Processus de photopolymerisation du methacrylate de methyle en presence de chlorure de zinc

The photopolymerization of methylmethacrylate in solution or in bulk, initiated by DMPA (2,2-dimethoxy-2-phenylacetophenone) and BP (benzophenone), has been investigated in the presence of ZnCI₂ as a complexing agent. We have studied the steady state polymerization (measurement of R, and OT) and the behaviour of the excited states by laser spectroscopy. We have shown the following points: R_p and DP increase with [ZnCI₂]; the rate constant for propagation increases with [ZnC12]; the rate of initiation remains constant in presence of BP-ZnCl₂ but increases with DMPA-ZnCl₂. The results are accounted for by the results of laser spectroscopy.     

Etude de la fragmentation de derives de L'uracile et de la thymine par Spectrometrie de masse

Original mass spectra of uracil and thymine derivatives are presented with the corresponding fragmentation schemes. In the first series of spectra, the fragmentations of thymine derivatives, including ¹⁴C-2-thymine, dimers, and bromo thymines, confirm the basic retro Diels-Alder mechanism. The second series includes dihydro 5,6-derivatives of uracil (hydroxy and bromo substituents). The behaviour of these molecules is quite different; they are more sensitive to the substituents and a part of the fragmentation is often explained by protonated molecular ions.     

Synthese de polyacrylamides porteurs de groupements iminodiacetate et etude de leur pouvoir de complexation vis-a-vis de quelques cations metalliques

Water soluble polymers were prepared by topochemical reaction of sodium iminodiacetate with polymethylolacrylamide. Their complexing properties towards some metallic cations were investigated by potentiometric and spectroscopic techniques and compared with the complexing properties of iminodiacetic acid and of a model molecule of the polymer ionic unit. The results showed that polymer and model 1-1 chelates are stronger than iminodiacetic complexes. We explain this difference by participation of the amide group in the coordination of cation by the two first ligands.     

Elaboration de capteurs de gaz a partir de ceramiques conductrices ioniques de type NaSICON

The elaboration of Na⁺ super-ionic conductor (NaSICON) ceramics is studied in this work. These solid electrolytes can be used as sensor for detection of polluted gases in air. Two sorts of ceramics with different chemical compositions are synthesised by soft chemistry route: a zirconium-based NaSICON and a hafnium-based NaSICON. DTA-TG and temperature depending X-ray diffractometry were used to follow the thermal decomposition of the precursor phases. The electrical properties of these ceramic sodium ionic conductors are investigated by complex impedance spectroscopy (CIS). The substitution of the zirconium by the hafnium increases the ceramic conductivity and decreases the activation energy E ^a (from 0.29 to 0.12 eV). This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthese regioselective de bases de mannich de cetones dissymetriques

Methods for the regioselective synthesis of Mannich bases starting from unsymmetrical ketones are described. The Mannich base on the more substituted carbon is obtained by reaction with (CH₃)₂N⁺CH₂,CF₃CO₂^- in CF₃CO₂H and its isomer on the less substituted carbon with (iPr)₂N⁺CH₂,ClO₄^- in CH₃CN. In the first case, the orientation corresponds to a non-selective attack of the immonium salt on a mixture of enols in which the more-substituted isomer is predominant. In the second ease, use of a bulky immonium salt induces a selectivity favoring the less-substituted enol.     

Modification chimique de polyisoprenes et de polybutadienes de faible masse par addition de trichlorosilane

The addition of trichlorosilane to carbon-carbon double bonds of low molecular weight polyisoprenes and polybutadienes has been studied with hexachloroplatinic acid as catalyst. The reaction was carried out in benzene as solvent, at 110, under nitrogen pressure. The reaction rate decreases as the carbon-carbon double bond substitution increases. In most cases, addition of trichlorosilane is accompanied by cyclization reactions more or less important depending on the polymer structure, except for 1,2-polybutadiene. Trichlororosilyl groups have been modified to trimethyl and trimethoxy derivatives.     

