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71.
72.
Rb3ReH10, a New Rhenium(VII) Hydride – High Pressure Synthesis and Crystal Structure The ternary hydride Rb3ReH10 can be synthesised by reacting rubidium hydride with rhenium in a hydrogen atmosphere under a pressure of above 4000 bar in a temperature range between 700 and 870 K. X-ray investigations on powder samples and elastic neutron diffraction experiments on the deuterated compound led to the crystal structure. According to the formula [ReD9]DRb3 the atomic arrangement of the room temperature modification corresponds to that of the perowskite structure type. The coordination polyhedron of the hydrogen atoms that surround each rhenium atom can be described crystallographically as a statistical occupation of two 24-fold positions with hydrogen. In the orthorhombic low-temperature modification the deuterium ligands are arranged in ordered positions. They form monocapped square antiprisms. Magnetic susceptibility measurements revealed Rb3ReD10 to be diamagnetic. 相似文献
73.
Uwe Engelmann Gudrun Schmidt-Naake Jens Maier Peter Seifert 《Macromolecular theory and simulations》1994,3(5):855-883
With the help of a simple reaction-diffusion model with constant striation thickness the influence of micromixing on free-radical polymerization was investigated for several test reactions with discontinuous prepolymerization and jerky addition of selected reactants. Monomer conversion or mean values of molar mass and chemical composition cannot be expected to be very sensitive to micromixing effects. If molar mass distributions are to be used, problems will arise from the fact that the distribution of the polymer accumulated during prepolymerization covers mixing influences occurring after reactant feed. The instantaneous molar mass distribution would be more suitable. Time-integral distributions of chemical composition or sequence length in combination with appropriate test reactions proved to be feasible indicators for the effects of micromixing as it becomes possible to separate the distribution of the prepolymer from that of the polymer which is formed after addition when micromixing is to be investigated. 相似文献
74.
The orientation of macromolecular chains in two melt-spun polymer fibers (segmented polyurethane elastomer and melt-modified polyolefine fibers) was studied by photoacoustic spectroscopy (PAS) with polarized light in the mid-infrared range. The PAS orientation functions calculated from the photoacoustic signal intensities of orientation sensitive bands describe the orientation of the different chain segments with respect to the fiber axis. Thus, the orientation of hard and soft segments in the unstressed polyurethane fiber is different and both are similiar to that of the corresponding injection molded bars. With increased spinning velocity an improved orientation of the polyolefine chains along the fiber axis, but only in the amorphous regions of the polymer, were detected. Only a slight reduction of orientation was measured as a result of the subsequent chemical crosslinking in the polyolefines. 相似文献
75.
76.
G. Auffermann G. Auffermann A. Simon Th. Gulden G. J. Kearley G. J. Kearley A. Ivanov 《无机化学与普通化学杂志》2001,627(3):307-311
We report on the incorporation of hydrogen into La2C3 and on the characterisation of its position. Temperature‐dependent X‐ray investigations show that the hydrogenation process is reversible and the product La2C3H1.5 is amorphous. In principle, IR and Raman spectroscopies can provide some structural information, but in the present study, they are of only limited value. Inelastic neutron scattering (INS) has advantages for measuring the H‐vibrations in La2C3H1.5 and these are compared with the results of molecular dynamics simulations. A structural model based on published pair‐potentials predicts that hydrogen (or deuterium) occupies the “tetrahedral” holes in the lanthanum sublattice. This model also accounts for the observed vibrational spectra. 相似文献
77.
Ulrich Wendler Jrg Bohrisch Werner Jaeger Gudrun Rother Herbert Dautzenberg 《Macromolecular rapid communications》1998,19(4):185-190
N-oxyl terminated vinylbenzyl chloride macromonomers, available via controlled free radical polymerization, were used to synthesize AB-block copolymers of vinylbenzyl chloride and styrene with low polydispersity and different block lengths and block length ratios. The vinylbenzyl chloride blocks were quantitatively converted into cationic polyelectrolytes by reactions with tertiary amines. The micellization of the synthesized amphiphilic cationic block copolymers was investigated using different techniques such as static light scattering, ultracentrifugation and size exclusion chromatography. 相似文献
78.
Stefan Wuttke Dipl.‐Chem. Simona M. Coman Prof. Dr. Gudrun Scholz Priv.‐Doz. Dr. Holm Kirmse Dr. Alexandré Vimont Dr. Maro Daturi Prof. Dr. Sven L. M. Schroeder Dr. Erhard Kemnitz Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(36):11488-11499
Novel magnesium fluorides have been prepared by a new fluorolytic sol–gel synthesis for fluoride materials based on aqueous HF. By changing the amount of water at constant stoichiometric amount of HF, it is possible to tune the surface acidity of the resulting partly hydroxylated magnesium fluorides. These materials possess medium‐strength Lewis acid sites and, by increasing the amount of water, Brønsted acid sites as well. Magnesium hydroxyl groups normally have a basic nature and only with this new synthetic route is it possible to create Brønsted acidic magnesium hydroxyl groups. XRD, MAS NMR, TEM, thermal analysis, and elemental analysis have been applied to study the structure, composition, and thermal behaviour of the bulk materials. XPS measurements, FTIR with probe molecules, and the determination of N2/Ar adsorption–desorption isotherms have been carried out to investigate the surface properties. Furthermore, activity data have indicated that the tuning of the acidic properties makes these materials versatile catalysts for different classes of reactions, such as the synthesis of (all‐rac)‐[α]‐tocopherol through the condensation of 2,3,6‐trimethylhydroquinone (TMHQ) with isophytol (IP). 相似文献
79.
80.