Degradations photothermiques de polyethylenes reticules. II.—Action photocatalytique d'oxydes metalliques

The chemical modifications of a cross-linked polyethylene sample submitted to photocatalyzed oxidation have been investigated by infra-red spectrophotometry; the spectral changes are compared with those observed in thermal and photothermal oxidation. Zinc oxides and both titanium oxides (anatase and rutile) behaved similarly as photocatalysts. Under excitation by monochromatic light, initial quantum yields of formation of aliphatic ketones have been determined; their variations with macroscopic parameters (excitation wavelength, light intensity, per cent of the photocatalytic oxide) have been studied. Activation energies of the photocatalytic conversion of polyethylene into ketones have been measured under polychromatic light. Finally, it is shown that the simultaneous addition of a photocatalytic oxide and a quinolinic antioxidant is efficient against the oxidative photodegradation of polyethylene.     

Impregnation du polyterephtalate d'ethylene glycol par des composes terephtaliques-methode statique-methode dynamique

A study was made of the sorption of various terephthalic compounds in samples of ethylene glycol polyterephthalate with various morphologies. A static and a dynamic method of impregnation were employed and compared. The dynamic method can be applied to a study of every system of two phases animated by a uniform relative movement of translation, whereas the static method is more rigorous. Only the amorphous polymer treated with solvent (dioxane) absorbs relatively large quantities of terphthalic compounds at temperatures below the vitreous transition point of the polymer. The absorbed product becomes distributed near the surface of the material, and can be fixed there by thermal treatment subsequent to impregnation. This thermo fixing causes the collapse of the swollen macromolecular structure engendered by the solvent treatment. It is thus possible to modify the surface properties of the polymer.     

Preparation d'oxydes de linalol par bioconversion

Microbial cyclisation of linalol(+), (?) and (±) by a nigericin-producing Streptomyces albus gives linalol oxides. Cis linalol oxide gives opposite signs for the rotatory power when measured neat or in solution.     

Etude des solutions solides d'oxyde de lithium dans l'oxyde de nickel. II. Influence de la pression d'oxygene et mecanismes d'incorporation

The formation of solid solutions of lithium and nickel oxides, containing more than 2 at Li %, requires the presence of oxygen under a pressure which must exceed 10^?3 torr at 933 K. Solid solutions containing a maximum of 2 at Li % however can be prepared under a reduced pressure of oxygen (< 10^?4 Torr). Mechanisms are proposed to explain, in both cases, the incorporation of lithium ions in the nickel-oxide lattice.     

Sur la compatibilité des copolymères statistiques binaires et ternaires d'acrylonitrile,d'acétate de vinyle et d'α-méthylstyrène

A comparison has been made between (a) mixtures of the binary copolymers of acrylonitrile with vinyl acetate and with α-methyl styrene and (b) the ternary copolymer. The two products have been characterized for thermal and mechanical behaviour. For each pair of copolymers, a study has been made of compatibility in establishing the type of mixture and the variation of properties with composition.     

Addition d'un polymère “flexible” la polyvinylpyrrolidone à des solutions aqueuses mésomorphes d'un polymère semirigide l'hydroxypropylcellulose

Mesomorphic solutions of a semi-rigid polymer, hydroxypropylcellulose in water, have been studied; the effects of the replacement of a part of the solvent by a flexible polymer, polyvinylpyrrolidone, have also been investigated. The principal effects are (i) lowering of the critical concentration of onset of the anisotropic phase, (ii) raising of the temperature of appearance of the “gel”, (iii) decrease of the pitch of the cholesteric structure. Investigations on different molecular weights of PVP seem to show a modification of the mesomorphic phase in the blend without demixing.     

Mise en evidence de points de transition dans des grains de polyterephtalate d'ethylene par retention de vapeurs

Chromatographic elution analysis was used to study the retention of vapours, in particular methanol, on granular polyethyleneterephthalate. Three transition phenomena of the polymer were revealed between 60 and 250°. Differential thermal analysis allowed further precision in the obtained results. These phenomena were related to structure modification in the polymer.     

Isomerisation thermique d'alkylidenecyclobutanones : Piegeage du diradical intermediaire par migration −1,5 d'hydrogene

The biradical intermediate which results from the thermal ring fission of alkylidene cyclobutanones $\text{2}$ serves as a common precursor of isomerised cyclobutanones $\text{3}$ (1,3 carbon shift), and of dienones $\text{4}$ by way of intramolecular 1,5 hydrogen shift.     

Etude des solutions solides d'oxyde de lithium dans l'oxyde de nickel. I. proprietes des solutions solides preparees sous pression reduite d'oxygene

Heating mixtures of lithium and nickel oxides at 1073°K under reduced oxygen pressure (<10^?6 Torr) produces the incorporation of lithium ions in the nickel-oxide lattice. The solubility appears to be limited at 1.9 at Li %. From a study of several properties of solid solutions, it is concluded that the incorporation of lithium ions creates and stabilizes anionic vacancies.     

Method d'estimation des limites d'inflammabilite

We have employed the criteria defined by the CHETAH (ASTM) program to predict the lower and the upper flammability limits of various organic compounds. The results obtained for molecules containing carbon, hydrogen, oxygen and nitrogen are, in most cases, in good agreement with experimental values. The difficulties encountered when the molecule contains a heteroatom can be overcome by knowledge of the stoichiometric conditions of the combustion reactions.     

