Anionic surfmers in mini-emulsion polymerisation

Mini-emulsion polymerisation of styrene or methylmethacrylate, initiated with ammonium persulphate, have been carried out, in the presence of hexadecane or of polymethylmethacrylate as hydrophobic costabilizer, and the simple hemiester of linear dodecyl alcohol and maleic anhydride, or polymerisable surfactants (surfmers) derived from the condensation of succinic anhydride and either hydroxy propylmethacrylate (MAES), or hydroxyethylmethacrylate (ABS). While the pure surfmers have not so good surface activity, from surface tension measurements, stable mini-emulsion droplets are obtained using a mixture with low amounts of SDS, which have diameters of about 100–200 nm, which remain stable upon polymerisation. Most of the surfmers remain grafted onto the particle surface, thus conferring to these particles strong stability in the various tests. However, due to the high water solubility of the surfmers, another part remains in the serum as unconverted monomer or water-soluble polymers. To cite this article: A. Guyot et al., C.R. Chimie 6 (2003).     

Cosurfactant effects on the microemulsion polymerization of styrene

The polymerization of styrene in o/w microemulsions stabilized with dodecyltrimethylammonium bromide (DTAB) with or without cosurfactant (n-butanol, n-hexanol or n-octanol) is examined here. The addition of a cosurfactant enhances the one-phase region in the order: n-butanol > n-hexanol > n-octanol. The kinetics of polymerization slows down in the presence of the alcohol. With the alcohol, the molar masses increase, but no particular trend was noticed on particle size of the lattices. However, by changing the surfactant counter-ion to chloride, alcohol effects on the kinetics almost vanish. Possible explanations to these results are given here. To cite this article: J.E. Puig et al., C. R. Chimie 6 (2003).     

Enantiopure aryl-[1,2,5,6-tetrahydro-pyridinyl] methanols and their use for heterogeneous hydrogenation of ethyl pyruvate

Both enantiomers of two new chiral modifiers (naphthyl- and anthryl-[1,2,5,6-tetrahydro-pyridinyl] methanols, 4H and 5H) are obtained for the first time from inexpensive d-mannitol in 10 easy steps. Until now erythro-4H is the only synthetic chiral modifier available under both enantiomeric forms, which provide enantioselectivities almost as high as those obtained with natural cinchonidine, for which only one enantiomer is available. It is shown that the anthryl group may be less efficient than the naphthyl (the e.e.% drops from 75% with erythro-4H to 46% with erythro-5H) and that N-methyl substitution (trisubstituted nitrogen as in cinchonidine) leads also to a drop in the e.e.% (from 75% with 4H to 39% with 4Me).     

The effect of first-stage polymer Tg on the morphology and thermomechanical properties of structured polymer latex particles

A series of heterogeneous latexes having stage ratios of 40:60 between the first and second stage polymers were prepared by emulsion polymerization. The first-stage polymers were non-polar S-BuA with T_gs ranging from + 100 °C to + 20 °C and the second stage polymer was polar MMA–BuA–MAA having a T_g of 20 °C. The latex particle morphologies were studied using TEM and the thermomechanical properties of the resulting latex films were studied with DSC and DMA. Calculated diffusion rates for propagating species during the reactions were correlated to the observed morphologies and to the amount of interphase in the latex particles. To cite this article: O.J. Karlsson et al., C. R. Chimie 6 (2003).     

Technetium transmutation and production of artificial stable ruthenium

The recent Russian results on technetium transmutation into ruthenium are summarized, including the first isolation of artificial stable ruthenium from irradiated technetium targets. To cite this article: V. Peretroukhine et al., C. R. Chimie 7 (2004).

Résumé

Transmutation du technétium et production du ruthénium artificiel. Les résultats obtenus en Russie sur la transmutation du technétium en ruthénium artificiel et son isolement des cibles irradiées sont présentés. Pour citer cet article : V. Peretroukhine et al., C. R. Chimie 7 (2004).     

