Comportement en photooxydation de quelques polymeres du chlorure de vinyle contenant des structures oxygenees

We have studied the photooxidation of PVC samples modified by introduction of oxygen, carbon monoxide or acetylenic diester (ADCE) in the polymerisation medium. The presence of O₂ and (or) CO results in photosensitization, principally due to the conjugated polyenes. These groups are formed in a zip elimination reaction initiated by thermolabile oxygenated groups such as α-chloro peroxide or β chloroketones. The fumarate structures, formed during the PVC-ADCE copolymerization, play a stabilizing role at a concentration near to 0.10%. The inhibition mechanism has not been elucidated.     

Optical Detection and Spectroscopy of Single Molecules

The optical study of single molecules opens new paths in molecular spectroscopy, solid state physics and quantum optics. And recent experiments at room temperature hold great promise for chemistry and biology as well     

Approaches toward the synthesis of 2,5-disubstituted-1,3-thiazolidines

Synthetic approaches for new 2,5-disubstituted-1,3-thiazolidines are described. Steric and electronic effects of the N-substituent of the thiazolidine ring represent the major parameter in the rearrangement process. The nmr studies demonstrate that N-unsubstituted 2,5-disubstituted-1,3-thiazolidines exist as epimeric mixture, while the corresponding N-acetylated analogues exist as a conformer mixture.     

Noncommutative homology of some three-dimensional quantum spaces

We compute the Hochschild and cyclic homology of certain three-dimensional quantum spaces (type A algebras), introduced by Artin and Schelter. We show that the Hochschild homology is determined by the quasi-classical limit.     

Diffusion Crosslinking Kinetics of Thermoset Polymers

The problem of the delayed crosslinking arising due to the diffusion of a crosslinker molecule from a vector particle within a thermoset polymer matrix is discussed. The crosslinker molecules, initially embedded in the vector particles, diffuse from the particle to the polymer matrix and react with the functional groups grafted to polymer chains. The two‐step diffusion crosslink kinetics is studied theoretically on the example of polyethylene functionalized with anhydride groups reacting with 1,4‐butanediol as a crosslinker molecule. This provides the independent of time limiting distribution functions of the concentration of crosslinks, unreacted and intermediate functional groups, which are shown to be rather sensitive to system parameters as rates of chemical reactions, ratio of diffusion coefficients of matrix to vector particles, stoichiometric composition of the reactive groups, etc. The nonmonotonic distribution of the crosslink concentration around the vector particles at certain range of the parameters is revealed.

     

Maharam's problem

We solve Maharam's problem [D. Maharam, An algebraic characterization of measure algebras, Ann. Math. 48 (1947) 154–167. [3]], also known as the Control Measure Problem. We construct a non-zero exhaustive submeasure on the algebra of clopen sets of the Cantor set that is not absolutely continuous with respect to a measure. To cite this article: M. Talagrand, C. R. Acad. Sci. Paris, Ser. I 342 (2006).     

Photoinduced magnetism caused by charge-transfer excitations in tetracyanoethylene-based organic magnets

The photoinduced magnetism in Mn-tetracyanoethylene (TCNE) molecule-based magnets is ascribed to charge-transfer excitations from manganese to TCNE. Charge-transfer energies are calculated using density functional theory; photoinduced magnetization is described using a model Hamiltonian based on a double-exchange mechanism. Photoexciting electrons from the manganese core spins into the lowest unoccupied orbital of TCNE with photon energies around 3 eV increase the magnetization through a reduction of the canting angle of the manganese core spins for an average electron density on TCNE less than one. When photoexciting with a smaller energy, divalent TCNE molecules are formed. The delocalization of the excited electron causes a local spin flip of a manganese core spin.