Cinetique de polymerisation de monomeres complexes par des acides de Lewis. Etude du systeme methacrylate de methyl-chlorure de zinc-azobisisobutyronitrile

The polymerisation of methyl methacrylate (MMA) initiated by azo-bis-isobutyronitrile (AIBN) in the presence of ZnCl₂ as complexing agent has been investigated. Increase of the polymerisation rate and a minimum in the average polymerisation degree were observed by increasing the ZnCl₂ concentration. By assuming the existence of complexes {AIBN · ZnCl₂} and {MMA · ZnCl₂}, a kinetic scheme is proposed; it is in good agreement with the experimental results and allows calculation of the characteristics of the system.     

Quelques caracteristiques morphologiques de melanges de polymeres a base de propene et de butene

This paper reports a study of the morphology of blends of polypropene with polybutene as a function of composition. Techniques such as differential thermal analysis, thermomechanical analysis and dilatometry were used. The “compatibility” of these polyolefines is considered. Glass transition temperatures of the homopolymers are detectable when using the various techniques.     

Etude de la chloration du polychlorure de vinyle en fonction de sa tacticite

Polyvinyl chloride samples of various tacticity have been prepared and photochlorinated in CCl₄ for 4 hr. The chlorination degree correlates directly with the degree of syndiotacticity. Initial PVC with syndiotacticity about 56 per cent, which can be regarded as alternate sequences of syndiotactic and isotactic diads, is quickly chlorinated. The mechanism of chlorine attack on the macromolecula is directly connected with the stereoregularity.     

Analyse destructive de traces de rubidium dans des echantillons mineralogiques par radioactivation au moyen de neutrons de 14 MeV

Increasing interest is devoted in geochemistry to the determination of minor elements in rocks and minerals with the best analytical precision. The use of different methods is quite useful to point out and overcome the systematic and specific interferences of the geological matrix. 14 MeV neutron activation analysis can be used for such a purpose as an additional check method. A successful attempt has been made in the determination of rubidium in different geochemical standards. A sensitivity of 100 ppm can be reached with a 5% precision without any interference problem.     

Preparation et caracterisation de reticulats-modele de polydimethylsiloxanes

Three-dimensional crosslinked gels of polydimethylsiloxanes with well-defined pore-size have been obtained by reaction of the Si-H endgroups with a polyfunctional allyloxy compound. The swelling behaviour of such gels has been investigated. The variation of the swelling degree at equilibrium with the structure of the gel was found in good agreement with the theoretical expectation.     

Conditions de traitement thermique de l'alliage de titane ta6v sous faisceau laser co2 de puissance

Titanium alloys and particularly TA6V are much used in the domain of the aerospace industry and also of chemical engeneering. The thermal treatment by laser of these alloys helps for the improvement of their physico-chemical properties.The laser energy is transformed on the surface of the metallic specimen to thermal energy or heat; this heat diffuses to the interior of the specimen. The microstructure obtained after the laser treatment are metastable ones obtained by quenching out-of equilibrium microstructures; this is due in the case of the laser treatment to the fact that the heating time is a fraction of a second and the cooling rate is very high, in the order of 10³K/s. The microstructures obtained are fine with interesting physico-chemical properties.Considering the strong reaction of titanium with O₂ and N₂, and in order to avoid modifying the resulting microstructure on the surface, a protection against environment during the thermal treatment by laser is required. Blowing argon on the specimens, during the laser treatment results in contaminated materials. The protection against environment is satisfactory when the specimens are treated in a box of Plexiglas filled with argon.     

Synthese de bases de mannich acetyleniques cycliques

Terminal acetylenes can be converted in excellent yields into Mannich bases by reacting them with gem-aminoethers instead of formaldehyde and a secondary amine. This provides a possibility of preparing cyclic aminoacetylenes from w-acetylenic secondary amines, via the derived gem-aminoethers, using high dilution technique.     