Synthesis and reactivity of new heterodinuclear iron/rhenium Cx complexes of the formula (η-C5Me5)Re(NO)(PPh3)(CC)n(η-dppe)Fe(η-C5Me5) (n = 3, 4): Redox properties and a dicobalt hexacarbonyl adduct

We report in this communication the synthesis and characterization of two Fe/Re heterodinuclear complexes 3_n of formula (η⁵-C₅Me₅)Re(NO)(PPh₃)(CC)_n(η²-dppe)Fe(η⁵-C₅Me₅) (n = 3, 4) as well as the hexacarbonyl dicobalt adduct (4) of the hexatriynediyl complex 3₃. We show by cyclic voltammetry that the “electronic communication” between the organometallic endgroups and thereby the thermodynamic stability of the corresponding mixed-valent (MV) parent 3_n⁺ is strongly influenced by bridge extension or by complexation of the [Co₂(CO)₆] fragment. In the case of the hexatriynediyl complex, the MV complex 3₃⁺ or 4 can be isolated by performing the chemical oxidation of 3₃ at low temperature. Spectroscopic studies of this compound and of other stable oxidized redox congeners should now help us to unravel how bridge extension modifies the electronic communication between the different redox-active endgroups in this family of unsymmetrically-substituted polyynediyl compounds.     

Modeling of reactive systems in twin-screw extrusion: challenges and applications

Reactive extrusion processes involve the difficulties of mastering classical polymer processes, such as twin-screw extrusion for example, and the problems of controlling a chemical reaction in very specific conditions (high-viscosity medium, high temperatures, short residence times). Therefore, it is often very difficult to intuitively understand all the aspects of the process and to clarify the complex interactions between the numerous variables, and then to properly design and optimize the industrial process. Numerical modeling can be a very efficient tool to overcome these difficulties. However, it remains a real challenge, as it necessitates to couple flow simulation in complex geometry, reaction kinetics and evolutionary rheological behavior. Moreover, the information needed is sometimes difficult to obtain with the required accuracy. After a general presentation of the principles of the different reactive extrusion modeling methodologies, we will focus on the models we developed, based on continuum mechanics. Different examples of applications are presented for illustrating the interest of this method. To cite this article: B. Vergnes et al., C. R. Chimie 9 (2006).     

On the optimal surfmer addition profile in emulsion polymerisation

In this work, the optimal surfmer feeding profile for stabilizing a high-solid-content acrylic latex with a non-ionic alkenyl functional ^TMMaxemul 5011 was calculated. For this purpose, the model developed by de la Cal and Asua (J. Polym. Sci., Part A: Polym. Chem. 39 (2001) 585) was used. It was observed that, in spite of the low reactivity of the surfmer, it was possible to increase substantially the surfmer conversion using an optimal surfmer addition policy. To cite this article: E. Aramendia et al., C. R. Chimie 6 (2003).     

Synthesis of polydimethylsiloxane microemulsions by self-catalyzed hydrolysis/condensation of dichlorodimethylsilane

The preparation of PDMS microemulsions was carried out by adding at controlled rate dichlorodimethylsilane (DCMS) in a solution of sodium dodecylpolyoxyethylene(8) sulphate. The instantaneous hydrolysis of DCMS and subsequent condensation of the corresponding dihydroxysilane generate dispersions of cyclosiloxanes of small lengths (4 to 6 D units). The high load of chloride ions released during the hydrolysis step requires the presence of the above-mentioned electrosteric surfactant to avoid rapid coagulation of the dispersion. In addition, its sulphate end-group captures a proton that catalyses the ring-opening polymerization of cyclosiloxane as well as the polycondensation of disilanol PDMS chains. Final particles exhibit a diameter of about 50 nm for a polydispersity index of less than 1.1. They are constituted of PDMS chains exclusively linear ( ; ) and of small cycles in low contents (less than 5 wt% in the best conditions). To cite this article: G. Palaprat, F. Ganachaud, C. R. Chimie 6 (2003).     

