Aqueous room temperature metal-catalyzed living radical polymerization of vinyl chloride

This paper describes the room-temperature living radical polymerization (LRP) of vinyl chloride in H2O/THF in the presence of Cu0 or CuI salts as catalysts, tren or PEI as ligands, and iodoform as initiator. The disproportionation reaction 2CuI + L --> Cu0 + CuII(L) is the crucial step, as it continuously provides the active species for both the initiation (Cu0) and the reversible termination step (CuII). Mn was found to increase linearly with conversion and is in good agreement with Mth, with the Mw/Mn being approximately 1.5.     

Heat-shrinking spherical and columnar supramolecular dendrimers: their interconversion and dependence of their shape on molecular taper angle

Synthesis and modes of self-assembly are described for the tapered monodendritic molecules 3,4,5-nGi-X of generation i = 1, 2, 3 (see structures below) that contain multiple (CH2)nH alkyl chains on their periphery (n = 12, 14, 16) and a polar group X at the apex (X = COOH, COONa, COOCs, CO(OCH2CH2)3OH). These monodendrons self-assemble into supramolecular cylindrical or spherical dendrimers, which in turn self-organise into p6mm columnar or Pm3n cubic thermotropic liquid crystals, respectively. The two principal ways of affecting the self-assembly of these compounds by means of their molecular architecture are: a) by changing the width of the wide (aliphatic) end, and b) by changing the volume at the apex. In the present work a) is controlled through temperature (conformational disorder) and b) is controlled by chaging the generation number i or the size of X, for example, through the choice of metal cation. The single most important geometric parameter of these dendritic building blocks is the molecular solid angle (taper angle) alpha; a high alpha leads to spherical and a low alpha to cylindrical supramolecular dendrimers. Furthermore, alpha also determines the equilibrium size of the supramolecular objects; a larger alpha results in a smaller diameter. The unusually strong negative thermal expansion coefficient of the cubic and columnar lattice is attributed to the excess of the increasingly highly tapered molecules being rejected from their parent aggregates and reassembling as new ones. Increasing alpha is also considered to be responsible for the observed thermotropic columnar-cubic transition.     

Die Polymerisation von Acetylen-Derivaten. 25. Mitt. Synthese und Eigenschaften von isomeren Poly(β-äthynylnaphthalinen)

Ohne Zusammenfassung     

New carbazole-containing monomers and polymers

Five novel vinyl monomers, all of which contain 3-substituted carbazolyl groups [i.e., N-(9-ethyl-3-carbazolyl)-maleimide, 9-ethyl-3-carbazolyl acrylamide, 9-ethyl-3-carbazolyl methacrylamide, 9-ethyl-3-hydroxymethylcarbazolyl acrylate, and 9-ethyl-3-hydroxymethylcarbazolyl methacrylate], and their corresponding polymers were synthesized. Two methods were used for the synthesis of the last two monomers.     

Small angle x-ray analysis of the effect of temperature on the self-assembling columnar structures formed by a polymethacrylate with highly tapered side groups and by one of its low molar mass precursors

Small angle X-ray methods have been used to investigate the self-assembling columnar structures formed by a polymethacrylate with large highly tapered side groups, and by one of its low molar mass precursors. The polymer is poly{2-{2-[2-(2-methacryloyloxyethoxy)ethoxy] ethoxy}ethyl-3, 4, 5-tris(p-dodecyloxybenzyloxy)-benzoate} (H12-ABG-4EO-PMA); the precursor is 2-{2-[2-(2-hydroxyethoxy)-ethoxy]ethoxy}-ethyl-3, 4, 5-tris(p-dodecyl-oxybenzyloxy)benzoate (H12-ABG-4EO-OH). Both the polymer and the precursor form three dimensionally ordered structures at room temperature, consisting of hexagonally packed cylinders with diameters in the region of 60 and 53Å, respectively, in which the interiors of the columns probably have helical arrays of the stacked tapered groups. At higher temperatures these are converted to columnar hexagonal (ϕ_h) liquid crystalline phases. At temperatures close to this transition for the precursor we detect two coexisting columnar structures, with the ϕ_h structure having a diameter approximately 1Å higher than that in the solid state. For the polymer, the data are not so well resolved, and coexisting phases cannot be resolved. However, the changes in column dimensions are larger than for the precursor. Conversion of the room temperature phase to the ϕ_h phase at 40°C results in an increase of 3Å in the diameter, which then declines by approximately the same amount as the temperature rises to 90°C, close to the isotropization point. Cooling to room temperature does not immediately restore the room temperature structure. Rather, we obtain a quenched ϕ_h structure, with a column diameter almost 10% higher. These dimensional changes correlate well with the changes in diameter with temperature seen for the bulk fiber, and suggest a continuous rearrangement of the interiors of the columns in the ϕ_h phase, such as a partial unwinding of a disordered helical structure.     

