Si-C Bond Cleavage in Silyl Alkynes Under Phase-Transfer Catalysis. Applications to the Synthesis of Epoxyhexenynes

The alkaline cleavage of trimethylsilyl alkynes under PTC conditions is a mild and straightforward alternative to other methods. Applications of the new deprotection technique include the one-pot Darzensdesilylation reaction of trimethylsilyl alkynals without affecting the oxirane ring in the final products.     

Silica-immobilized N,O-prolinate ruthenium benzylidene complexes for catalytic applications

The immobilization of N,O-prolinate ruthenium benzylidene complexes as hybrid silicas is reported according to three routes: (i) co-condensation of a silylated precursor, 10, with TEOS via the sol–gel process (material M1); (ii) grafting of the same precursor on a preformed mesoporous silica M2 (material M3); entrapment of a parent non-silylated compound, 8, in the preformed mesoporous silica M2 (material M4). They have been characterized by several techniques. Solid state ²⁹Si NMR measurements ensure the anchorage of the Ru-complexed prolinate fragment in the silica matrix of M1 and M3 by the presence of T and Q sites, while only Q sites are observed as expected for M4. Elemental analyses provide the N/Si ratios and TGA experiments give the weight loss of the organics during decomposition and hence indicating the amount of organics inserted in the materials. Adsorption–desorption analyses show that these solids had surface areas ranging from 310 to 620 m²g^?1.These materials were tested as solid catalysts for two different reactions: ring-closing olefin metathesis and hydrosilylation of phenylacetylene with HSiEt₃. Their recyclability has also been investigated. While M1 is the less active for the first reaction giving low conversions and selectivity compared to M3 and M4, it is by far the most efficient catalyst for the second reaction.     

Segmental dynamics in poly(ε‐caprolactone)/poly(L‐lactide) copolymer networks

Poly(ε‐caprolactone) (PCL) and poly(lactic acid) (PLA) networks were prepared from macromonomer diols functionalized with methacrylic anhydride, which allows one to get self‐crosslinkable polymers. Besides, both macromonomers were copolymerized to get copolymer networks with different compositions (namely, PCL/PLA: 0/100, 70/30, 50/50, 30/70, 100/0). Dielectric and calorimetric experiments allow one to conclude the microphase separation of the system: one phase made of pure PCL domains while the second one consists of caprolactone units, which somehow plasticize PLA and moves its main relaxation (glass transition) to lower temperatures. The effect of crosslinking PLA on the dynamics of the system was further investigated by comparing with the dynamics for linear PLA. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 183–193, 2009     

Flux line lattice symmetries in the borocarbide superconductor LuNi2B2C

We compare the results of small angle neutron scattering on the flux line lattice (FLL) obtained in the borocarbide superconductor LuNi₂B₂C with the applied field along the c- and a-axes. For H‖c the temperature dependence of the FLL structural phase transition from square to hexagonal symmetry was investigated. Above 10 K the transition onset field. H ₂(T), rises sharply, bending away from H _c2(T) in contradiction to theoretical predictions of the two merging. For H‖a a first order FLL reorientation transition is observed at H _tr=3–3.5 kOe. Below H _tr the FLL nearest neighbor direction is parallel to the b-axis, and above H _tr to the c-axis. This transition cannot be explained using nonlocal corrections to the London model.     

Crosslinking study of mixtures of DGEBA and 1,3‐dioxan‐2‐one catalyzed by lanthanide triflates

Ytterbium and lanthanum triflates were used as catalysts to cure diglycidylether of bisphenol A with different proportions of 1,3‐dioxan‐2‐one. The curing was studied by differential scanning calorimetry (DSC) and Fourier transform infrared in the attenuated‐total‐reflection mode (FTIR/ATR). FTIR/ATR was used to monitor the competitive reactive processes and to quantify the evolution of the groups involved in the curing process. We observed the formation of a five‐membered cyclic carbonate that remains unreacted at the chain ends, because of an equilibrium process between the spiroorthocarbonates that had formed as intermediate species. The kinetics were studied by DSC experiments and analyzed with isoconversional procedures. The system catalyzed by ytterbium triflate had a higher curing rate. Thermogravimetric analysis and dynamic mechanical thermal analysis experiments were used to evaluate the properties of the materials obtained. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5799–5813, 2005     

Macroscopic, mesostructured cationic surfactant/neutral polymer films: structure and cross-linking

Mesostructured films of alkyltrimethylammonium bromides or cetylpyridinium bromide and polyethylenimines that spontaneously self-assemble at the air/water interface have been examined using a range of surface sensitive techniques. These films are unusual in that they can be micrometers thick and are relatively robust. Here we show that the films can be cross-linked and thus removed from the liquid surface where they form, as solid, mesostructured polymer-surfactant membranes. Cross-linking causes little change in the structure of the films but freezes in the metastable mesostructures, enhancing the potential of these films for future applications. Cross-linked films, dried after removal from the solution surface, retain the ordered nanoscale structure within the film. We also report grazing incidence X-ray diffraction (GID), which shows that most films display scattering consistent with 2D-hexagonal phase crystallites of rodlike surfactant micelles encased in polymer. Polymer branching makes little difference to the film structures; however, polymer molecular weight has a significant effect. Films with lower polymer MW are generally thinner and more ordered, while higher polymer MW films were thicker and less ordered. Increased pH causes formation of thicker films and improves the ordering in low MW films, while high MW films lose order. To rationalize these results, we propose a model for the film formation process that relates the kinetic and thermodynamic limits of phase separation and mesophase ordering to the structures observed.     

Non-Catalyzed C-Alkylation of Phenols With Cyclic Secondary Alkyl Bromides

C-Alkylations of phenol with 1-chloro and 1-bromoadamantane, 2-bromoadamantane, cyclohexyl bromide and exo-2-bromonorbornane, and C-alkylations of para-substituted phenol derivatives with 2-bromoadamantane are described.     

Inclusive π4He scattering and the πN interaction in the nuclear medium

Double differential cross sections for the inclusive reaction ⁴He(π, π′)X have been measured for six pion energies between 90 and 320 MeV and an angular range from 30° to 135°. The data are interpreted in terms of the Δ-hole formalism. Medium corrections to the free π-nucleon scattering operator are important for a quantitative understanding of our results. Total inelastic cross sections are obtained and estimates for the absorption cross section are given.