Research and application of inorganic selective sorbents at Mayak PA

This work has been performed in order to identify selective inorganic sorbents for caesium and strontium. Thin-layer sorbents with nickel ferrocyanide embedded in an inert matrix were found to be the best for caesium. Sorbents including non-stoichiometric manganese dioxide were selected for strontium. Bench tests have been carried out on the purification of desalted water of SNF storage-pool from ¹³⁷Cs, and on the purification of contaminated natural water from ⁹⁰Sr. The facility for synthesizing the ferrocyanide sorbent with the registered mark ‘Seleks-CFN’ has been brought into operation. The sorbent ISM-S seems promising for ⁹⁰Sr decontamination. To cite this article: M.V. Logunov et al., C. R. Chimie 7 (2004).

Résumé

Recherches et applications sur l’utilisation de sorbants spécifiques à Mayak. Des sorbants sélectifs du césium et du strontium ont été identifiés. Pour le césium, le meilleur s’avère être le ferrocyanure de nickel, s’il est utilisé sous forme de couche mince. Pour le strontium, on a sélectionné des composés non stœchiométriques de dioxyde de manganèse. On a mené des tests visant à épurer en césium l’eau des piscines d’entreposage des combustibles nucléaires usagés, et en strontium des eaux contaminées. Une installation industrielle permettant de préparer le sorbant à base de ferrocyanure de marque « Seleks-CFN » a été réalisée. Le sorbant ISM-S semble prometteur pour la décontamination en strontium. Pour citer cet article : M.V. Logunov et al., C. R. Chimie 7 (2004).     

Hybrid copolymer latexes cross-linked with methacryloxy propyl trimethoxy silane. Film formation and mechanical properties

We describe in this work the copolymerization reaction of 3-trimethoxysilyl propyl methacrylate (MPS) with styrene (Styr.) and n-butyl acrylate (BuA) monomers through emulsion polymerization. The so-produced hybrid copolymer (P(BuA-co-MPS)) and terpolymer (P(Styr-co-BuA-co-MPS)) latexes were cast into films that displayed a good optical transparency. The copolymers microstructure in the films was characterized by FTIR, ¹³C and ²⁹Si solid state NMR spectroscopies, and was found to be highly dependent on parameters such as the monomer feed composition, the suspension pH and the silane addition profile. The films obtained from the hybrid latexes showed improved dynamic mechanical properties indicating that a reinforcing organo-mineral network had formed in the composite materials. The dynamic modulus of the hybrids increased with increasing silane contents while, concurrently, the tan δ peak shifted to higher temperatures, broadened and decreased in intensity. To cite this article: S. Vitry et al., C. R. Chimie 6 (2003).     

Solid-state synthesis of boron subnitride, B6N: myth or reality?

Solid-state synthesis of boron subnitride, B₆N, as a result of chemical interaction between boron and boron nitride at 7.5 GPa and 1700 °C has been previously reported by Hubert et al. However, a critical analysis of the results has shown that the evidence for the formation of boron subnitride with B₆O-like structure is inconclusive. We have studied in situ the interaction between boron and BN at the same p–T conditions using X-ray diffraction with synchrotron radiation. At 7.4 GPa and 1700 °C the formation of a new phase has not been observed. At the same time, HP–HT treatment has resulted in strong and unpredictable preferred orientation of boron crystallites. This leads to the rise of some weak boron reflections that might be erroneously attributed to the appearance of a new phase. To cite this article: V.L. Solozhenko et al., C. R. Chimie 9 (2006).     

Effect of the surfactant concentration on the kinetics of oil in water microemulsion polymerization: a case study with butyl acrylate

A comprehensive investigation of aqueous microemulsion polymerization of butyl acrylate at high surfactant concentrations by means of reaction calorimetry and dynamic light scattering revealed unexpected results with regard to polymerization kinetics and colloidal properties of the final latexes. Particularly, with increasing surfactant concentrations, a decrease in the overall rate of polymerization accompanied by an increasing incubation time of the polymerization and increasing average particle sizes in the final latexes has been observed. Based on reviewing former results on microemulsions and microemulsion polymerizations published in the open literature and the presentation of new experimental results an attempt is made to explain the experimental results consistently with a particle nucleation mechanism based on the classical nucleation theory. To cite this article: K. Tauer et al., C. R. Chimie 6 (2003).     