Thermal properties of single walled carbon nanotube‐silicone nanocomposites

The effect of single walled carbon nanotube (SWCNT) fillers on the low temperature thermal properties and curing behavior of SWCNT‐silicone nanocomposite are reported for the first time. The SWCNT‐silicone composites were prepared by different mixing procedures and characterized by differential scanning calorimetry (DSC). Solution mix, with the aid of sonication and soaking achieved better dispersion of SWCNTs in the silicone. The adding of SWCNTs in polymer seriously hindered the curing of silicone elastomer. The hindrance increased with increasing concentration of SWCNT and the quality of dispersion. The glass transition temperatures (T_g) of the nanocomposites were found to be independent of the SWCNT addition, although, the steps in the heat capacity (Δc_p) of the glass transition were smaller with increasing SWCNTs concentration. The melt crystallization behavior was strongly dependent on the concentration and dispersion of SWCNT in the polymer. The cooling scan showed that the higher concentration and the better dispersion of SWCNTs in the silicone resulted in higher percentage of melt crystallization of this nanocomposite. The correlation of the change of thermal properties to the dispersion of CNT in polymer may be used to determine the quality of SWCNT dispersion in silicone polymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1845–1852, 2008     

Structure d'un nouvel heteroside d'isoflavone: le sarothamnoside

The structure of sarothamnoside (genistein 7,4′-di-O-[4-O-β-D-glucopyranosyl-β-D-apiofuranoside]), a new isoflavone glycoside from $\text{Sarothamnus scoparius}$ and $\text{S}$, patens, has been established by spectral analysis, mainly ₁₃C NMR.     

Synthese ambidoselective d'enamines et d'imines siliciees

Trimethylchlorosilane reacts with organotin imines or enamines leading mainly (or only) to the corresponding silicon enamine. In contrast, the silylation of lithium or magnesium iminates gives only the isomeric imine when the nitrogen is hindered by bulky groups (i-Pr, t-Bu).The study of the NSi ? CSi equilibration shows clearly that in both cases the isomer obtained is the kinetic product of each reaction.These results show that a proper choice of both the metal associated with the iminate and of the iminate itself allows the formation of each isomer in a pure state.     

Couplage selectif d'azaallyllithium et d'arylallenes : synthese generale d'arylmethylenepyrrolidines

1–3 Cycloaddition of 1,3-diphenyl-2-azallyllithium with arylallenes affords a general synthetic method for arylmethylenepyrrolidines, a new class of five-membered-heterocycles.     

Determination de la constante d'acidite intrinseque d'un echangeur d'ions carboxylique

To obtain the intrinsic acidity constant of a carboxylic ion-exchanger, we propose a method of graphical double extrapolation. The results for an ion-exchanger made of polyvinyl alcohol grafted with acrylic acid are close to those published for the corresponding linear polyacid.     

Thermal stability and flammability of silicone polymer composites

Silicone polymer composites filled with mica, glass frit, ferric oxide and/or a combination of these were developed as part of a ceramifiable polymer range for electrical power cables and other high temperature applications. This paper reports on the thermal stability of polymer composites as determined by thermogravimetric techniques, thermal conductivity and heat release rate as measured by cone calorimetry. The effects of fillers on thermal stability and flammability of silicone polymer are investigated. Of the fillers studied, mica and ferric oxide were found to have a stabilising effect on the thermal stability of silicone polymer. Additionally, mica and ferric oxide were found to lower heat release rates during combustion, but only mica was found to increase time to ignition.     

Une synthese originale et inattendue d'isocoumarines fonctionnelles

Reaction of Ph₃P=CH-COOEt with ortho benzoyl benzoic acid derivatives offers an easy and surprising entry to functional isocoumarins via the thermal decomposition of the keto-ylide intermediates or by subsequent oxidization of the expected indenones.     

Coupures alcalines d'ethers bi-tertiaires et d'alcools

Heating αα′-tetrasubstituted ethers with sodium amide at 225–300° leads to smooth cleavage of one of the α-substituents, which is reduced in the process; the Intermediacy of an alkoxide ion is postulated, and a high yield cleavage of a tertiary alkoxide is indeed observed.     

Preparation d'acides aminoalkyl phosphoniques a l'aide d'ω-halogenoalkyl amines phosphorylees

Aminoalkylphosphonic acids are prepared via amino group protection by nitrogen-phosphorus (P-N) bond formation. Phosphorylation of β or γ-bromoalkylamines with chlorophosphates followed by reaction of the resulting haloalkylphosphoramidates with triethylphosphite (Arbuzov reaction) to give a phosphoramidate-phos-phonate intermediate which can be alkylated with various reagents. Removal of the phosphoryl residue may be brought about by treatment with aqueous hydrogen chloride. Improvements in the isolation of the amino-phosphonic acids are described.     

Composes d'addition entre les pentafluorures d'uranium et d'antimoine,preparation des composes UF5. n SbF5 (n = 1 ou2)

The adduct UF₅.2SbF₅ has been obtained from the reaction of UF₅ with SbF₅ and the reaction of UF₆ with SbF₅ in the presence of freon 114. From this preparation and also from studies on UF₆, SbF₅ solutions, the fluorinating properties of UF₆ were found to be enhanced by the presence of SBF₅. An x-ray diffraction study has shown that crystals of UF₅.2SbF₅ are monoclinic, space group P2₁/c, with unit cell dimensions a = 8.036(3) Å ; b = 14.112(13) Å ; c = 10.028(17) Å ; β = 96.91(7)°.The adduct UF₅.SbF₅ is obtained by thermal decomposition of UF₅.2SbF₅.