Microstructure et détermination des ramifications alkyle dans une série de copolymères éthylène acétate de vinyle

Compounds suitable as models for copolymers of ethylene with vinyl acetate have been prepared and studied by ¹³C-NMR (62.89 MHz). By mixing model compounds, various branched copolymers were simulated. The results have permitted an assignment more complete than previously reported for these copolymers. An investigation was made on the number of branches in nine separate copolymers. The number of ethyl, butyl, pentyl and longer branches per 1000 carbons in the main chain were determined. The number of ethyl branches was around four branches per 1000 carbons; the number of branches longer than butyl decreased from about 20 to 8 per 1000 carbons with increase in vinyl acetate content; the butyl branches predominated over those of other types when the vinyl acetate content was ⩽25% by weight.     

Etude par spectroscopie Raman de la liaison hydrogène dans l'éthylènediamine à l'état solide sous ses deux formes allotropiques

The Raman spectra of partially deuterated ethylenediamine (5 and 95% on NH₂ groups) have been recorded between − 46 and − 196°C in the region of the NH and ND stretching vibrations. The vibrational frequencies of the isotopically diluted NH and ND bonds enabled us to demonstrate the importance of the hydrogen bonds in the cohesion of the crystals and during the allotropic transformation, and also to show the influence of the asymmetric effect on the form of the normal modes of vibration of the NH₂ groups.     

Synthèse de polymères du polyéthylène et du polypropylène à greffons fluorés

Synthesis of fluorinated graft polymers was carried out by two methods. In the first, we use a macromolecular initiator to start the polymerization of a fluorinated monomer in solution, emulsion or in bulk; graft copolymers containing up to 30% of fluorinated grafts were prepared. The second method consists in the condensation of a functional oligomer on a functional graft copolymer. This method was very efficient leading to a new series of graft copolymers with 40% of fluorinated chains.     

Greffage de modèles de lignines sur polystyrène par lien imino

The synthesis of oligolignols grafted on polymer (LFP) was engaged in order to further study the properties and the biodegradation mechanisms of the different lignin sub-units in conditions more similar to those involved in the natural polymer. Simplified lignin models were grafted by an imine or amino link to a 1 % amino ethyl polystyrene resin without any protection of the hydroxyl functions. Infrared was used to characterize the supported models. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASsupported lignine / synthesis / lignin models     

Modélisation de la durée des sons dans un système de reconnaissance automatique de la parole

A major deficiency of standard Hidden Markov Models (HMM) is that both the spectral and the prosodic features are uniformly processed. To combine more efficiently the prosodic cues with the acoustic ones, a segmental Two Level HMM has been recently studied by Suaudeau. In this paper, we present an adapted version in which the segmental processing is replaced by the classical centisecond one, and the prosodic feature is the sound duration. Experiments on a French database show that such an explicit introduction of prosodic parameters reduces recognition error rates.     

Etude du phénomène de dépiégeage des ondes de densité de charge dans les systèmes de basse dimensionnalité

Numerical results of the behaviour of a low dimensional system show that the electric resistivity depends on the friction coefficient generated by the defects. We also show that the electric field dependence of the response time at different friction coefficients follows a power law. The divergence of the charge density wave response time near the threshold field indicates that depinning may be viewed as a dynamical critical phenomenon.     

Réactivité des macromonomères styréniques du polyoxyéthylène en transfert radicalaire

During the homo- and copolymerization with butyl acrylate of styrenic macromers of polyoxyethylene, the molecular weight of the polymer is found to increase continuously because of transfer to the polymer. The polymerization of butyl acrylate in the presence of non-polymerizable model compounds of the macromers has been studied. It is shown that the transfer involves chiefly the benzylic protons; the transfer constant is 2.1 × 10^–3, i.e. larger than that corresponding to the ethylene oxide moiety, which is about 3 × 10⁻⁴. A kinetic study shows that the efficiency of the transfer radicals for reinitiation is about 0.75.     

Mise en evidence des vibrations de la liaison CH dans des motifs structuraux de type alkylidène cyclopropane

The CH bond vibrations in alkylidene cyclopropanic compounds

have been assigned according to experimental results based on vibration—rotation structures, Raman depolarisation ratios, isotopic substitution and solvent effects. They are found at: 3072-3050cm⁻¹ (vCH), 1100-1050 cm⁻¹ (δCH) and 736-700 cm⁻¹ (γCH).     

Une nouvelle méthode de dosage colorimétrique de l'oxygène dissous dans l'eau

Résumé Nous avons présenté une nouvelle méthode de dosage colorimétrique de l'oxygène dissous dans l'eau. Cette méthode est basée sur la réaction de la solution décolorée de manganèse-formaldoxime. La réduction de la solution du dérivé manganique de la formaldoxime est exécutée avec succès à l'aide de la poudre de zinc. Les appareils peuvent être construits facilement et tous les réactifs nécessaires sont d'usage courant. La coloration est stable et les matières comme nitrate, nitrite, fer ferreux, matières organiques etc. ne font pas obstacle dans cette méthode.

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Summary A new method is given for the determination of oxygen dissolved in water. This colorimetric method uses the decolorized solution of manganeseformaldoxime. The reduction of the solution of the manganic derivative of formaldoxime is successfully accomplished by means of zinc powder. The apparatus is easily constructed and all the needed reagents are readily available. The color is stable and no interference arises because of the presence of such materials as nitrate, nitrite, iron (II), organic matter, etc.

