The α transition in Fe1−xMxS materials (M = Mn,Cr): Physical and structural aspects

For Fe_1?xM_xS, the NiAs-type solid solution is limited to x < 0.12, and the materials exhibit a low-temperature FeS-type behavior with an α transition. Fe_1?xM_xS, the low-temperature solid solution is limited to x < 0.08, and for higher Cr concentration a high-temperature FeS-type behavior is observed. Resistivities and magnetic susceptibilities reveal the progressive weakening of the α transition for increasing Mn or Cr concentration.Crystal structure determination of Fe_0.96Mn_0.04S and Fe_0.955Cr_0.045S establish that the superstructure (a√3, 2c) weakening is due to the formation of disordered domains induced by the M substitutions.Physical and structural results are discussed together and lead to an interpretation of the α transition, whether induced by temperature or impurities, as a transition between a nondegenerated polaron gas, at low temperature or for x_Cr < 0.08, and a degenerated polaron gas for T > T_α or for x_Cr > 0.08. The validity of this polaron model is discussed in the case of Fe_1?xM_xS.     

Efficient photochemical synthesis of tricyclic keto‐indoles

Tricyclic keto‐indoles were synthesized by photocyclization of easily obtained enaminones in an electro‐cyclic photochemical reaction. The three methods reported were chosen according to the enaminone structure. The most general procedure using one‐step synthesis was carried out in a benzene‐methanol solution in the presence of sodium methylate. In the case of base sensitive substrates, the best method was photocyclization followed by oxidation. Besides, N‐unsubstituted indoles with a five‐membered ring were prepared by a photolysis reaction. All three methods are efficient and easy to perform.     

Degradation of epoxy resins under high energy electron beam irradiation: Radio-oxidation

The degradation of two epoxy systems exposed to electron beam irradiation in oxygen atmosphere has been studied and compared to our previous results obtained under helium atmosphere. A multi-scale approach to the degradation has been carried out using a variety of analytical methods including solid state NMR spectroscopy, 2D-WISE experiments, SEC measurements and infrared spectroscopy associated with chemical derivatisation treatments. It is shown that the degradation of both polymers is governed by radiolytic processes which involve chain scissions. The formation of oxidation products, mainly carboxylic acid chain ends, was shown at the surface of the irradiated film. Oxidative degradation is limited to the first 20 μm of the film due to the low oxygen diffusion coefficient in epoxy polymers combined with the high dose rates of irradiation.     

Photooxidation of polypropylene/layered double hydroxide nanocomposites: Influence of intralamellar cations

The influence of layered double hydroxides (LDHs) on the photooxidation of polypropylene (PP)/LDH nanocomposites was studied under irradiation at long wavelengths (λ > 300 nm, 60 °C and in the presence of oxygen). The influence of hybrid LDHs containing different divalent cations (Mg, Zn or both Mg and Zn) on the photooxidation mechanism of PP and on the rates of oxidation of the matrix was characterised based on infrared analysis. The presence of LDHs modifies the photoproducts accumulating in the PP and the rates of oxidation of PP were changed depending on the divalent cations in the LDH layers. Whereas natural clays, such as montmorillonite (MMt), can lead to a faster degradation of the materials, LDHs (Zn₂-Al-DS, for example) appear to have no inductive effect on polymer oxidation.     

Photoageing behaviour of epoxy nanocomposites: Comparison between spherical and lamellar nanofillers

The photochemical behaviour of a nanofilled epoxy resin has been studied. It has been shown that the filler content increases at the surface with irradiation time. Qualitative stiffness and adhesion measurements compare the surface properties of the filled and unfilled samples upon ageing. Depth profiling has been achieved by AFM nanoindentation and micro-FTIR. These two techniques allowed comparing stiffness and photooxidation of the aged samples. Both techniques showed an influence of nanofillers on thickness profiles. The relationship between the oxidation process and its consequences on the physical properties is explained taking into account oxygen permeability and light diffusion. Additionally, it has been shown that, whatever the content (5-10 wt%), the nature (silica or different organo-modified montmorillonites) or the shape of the filler (spherical or lamellar), the photoproducts were formed in comparable proportions and at similar rates as in the pristine matrix.     

General methodology for the synthesis of conjugated dienic insect sex pheromones

A general methodology for the synthesis of various types of dienic insect sex pheromones (Z-E, E-Z, Z-Z) is based on the carbocupration of acetylene by functionalised or non-functionalised lithium dialkyl cuprates, followed by the coupling of the resulting Z dialkenyl cuprates with functionalised or non-functionalised E or Z alkenyl iodides under Pd° catalysis. The following compounds were efficiently synthesized with a high degree of stereoisomeric purity: (E-Z)7, 9-dodecadien,-l-yl acetate 1 (Lobesia botrana), (E-Z)10, 12-hexadecadien,-l-ol 2 (Bombyx mori), (Z-E)9, 11-tetradecadien,-l-yl acetate 3Spodoptera littoralis), (Z-E)5, 7-dodecadien-l-ol 4 (Malascoma disstria), (Z-Z)11, 13-Hexadecadien-l-al 5 (Amyelois transitella), (Z)9,ll-dodecadien-l-yl acetate 6 (Diparopsis castanea) and (Z-Z)9,11-tridecadien-l-yl acetate 22 (a known “pseudo-pheromone”).     

Synthesis and Diels-Alder Reactions of a New Kind of Chiral Dienophiles: Cyclic Vinyl-p-tolylsulfilimines

A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group.     

Zeros of the Whittaker function associated to Coulomb waves

The zeros in the complex z plane of the Whittaker function W_c/z,µ(z),closely related to spherical waves in the quantum-mechanicalCoulomb problem, are investigated for varying real values ofthe parameters c and µ