Oligomérisation anionique de l'ethylène. II. Etude des paramètres thermodynamiques

A kinetic study, as a function of temperature, of ethylene oligomerization by the n-BuLi–TMEDA complex allowed us to evaluate the thermodynamic parameters (ΔS^? < ?23.7 u.e.) and thus to support a transition state where the ethylene is coordinated to the lithium atom.     

Alumina interaction with AMPS-MPEG random copolymers I. Adsorption and electrokinetic behavior

Adsorption of brush copolymers, bearing sulfonate groups and polyethylene glycol segments, on to alumina particles in suspension in water has been investigated. Study of the adsorption isotherms revealed that the copolymers displayed a strong affinity for the surface of the alumina regardless of the fraction of ionic groups on the polymer. For poly(ethylene glycol) content greater than 50%, the adsorption isotherms revealed an initial adsorption plateau followed by a second one. The shape of the adsorption isotherms was interpreted in terms of the polymer configuration at the solid-to-liquid interface. The effects of the pH and the ionic force on adsorption were studied and connected to the effects of interaction between chain segments at the surface of the alumina particles. Changes in the electrokinetic properties of the alumina particles after addition of the copolymers were investigated by following the zeta potential of particles as a function of pH. In the presence of the copolymer continuous shift of the isoelectric point IEP to a more acidic values was observed. Beyond a certain concentration the zeta potential remained negative regardless of the pH.     

Highly diastereoselective Diels-Alder reactions of Baylis-Hillman adducts

[reaction: see text] Baylis-Hillman adducts were found to be excellent dienophiles in Diels-Alder reactions, providing essentially complete diastereocontrol (although mixtures of endo/exo isomers) with all dienes.     

Energy transfer in poly(3‐hexylthiophene)‐g‐Polyfluorene graft copolymers

Conjugated graft copolymers consisting of a poly(3‐hexylthiophene) (P3HT) backbone and poly(9,9'‐dioctylfluorene) side chains (PF) with different grafting degrees were synthesized by the CuAAC reaction. The properties of these materials were studied by UV‐Vis and fluorescence spectroscopy. The former technique provides insight in their self‐assembly, while the latter is used to study the energy funneling from the PF side chains to the P3HT backbone. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1252–1258     

On the classification of partition quantum groups

This is a survey on some results obtained recently in the classification of compact quantum groups associated to partitions, with a focus on the non-crossing case. We take a global look at the main results in the subject and highlight some key features of the methods used. We conclude by several suggestions for pushing further the classification.     

Alumina interaction with AMPS-MPEG random copolymers III. Effect of PEG segment length on adsorption, electrokinetic and rheological behavior

The effect of different 2-acrylamido-2-methylpropanesulfonic acid sodium salt (AMPS)-methoxypolyethyleneglycol methacrylate (MPEG) comb-like copolymers on the adsorption behavior, electrokinetic and rheological properties of alumina suspensions has been investigated. The change in adsorption isotherms with the content of the two monomers, the medium pH and the ionic strength indicated that the interaction of these copolymers was found to be controlled by both the fraction of ionic groups on the polymer and by the length of the polyethyleneglycol (PEG) segments. Adsorption of the copolymers on alumina particles is accompanied by a shift in the IEP toward acid pH values and may lead to a charge reversal above a certain level. The presence of the PEG segment equally affects the magnitude of the zeta potential by moving the shear plane forward. Addition of the copolymers greatly affects the rheological behavior of the suspension; the viscosity at a defined shear rate decreases and reaches an optimum, which is all the lower as the fraction of the ionic groups is higher. The dispersing effect of the copolymer was controlled by both the ionization level of the copolymer and by the length of the PEG segments.     

Selective ortho-Functionalization of Adamantylarenes Enabled by Dispersion and an Air-Stable Palladium(I) Dimer

Contrary to the general belief that Pd-catalyzed cross-coupling at sites of severe steric hindrance are disfavored, we herein show that the oxidative addition to C−Br ortho to an adamantyl group is as favored as the corresponding adamantyl-free system due to attractive dispersion forces. This enabled the development of a fully selective arylation and alkylation of C−Br ortho to an adamantyl group, even if challenged with competing non-hindered C−OTf or C−Cl sites. The method makes use of an air-stable Pd^I dimer and enables straightforward access to diversely substituted therapeutically important adamantylarenes in 5–30 min.     

Géométrie toroïdale et géométrie analytique non archimédienne. Application au type d’homotopie de certains schémas formels

V.G. Berkovich’s non-Archimedean analytic geometry provides a natural framework to understand the combinatorial aspects in the theory of toric varieties and toroidal embeddings. This point of view leads to a conceptual and elementary proof of the following results: if X is an algebraic scheme over a perfect field and if D is the exceptional normal crossing divisor of a resolution of the singularities of X, the homotopy type of the incidence complex of D is an invariant of X. This is a generalization of a theorem due to D. Stepanov.     

Effects of surface properties on the impact process of a yield stress fluid drop

The impact of a yield stress fluid drop onto a solid surface with diversified interface properties has been experimentally investigated. Two smooth substrates with distinct surface energies and three similar substrates with different roughnesses have been used. The bulk shear rheological behaviour of Carbopol gels, concentrated suspensions of swollen micro-gels, has been measured. Wall friction has also been characterized on each substrate. Slip effects of gels proved to be greater on a more hydrophobic substrate. They decreased with an increase in roughness. The drop hydrodynamics during the impact was correlated with the wall friction of the gels on all substrates and with the ratio of surface roughness to size of the swollen micro-gels. At very low impact velocities, the gravitational subsidence amplitude depends greatly on surface properties. At higher impact velocities, no significant difference is observed during the spreading phase. The drop behaviour differs during the retraction depending on the substrate. Interface effects during the retraction stage proved to diminish when the yield stress value increases.