个统一的定量方程来表达这些化合物ν_(max)的变化规律。     

Influence of thermal activation of chalcopyrite on activity and selectivity of catalytic decomposition of isopropyl alcohol

The decomposition of isopropyl alcohol on natural chalcopyrite was studied by the microcatalytic pulse method in the region 473–673 K. The activity and selectivity of the catalyst was confronted with the temperature of its thermal activation. The apparent activation energies of decomposition were calculated for chalcopyrite activated in argon atmosphere at temperatures of 673, 773, and 873 K. The values of activation energy thus obtained are 61, 38, and 44 kJ mol^–1 The liberation of sulfur from the lattice of chalcopyrite caused by thermal activation gives preference to dehydration over dehydrogenation at lower temperatures. The proportion of hydrogen and acetone in reaction products increases with temperature.

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473–673 . , 673, 773 873 , 61, 38 44 /, . . .

     

Observation of textures of nematic polymers and estimation of the elastic constants

The texture of a copolyesteramide, Vectra® B950, has been studied by optical microscopy. At rest, the defects are typical of a biaxial nematic phase, but under the influence of a magnetic field or under shear, the nematic transforms into a uniaxial phase. The Freedericksz geometry yields a K₁ elastic constant of the order of 10^-8 N. The diffusivities K_III/_n and K_II/_n are obtained by measuring the light intensity transmitted through a sample during shear start-up and relaxation, and from this we estimate K_III ≅ 10 ^-9N and K_II ≅ 10 ^-10N. Since the biaxiality is small, these uniaxial constants adequately describe the phase at rest.     

Discrimination of the mechanisms of cooxidation of arylalkanes and alkylamines

Numerical analysis of experimental data on the cooxidation of arylalkanes and alkylamines indicates a chain propagation and interruption mechanism with the participation of amine cation radicals. The steps corresponding to the classical cooxidation mechanism are excessive in this experiment.

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. , , .

     

Kinetics of perborate oxidation of quinol

The perborate oxidation of quinol in aqueous acetic acid is first order with respect to perborate, zero order with respect to quinol, and first order with respect to H⁺. The oxidation is faster than H₂O₂ oxidation. Breakdown of protonated perboric acid is suggested as the rate-limiting step.

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, H⁺. . , , , .

     

Determination of heats of formation of praseodymium antimonides

A systematic investigation of the heats of formation in the Pr-Sb system has been performed using a small-furnace, isoperibolic calorimeter. The compositions and the equilibrium states of the samples have been checked by metallographic and X-ray analyses. The following values have been found for the various compounds (kJ/g atom±2): Pr₂Sb:-99; Pr₅Sb₃:-112; Pr₄Sb₃:-120; PrSb:-126; PrSb₂:-97.The data available (both the results obtained in this work and those already known) are discussed briefly and related to the possible shape of the phase diagram.

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Zusammenfassung Es wurde eine systematische Untersuchung der Bildungswärmen im Pr/Sb-System unter Verwendung eines Kleinofen-Isoperibolkalorimeters ausgeführt. Die Zusammensetzung und der Gleichgewichtszustand der Proben wurden durch metallographische und röntgenographische Analyse ermittelt. Für die einzelnen Verbindungen wurden folgende Werte (kJ·mol^–1 ±2.0) gefunden: Pr₂Sb:-99; Pr₅Sb₃:-112; Pr₄Sb₃:-120;PrSb:-126; PrSb₂:-97. Die als Ergebnis dieser Arbeit erhaltenen und aus der Literatur bereits bekannte Daten werden kurz diskutiert und mit einem möglichen Phasendiagramm in Verbindung gebracht.

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-Sb, . . ( (-)^–1 ±2.0): Pr₂Sb-99; Pr₅Sb₃-112; PrSb₃-120; PrSb-126; PrSb₂-97. .

     

Reactivity and electronic property of decaphenylmetallocenes of Mo and W atoms

The perphenylmetallocene complexes (η⁵-C₅Ph₅)₂W (1), [(η⁵-C₅Ph₅)₂W]⁺I₃⁻ (1⁺I₃), (η⁵-C₅Ph₅)₂Mo (2) and [(η⁵-C₅Ph₅)₂Mo]⁺I₃⁻ (2⁺I₃) have been prepared. Hydrogenation of 1 in THF produces (η⁵-C₅Ph₅)₂WH₂ (4), while (η⁵-C₅Ph₅)₂WHCl (3) is afforded in 1,2-dichloroethane solvent. Carbonylation of 1 produces (η⁵-C₅Ph₅)₂W(CO) (5). Treatment of 1 with the strong acid CF₃SO₃H leads to the dicationic species [(η⁵-C₅Ph₅)₂W]⁺²[CF₃SO₃]⁻₂ (1⁺²Tf₂) after crystallization. The structures of 2⁺I₃ and 1⁺²Tf₂ have been determined by an X-ray diffraction study. The magnetic susceptibility study indicates a ³E_2g ground-state for 1 and 2, and a ⁴A_2g ground-state for 1⁺ and 2⁺.     