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Zusammenfassung Eine neue Methode der kolorimetrischen Bestimmung von in Wasser gelöstem Sauerstoff wird angegeben. Sie beruht auf der Reaktion einer entfärbten Lösung von Mangan(I)-Formaldoxim mit Sauerstoff. Die Reduktion einer Mangan(II)-Formaldoxim-Lösung läßt sich mit Hilfe von Zinkpulver gut durchführen. Der dazu nötige Apparat ist leicht herstellbar, die dazu erforderlichen Reagenzien von üblicher Qualität. Die bei der Reaktion entstehende Färbung ist stabil. Nitrat, Nitrit, zweiwertiges Eisen, organische Substanzen usw. stören die Methode nicht.

     

Conditions de la condensation de Knoevenagel–Cope pour la synthèse de cétones α,β-éthyléniques

The Knoevenagel–Cope condensation between acetophenone and ethyl cyanoacetate mainly gives 2-cyano-3-phenyl-but-2-enoic acid ethyl ester and a substituted dihydropyridone as a secondary product. We show that this secondary product arises from a ketolisation reaction of acetophenone. As a consequence, we describe a new convenient way to prepare some α,β-insaturated ketones by using the Knoevenagel–Cope reaction conditions.     

Utilisation de matériaux à base d’argiles modifiées dans la conversion du toluène

Clay materials, montmorillonite from Maghniya deposits (Algeria), were used as an acidic catalyst in toluene conversion. Toluene disproportionation reaction in gaseous phase was used. These clays were modified by ion exchange with uranyl ions UO₂²⁺. The surface acidity of catalysts was determined by the stepwise desorption technique (STD) of probe molecules using butylamine and ammonia. Thus, total acidity and distribution of the acidity strength were determined. The results show that materials presented an appreciable total acidity and catalytic activity in studied reaction. The acidity strength of catalysts due to UO₂²⁺ ions was kept at a temperature of 550 °C. A relationship was found between the catalytic activity and acidity strength generated by the introduction of uranyl ions in the clay structure.     

Polymérisation de monomères organiques dans les plasmas froids—4: Étude des structures de polyéthylènes et polytétrafluoroéthylènes,en particulier par résonance paramagnétique électronique

The ethylene and tetrafluoroethylene polymerization in a “cold plasma” leads to polymers with considerable deficiencies of hydrogen or fluorine atoms. With electronic spin resonance, the various kinds of radicals trapped in the macromolecular structure have been detected and in some cases identified and determined. The mechanisms could be partly explained in thermodynamic terms. Irradiation of the corresponding commercial polymers gives some information about degradation processes in the plasma.     

Dérivées des moments dipolaires des liaisons dans le nickel tétracarbonyle et les chrome,molybdène,tungstène hexacarbonyle

Infrared band intensities of Ni(CO)₄ and M(CO)₆ (M = Cr, Mo, W) have been measured. Since the signs of the parameters ∂μ/∂Q_p are known for CO and MC vibrations, the physical solution for each compound is to be chosen among four possible only. The choice is directed by the comparison of the values of the parameters ∂μ/∂R_i for the four compounds. The results point out the molecular character of the parameters ∂μ/∂R_i, mainly for the CO bonds.     

Microdosage colorimétrique de la cystéïne et de la cystine

Thiofluorescein is bleached in alkaline medium by light but reforms its colour on reaction with —SH groups. This can be used for the colorimetric determination of cystine and cysteine in the micromolar range.     

Étude des propriétés viscoélastiques de quelques polyfluorure de vinylidène fondus

The rheological behaviour of molten poly(vinylidene fluoride) was studied in steady flow and dynamic flow. An attempt was made to correlate the experimental results with extrudability.     

Simulation théorique de la torsion par liaison hydrogène de la 2,2-biquinoléine à l'état fondamental

Application of the semi-empirical AMI method gives significant evidence of the conformation of the isolated 2,2′-biquinoline (2,2′-BQ) in its ground state. The results obtained on the one hand by Fraga's method in which the molecule is simulated by the hydrogen bonding between a water molecule and the 2,2′-BQ, and on the other hand by CNDO calculations using Mataga's model, are in good agreement with the experimental results. They indicate that the spectral changes of 2,2′-BQ in its ground state in protonic media are caused by a trans-cis transformation resulting from a rotation around the single CC bond which links the two quinoline rings of the molecule     

Application de la dynamique des solutions concentrées de polymères à la résonance acoustique de réticulation

One can characterize the large-scale displacements of a macromolecule by the time required for the chain to renew completely its conformation. These displacements are displayed by changing the topological orientation of the condensation reactions. This effect is produced by putting the medium through a sound wave or an alternating electric field that is in resonance with the Brownian motion of the macromolecule. The physical contact between the chains is enhanced and the intermolecular reactions are more frequent than the intramolecular reactions. The application of a sound wave or an electric field of a characteristic frequency on the elastomers during chemical crosslinking produces a noticeable change in the crosslinking density.     

Evaluation du fe3+ dans les spinelles pour l'obtention de la fugacité d'oxygène des nodules ultrabasiques

The analysis by electron microprobe allows the evaluation of the quantity of Fe³⁺ in spinels with considerable errors. The use of a correction equation which is based on a the calibration of analyses with an electron microprobe in relation to those carried out with Mössbauer spectroscopy gives more precise evaluations of Fe³⁺. In fact, it allows a calculation of the oxygen fugacity in peridotitic xenoliths. The obtained results show that peridotites of the French Central Massif crystallised under oxygen fugacities which were higher than those of the Moroccan AntiAtlas.