Spectres de vibration de pigments rouges de la famille des quinacridones

The i.r. and Raman spectra of various crystalline phases of the trans linear quinacridone and some methylated and chlorinated derivatives have been investigated between 4000 and 200 cm⁻¹. Each of these pigments has been characterized spectroscopically and an assignment for intramolecular fundamentals is given in terms of group frequencies. The strength and length of NH ⋯ O hydrogen bonds have been assessed from the vNH frequency and correlated with the pigment colour which is principally determined by intermolecular interactions rather than by the substituent hypso(batho)chromic effect. The NH ⋯ O distance increases from 2.87 Å for the red compounds to 2.93 Å for the purple ones.     

Evolution des rejets saumatres des stations de dessalement de l'eau de mer au cours de leur evaporation isotherme

Desalination of sea-water was investigated. Effluent of desalination plant was evaporated in isotherm and isobar condition. Density, electric conductivity measurements and chemical analysis were carried out during the process. The results characterising the crystalline phase provide the fields and limits of the precipitation and separation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthese de nouveaux oxydes de tetraphosphines macrocycliques

The direct cycloadditions of two dioxophosphidure dianons with two molecules of an unsaturated dihalide produce unsaturated macrocyclic phosphine tetraoxides that are alkylated on phosphorus. Their reduction by molecular hydrogen is highly selective: the saturated homologues are obtained in excellent yield.     

Etude de la Fragmentation en Spectrographie de Masse de Spiropyrannes Benzodithioliques. Influence de la Position et de la Nature des Substituants

The mass spectra of 12 benzodithiolic spiropyrans are reported. Their fragmentation pathways have been determined by exact mass and metastable transition measurements. The nature of the fragmentation is strongly dependent upon the position and nature of the substituents. A comparison is made with their photo and thermochemical decompositions.     

Etude de la reaction de condensation de systeme epoxyde-amine par resonance magnetique nucleaire - synthese de modeles epoxy-amine

This work is an approach to the analysis, by nuclear magnetic resonance of carbon 13, of epoxy-aminated reticulates in the case of aliphatic aminated hardeners: butylamine, ethylene-diamine, diethylenetriamine, triethylenetetramine. In order to characterize the various species formed at each stage of the reaction, and for various types of resin/hardener stoechiometry, the DGEBA (diglycidyl ether of bisphenol A)/polyamine couple has been modeled by characterizing the structures generated during the reactions of phenylglycidylether (PGE) with two aliphatic amines: n-butylamine (BA) and ethylenediamine (EDA). This study deals with the characterization of non-catalysed systems only (or at least systems without added catalyst).     

Chromatographie sur couche mince de microparticules de gel de silice

Résumé On décrit la préparation de plaques efficaces pour la chromatographie en couche mince (sans liant), utilisant les pertites particules de gel de silice à présent disponibles (5–40 m). On discute le performances obtenues et les illustre par différentes séparations de mélanges faites tant en chromatographie d'adsorption qu'en chromatographie du type partage avec phases inversées. On discute les paramètres qui contrôlent la migration du solvant et l'élargissement des bandes et montre qu'il n'y a pas une nouvelle méthode révolutionnaire de chromatographie mais le progrès normal d'une technique analytique classique, progrès prévu de longue date [1].

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Thin-layer chromatography with microparticles of silica gel

Summary The preparation of efficient thin-layer plates (binder free) made with the newly available samples of small silica gel particles (5 to 40 m) is described. The performances are discussed and illustrated by various applications to the separation of mixtures by adsorption and reversed phase partition chromatography. The parameters which control solvent migration and band broadening are discussed. It is shown that there is no such revolutionary concept as high performance thin-layer chromatography, but merely the normal advance of a conventional analytical technique following predictions made long ago (1).

     

Comparaison de l''action catalytique de thiols monofonctionnels et de certains thiols bifonctionnels (les mercaptoalcoyl-2 benzimidazoles) sur l''hydrolyse de l''acetate de p-nitrophenyle

Synthesis of bifunctional thiols (2-alkylmercaptobenzimidazoles) and kinetic studies of the catalysis of the hydrolysis of p-nitrophenylacetate by these compounds, and by seven thiols indicates high activity of the 2-mercaptomethylbenzimidazoles in their neutral form, interpreted as the result of nucleophilic catalysis by the thiol function in its neutral state combined with general basic catalysis by the heterocycle.