Size- and surface-dependence of enthalpy of oxidation of submicronic magnetites

Submicronic magnetites prepared by two different methods were studied between 30 and 280°, using a fluxmetric microcalorimeter to investigate the size- and surface-dependence ofH, the enthalpy of oxidation of magnetite to-Fe₂O₃.For the particles with mean diameters ranging from 95 to 950 Å and specific surfaces of the order of 100.0 to 10.0 m²/g,H varied from –77.3±2.5 to –61.0±2.5 kJ/mol, and is identified as a linear function of the size of the particles, as depicted by the relationshipH=H _intrinsic+H _D, whereH _D represents the particle size-dependent part of the enthalpy of oxidation.

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Zusammenfassung Nach zwei verschiedenen Methoden hergestellte, submikrone Magnetite werden zwischen 30 und 280° mittels eines fluxometrischen Mikrokalorimeters untersucht, um die Abhängigkeit der EnthalpieH der Oxydation von Magnetit zu-Fe₂O₃ von der Partikelgröße und -Oberfläche zu ermitteln. Für Partikel mit mittleren Durchmessern im Bereich von 95 Å bis 950 Å bzw. spezifischen Oberflächen in der Größenordnung von 100-10 m²/g variieren dieH-Werte von –77,3 ±2,5 kJ/mol bis –61,0±2,5 kJ/mol. Die Enthalpie korreliert linear mit der Partikelgröße, was durch die BeziehungH=H _intrinsic+H _D ausgedrückt werden kann, worinH _D den von der Partikelgröß e abhängigen Teil der Oxydationsenthalpie repräsentiert.

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, , 30–280° H , Fe₂O₃. 95 950 Å , , 100,0 10,0 ²/r, H –77,3±2,5 –61,0±2,5 /. H H=H +H , H — , .

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Paper presented at the World Conference on Thermal Analysis, Madeira (Portugal), 1986.     

Explanation of Theoretical Mechanism of Isomerization of L-Alanine Conformation for Experimental Results

B3LYP/6-31＋＋G＊＊ method was applied to investigate the mechanism of alanine isomerization.12 minima and 22 transition states were obtained after optimization and several paths of isomerization were found.It is found that intramolecular single-bond rotation and proton transfer might lead to isomerization.The energy barrier of C–N bond rotation was lower than 2.52 kcal·mol 1,while the energy barrier ranges of the rotation of C–C and C–O were separately 0.43~ 7.01 and 4.69~12.19 kcal·mol 1,and the minimum energy barrier of proton transfer was 30.76 kcal·mol 1.The most probable isomerization path and mechanism for the two most stable conformations was discussed to find that the highest energy barrier to be crossed in this path was 11.87 kcal·mol 1.In order to understand the microscopic nature why only 4 conformations were detected in the experiment,thermodynamic properties of all conformations at the experimental temperature of 391 K was calculated.It is found that conformations XII,XI,X and IX can only unidirectionally convert into conformations rapidly with low energy and vanish immediately.The other conformations were distributed according to Maxwell-Boltzman＇s law,and the distribution probabilities of conformations I,II,III,IV,V,VI,VII and VIII were respectively 27.2%,26.5%,25.8%,6.4%,5.2%,4.8%,2.5% and 1.6%.Conformations I,II and III with bigger probability and stronger absorption peak were easy to detect in the experiment.Conformation IV had a relatively smaller probability（6.4%） and weak absorption peak which,however,could also be identified.The other conformations had too small probability to identify in the spectrum.     

Nature of extended defects of CuO

For the first time, using high-resolution electron microscopy, extended defects (twins, screw dislocations and microdistortions) of disperse CuO have been found. Their structure is described.

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CuO -, .

     

The measurement of heats of mixing of polymer alloys by a heat of solution method

Direct measurement of the heat of mixing (interaction) of polymers is not feasible due to their high viscosity. The indirect approach described here is a heat of solution method, in which a Hess's Law cycle is used to determine the heat of mixing from the individual heats of solution of the alloy and its constituent polymers in a common solvent. The main limitation of this approach lies in obtaining adequate precision on the experimentally determined heats of solution, as these are large compared to the calculated heat of mixing.With this method the heat of mixing of a 75/25 (%by wt) poly(dimethyl) phenylene oxide/polystyrene alloy has been determined by Setaram C-80 microcalorimeter as 4.9 + 0.2 Jg^–1. The precision of the method shows an improvement compared with published data.

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Zusammenfassung Die direkte Messung der Mischungswärme (Wechselwirkungswärme) von Polymeren ist wegen ihrer hohen Viskosität nicht möglich. Die hier beschriebene indirekte Vorgehensweise beruht auf der Lösungswärme, wobei ein Hess'scher Kreisprozess verwendet wird, um aus den einzelnen Lösungswärmen der Mischung und der sie aufbauenden individuellen Komponenten im gleichen Lösungsmittel die Mischungswärme zu bestimmen. Die entscheidende methodische Grenze ist die notwendige Genauigkeit bei der Bestimmung der Lösungswärmen, da diese gross gegenüber der berechneten Mischurigswärme sind.Mit dieser Methode wurden die Mischungswärme einer Mischung aus 75% Poly(dimethylphenylenoxid) und 25% Polystyren in einem Mikrokalorimeter Setaram C 80 zu 4.9 +- 0.2 J g^–1 bestimmt. Verglichen mit veröffentlichten Daten ist die Methode genauer.

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() - . , , - . , . -80 — 75 25 %, 4,9 ± 0,2 ·^–1. .

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The permission of the British Petroleum Company plc to publish this paper is gratefully acknowledged. The authors would like to thank Professor Karasz for useful discussions.