Nachweis, Bestimmung und Trennung des Zirkoniums von anderen Elementen

Ohne Zusammenfassung     

Two-dimensional analysis of the SAXS of partially oriented polymers*)

The Small-angle X-ray scattering (SAXS) patterns of oriented LDPE (λ=1...5.7) were fitted by calculating the small-angle intensity for a structure consisting of a linear paracrystalline lattice built up by finite lamellar or cylindrical crystallites. The resulting data of the superstructure were compared with corresponding values from wideangle X-ray scattering. It is shown that it is impossible to get quantitative information about the superstructure of oriented polymers by using SAXS alone. Nevertheless, the qualitative transition of the crystals during orientation can be explained very well.     

Halogenzahlen der Fette

Ohne Zusammenfassung     

Four novel spirooxazacamphorsultam derivatives

The chiral compounds (6aS,9S,10aR)‐11,11‐dimethyl‐5,5‐dioxo‐2,3,8,9‐tetrahydro‐6H‐6a,9‐methanooxazaolo[2,3‐i][2,1]benzisothiazol‐10(7H)‐one, C₁₂H₁₇NO₄S, (1), (7aS,10S,11aR)‐12,12‐dimethyl‐6,6‐dioxo‐3,4,9,10‐tetrahydro‐7H‐7a,10‐methano‐2H‐1,3‐oxazino[2,3‐i][2,1]benzisothiazol‐11(8H)‐one, C₁₃H₁₉NO₄S, (2), (6aS,9S,10R,10aR)‐11,11‐dimethyl‐5,5‐dioxo‐2,3,7,8,9,10‐hexahydro‐6H‐6a,9‐methanooxazolo[2,3‐i][2,1]benzisothiazol‐10‐ol, C₁₂H₁₉NO₄S, (3), and (7aS,10S,11R,11aR)‐12,12‐dimethyl‐6,6‐dioxo‐3,4,8,9,10,11‐hexahydro‐7H‐7a‐methano‐2H‐[1,3]oxazino[2,3‐i][2,1]benzisothiazol‐11‐ol, C₁₃H₂₁NO₄S, (4), consist of a camphor core with a five‐membered spirosultaoxazolidine or six‐membered spirosultaoxazine, as both their keto and hydroxy derivatives. In each structure, the molecules are linked via hydrogen bonding to the sulfonyl O atoms, forming chains in the unit‐cell b‐axis direction. The chains interconnect via weak C—H...O interactions. The keto compounds have very similar packing but represent the highest melting [507–508 K for (1)] and lowest melting [457–458 K for (2)] solids.     

Conformational distinguishability of medium cycloalkanes in crystals via inelastic neutron scattering

This paper begins an exploration of the use of the combination of DFT computations with experimental inelastic neutron scattering (INS) spectra as a method for establishing what conformation is present in a molecular crystal at low temperature. Presented here are INS spectra of a series of medium-sized cycloalkanes: C6H12, C7H14, C8H16, C10H20, C12H24, and C14H28. Optimized geometries and normal mode calculations were performed at B3LYP/6-311G(d,p) on the lowest energy conformations (i.e., those thermally accessible at the experimental temperature of 30 K). The calculated and observed spectra were analyzed for the best fit from each set of conformers, allowing a prediction of the dominant conformation in a conformationally rich system. For each cycloalkane, the calculated spectrum for the lowest energy conformer shows good agreement with experiment while the higher energy conformations have a much poorer fit. With little ambiguity, the lowest energy conformer is therefore predicted to be the dominant conformation, consistent with the diffraction data available for C6H12, C10H20, C12H24, and C14H28. These results indicate that INS spectroscopy may be a useful tool in determining the dominant conformation in a crystal lattice in cases such as this in which the intermolecular interactions are weak and the different conformers are calculated to have distinguishable spectra. Such an analysis is applied to the cases of C7H14 and C8H16 for which no low-temperature X-ray analysis is available. Clear structure predictions result, and the conformer observed is that computed to be of lowest energy for the molecule in isolation.     

Wide-and small-angle x-ray scattering studies on the real structure of fractions of (ethylene-α-olefine)-copolymers

Fractions according to the degree of branching of (Ethylene/1-Buten)-Copolymer (LLDPE) were investigated by wide-and small-angle scattering. The thickness of the crystallites is nearly independent of the degree of branching and their volumes reach a limit according to the smallest stable crystal. The mean lattice disfortions also do not change remarkably with the degree of branching but the components of theg _ik tensors do so. The possibility of partial incorporation of side groups into the crystal lattice is discussed. Comparison of wide-and small-angle scattering shows that only the part of the crystallites with smaller thickness builds lamellar clusters while thicker ones are individual crystals.Dedicated to Prof. Dr. W.Pechhold on the occasion of his 60th birthday     

The “Nickel Effect”

Whereas the reaction of ethylene and triethylaluminum under pressure at 100°C yields trialkylaluminum compounds having long alkyl chains, the presence of small amounts of nickel salts induces the formation of butene. The discovery of this “nickel effect” represents the starting point for the development of the Ziegler catalysts. Comparatively little was formerly known about the nature and the mode of action of the catalytically active nickel species. A basis for the elucidation of the effect was provided by studies on the reduction of nickel compounds by organoaluminum compounds, on the occurrence and existence of nickel hydrides, and on interactions between nickel(0) and Lewis acids as well as organic compounds of main group metals. The most significant result of these studies is the recognition that multicenter bonding systems involving trialkylaluminum compounds and nickel atoms are involved. These react further with complex bonded ethylene in what is probably a concerted manner.     

Determination of crystallite particle size distribution of polymers from WAXS

A method for the calculation of crystallite size distributions from the profile of wide-angle x-ray reflections is developed. The influence of lattice distortions on the profile is taken into account. The information about the lattice distortions is obtained from the measurement of the integral widths of a number of reflections. The method is applied to samples of (ethylen-1 hexen) copolymers. The change of crystallite size distributions in lateral directions with increasing temperature (20–121°C) is measured. Recrystallization processes at temperatures near the melting point are observed. © 1996 John Wiley & Sons, Inc.