Lavoisier and meat stock

Antoine-Laurent de Lavoisier published his results on ‘meat stock’ preparation in 1783. Measuring density, he stated that ‘food principles’ were better extracted using a large quantity of water. This result was checked. To cite this article: H. This et al., C. R. Chimie 9 (2006).     

Synthesis and structure of the unsymmetrical β-diimine precursor: The β-iminoamine

The reaction of benzoylacetone with ortho-substituted aniline derivatives gives the unsymmetrical β-iminoamine ligands (5–8) with high yields. A convenient synthesis is described. These compounds have been characterized by NMR and IR spectroscopies. The structure of the β-iminoamine 5, 3-N-(2,6-diisopropylphenylamino)-1-phenyl-1N-(2,6-diisopropylphenylimino)but-2-ene, was solved by X-ray diffraction methods.     

Comparison of H3PW12O40 and H4SiW12O40 heteropolyacids supported on silica by H MAS NMR

The H₃PW₁₂O₄₀ and H₄SiW₁₂O₄₀ heteropolyacids supported on silica were studied by ¹H MAS NMR as a function of both the coverage and the dehydroxylation temperature. The signal at ca. 8 ppm attributed to the highly acidic protons of the anhydrous form of the heteropolyacid was never observed in the case of the phosphotungstic polyanion supported on silica while it was clearly present in the case of the silicotungstic species. These results explain the different activities of the two supported heteropolyacids in acid reactions involving strong acid sites. To cite this article: A. Thomas et al., C. R. Chimie 8 (2005).     

A unique transurf in styrene emulsion polymerization

The surface-active, chain transfer agent (‘transurf’) sodium ω-mercapto-decane sulfonate, SMDSo, was synthesized, purified, and its interfacial properties determined. The compound acted normally in styrene emulsion polymerization to produce extremely stable colloids containing only sulfonate ionic surface functional groups. It was then used to control the surface charge density of a model polystyrene colloid by means of seeded emulsion polymerization. Surface charge could thus be increased 16-fold over that of the seed particles, and was due solely to sulfonate groups introduced by the SMDSo. Unlike most conventional emulsion polymerizations, this technique allows one to control surface chemistry independently of particle size. To cite this article: C.C. Fifield, R.M. Fitch, C. R. Chimie 6 (2003).     

Application of phosphorus- and nitrogen-containing organic compounds for the isolation of actinides and technetium from acid or basic aqueous solutions

The derivatives of ethers of phosphoric acid, namely O-(2-alkyl) (diethylcarbamoylmethyl) phenylphosphinates (O2ADECMPP), were synthesized and tested for liquid–liquid extraction of transuranium elements, lanthanides and technetium in meta-nitrobenzotrifluoride or 1,2-dichlorethane from acidic solutions. The O-(ethylhexyl) (diethylcarbamoylmethyl) phenylphosphinate (O2EHDECMPP) was used to prepare chelating granulated sorbents. The family of chelating fibrous ‘filled’ sorbents POLYORGS-type shows, according to preliminary experiments, that Pu and Tc at concentrations around 10^–5 M can be recovered almost completely. POLYORGS show fast kinetics for sorption processes. To cite this article: G.V. Myasoedova et al., C. R. Chimie 7 (2004).

Résumé

Utilisation de réactifs phosphorés et azotés pour la séparation des actinides et du technétium de milieux acides et basiques. Des dérivés de l’éther de l’acide phosphorique du type O-2-alkyl diéthylcarbamoylméthyl phénylphosphonates ont été préparés et testés pour extraire des éléments transuraniens, des lanthanides et du technétium dans le meta-nitrobenzène ou le 1,2-dichloroéthane, à partir de solutions aqueuses acides. Le dérivé O-éthylhexyl diethylcarbamoylméthyl phénylphosphonate a été utilisé pour préparer des échangeurs solides par effet de chélation. La famille des chélatants fibreux Polyorgs montre, dans des expériences préliminaires, que Pu et Tc, à des concentration de l’ordre de 10^–5 M, peuvent être complètement récupérés à partir de milieux acides contenant d’autres éléments. Ces composés présentent des cinétiques de sorption très rapides. Pour citer cet article : G.V. Myasoedova et al., C. R. Chimie 7 (2004).     