Total Syntheses of Cyanthiwigins B,F, and G

A concise and versatile approach toward the preparation of the cyanthiwigin family of cyathane natural products is described. By leveraging a unique double asymmetric catalytic alkylation procedure it is possible to quickly establish two of the most critical stereocenters of the cyanthiwigin framework with high levels of selectivity and expediency. The synthetic route additionally employs both a tandem ring‐closing cross‐metathesis reaction, and an aldehyde‐olefin radical cyclization process, in order to rapidly arrive at the tricyclic cyathane core of the cyanthiwigin molecules. From this unifying intermediate, the preparations of cyanthiwigins B, F, and G are attained swiftly and without the need for protecting groups.     

Phase formation, crystal chemistry, and properties in the system Bi2O3-Fe2O3-Nb2O5

Subsolidus phase relations have been determined for the Bi₂O₃-Fe₂O₃-Nb₂O₅ system in air (900-1075 °C). Three new ternary phases were observed—Bi₃Fe_0.5Nb_1.5O₉ with an Aurivillius-type structure, and two phases with approximate stoichiometries Bi₁₇Fe₂Nb₃₁O₁₀₆ and Bi₁₇Fe₃Nb₃₀O₁₀₅ that appear to be structurally related to Bi₈Nb₁₈O₅₇. The fourth ternary phase found in this system is pyrochlore (A₂B₂O₆O′), which forms an extensive solid solution region at Bi-deficient stoichiometries (relative to Bi₂FeNbO₇) suggesting that ≈4-15% of the A-sites are occupied by Fe³⁺. X-ray powder diffraction data confirmed that all Bi-Fe-Nb-O pyrochlores form with positional displacements, as found for analogous pyrochlores with Zn, Mn, or Co instead of Fe. A structural refinement of the pyrochlore 0.4400:0.2700:0.2900 Bi₂O₃:Fe₂O₃:Nb₂O₅ using neutron powder diffraction data is reported with the A cations displaced (0.43 Å) to 96g sites and O′ displaced (0.29 Å) to 32e sites (Bi_1.721Fe_0.190(Fe_0.866Nb_1.134)O₇, Fd3¯m (#227), ). This displacive model is somewhat different from that reported for Bi_1.5Zn_0.92Nb_1.5O_6.92, which exhibits twice the concentration of small B-type cations on the A-sites as the Fe system. Bi-Fe-Nb-O pyrochlores exhibited overall paramagnetic behavior with large negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. The single-phase pyrochlore with composition Bi_1.657Fe_1.092Nb_1.150O₇ exhibited low-temperature dielectric relaxation similar to that observed for Bi_1.5Zn_0.92Nb_1.5O_6.92; at 1 MHz and 200 K the relative permittivity was 125, and above 350 K conductive effects were observed.     

Thermal stability of gamma-irradiated polyurethane/POSS hybrid materials

Through temperature-programmed pyrolysis, the physicochemical properties of Pteria martensii (PM) before and after calcination are investigated. Our results show that the mass loss is 11.02% from room temperature to 600 °C with an average mass loss rate of 0.19% per min. The decomposition of organics coupling with the phase transition of calcium carbonate from aragonite to calcite occurs in the range of 367.4–423.0 °C, as confirmed by X-ray diffraction and Fourier transform infrared spectroscopy analyses. The decomposition pores and channels are changed forming complex porous structures. The surface of sample shows a much rougher fracture, with higher C, O and N element concentrations. At the stage of decomposition and phase transition of organics, the average activation energy value is 118.78 kJ mol^?1. This study provides valuable information on the calcination process and calcined PM for use in medicines.