Recent progress in nitroxide-mediated polymerizations in miniemulsion

Recent developments in nitroxide-mediated polymerizations conducted in emulsion and miniemulsion have advanced the field across a range of both experimental and theoretical fronts. This article reviews progress in bicomponent initiating systems (including use of camphorsulfonic acid to enhance rate), unimolecular initiating systems, miniemulsions not requiring the use of volatile costabilizers, polymerization of acrylates, mathematical modeling and simulation, and theoretical understanding with regards to issues such as compartmentalization, preservation of polymer chain livingness, the role of aqueous phase kinetics and phase partitioning. These topics are discussed and analyzed to present an integrated portrait of the current status of nitroxide-mediated polymerizations in emulsion/miniemulsion and to identify the most pressing concerns, issues, and opportunities. To cite this article: M.F. Cunningham, C. R. Chimie 6 (2003).     

Titanate-based ceramics for separated long-lived radionuclides

Studies have been conducted in France to minimize the potential long-term impact of nuclear waste by enhanced chemical separation of the minor actinides (Np, Am, Cm) and some long-lived fission products (I, Cs, Tc). Two options may be considered following this work: (i) the initial reference option is transmutation by neutron bombardment in nuclear facilities, (ii) the second option would be to incorporate the separated elements into an inorganic matrix ensuring long-term stability. In the case of specific conditioning, zirconolite and hollandite are the potential host phases for the minor actinides and caesium, respectively. Both of these matrices have shown strong potential: (i) for incorporating the respective radioelement in the crystalline structure, (ii) for fabricating the ceramic by natural sintering in air, (iii) for chemical durability with a very low initial alteration rate (about 10^–2 g m^–2 d^–1 at 100 °C), then very rapidly reach alteration rates more than four orders of magnitude lower. In the case of zirconolite ceramics, the high chemical durability is conserved even after amorphization of the crystalline structure by external irradiation with heavy ions or by self-irradiation in natural zirconolites 550 million years old. To cite this article: C. Fillet et al., C. R. Chimie 7 (2004).

Résumé

Pour réduire l'impact potentiel à long terme des déchets nucléaires, des études sont conduites en France sur la séparation chimique poussée des actinides mineurs (Np, Am, Cm) et de certains produits de fission à vie longue (I, Cs, Tc). À l'issue de cette étape, deux options sont envisageables : (i) la transmutation par bombardement neutronique dans des systèmes nucléaires est la première option de référence, (ii) la seconde option consisterait à incorporer les éléments séparés des autres déchets nucléaires dans une matrice minérale stable à long terme. Dans le cadre d'un conditionnement spécifique, la zirconolite et la hollandite sont des phases hôtes potentielles respectivement pour les actinides mineurs et le césium. Ces deux matrices ont montré une potentialité élevée (i) d'incorporation du radioélément considéré dans la structure cristalline, (ii) d'élaboration de la céramique par des procédés de frittage naturel sous air, (iii) de durabilité chimique, avec une vitesse initiale d'altération très faible (de l'ordre de 10^–2 g m^–2 j^–1 à 100 °C), puis très rapidement des diminutions des vitesses d'altération de plus de quatre ordres de grandeur. Pour la céramique zirconolite, cette propriété de durabilité chimique élevée reste conservée, même après amorphisation de la structure cristalline par irradiation externe aux ions lourds ou par auto-irradiation sur des zirconolite naturelles âgées de 550 millions d'années. Pour citer cet article : C. Fillet et al., C. R. Chimie 7 (2004).