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991.
The influence of catalysis on chemical modification of 1,2-polybutadienes (Mn < 10,000) by CX3Z reagents (X = halogen; Z = functional group or halogen), in order to obtain polymers soluble in common solvents, has been studied. The work has been carried out with carbon tetrachloride, trichloromethylphosphonyldichloride (CCl3POCl2) and ethyl trichloroacetate (CCl3CO2Et) in the presence of solvents such as C6H6, CH2Cl2. Among the compounds tested as catalysts for the addition of CX3Z to 1,2-polybutadiene (transition metal salts and complexes; radical initiators) only the systems formed with metal salts such as CuCl2, FeCl3, RuCl3 3H2O, Fe2(CO)9 and Cl2Ru(PPh3)3 were found to show high catalytic activity. The most active is Cl2Ru(PPh3)3: used without or with cocatalysts (Et3NHCl/benzôin, alcohols), it leads always, to the best yields whatever the nature of CX3Z. The activity of the other catalysts is generally dependent on CX3Z structure. Some secondary reactions (cross-linking, cyclization, transesterification) have been found.  相似文献   
992.
We report on the luminescence of doped and undoped PbMoO4 and PbWO4 single crystals; a red emission is found for the first time for PbMoO4. The degree of polarization of both the emissions of PbWO4 and of the shorter-wavelength emission of PbMoO4 is measured. The shorter-wavelength emissions are assigned to the 3T11A1 transition in the tetrahedral MoO42?(WO42?) group. It is assumed that the 3T1 level is split due to spin-orbit coupling. The longer-wavelength emissions are assigned to a transition in a molybdate (tungstate) group lacking an oxygen ion, i.e., a MoO3(WO3) group.  相似文献   
993.
Ohne Zusammenfassung Die Arbeit wurde aus Mitteln des Marshall-Planes (ERP-Mittel) und mit Spenden aus dem „Fonds Chemie“ ausgeführt. Wir sprechen den zust?ndigen Stellen für die Gew?hrung der Beihilfe unseren verbindlichsten Dank aus. Der Deutschen Forschungsgemeinschaft danken wir für die überlassung einer Ultrazentrifuge, den Behring-Werken für die uns zur Verfügung gestellten Serumalbumin- und -globulin-Pr?parate.  相似文献   
994.
It was derived theoretically that a sharp end-point of this spectrophotometrical titration is defined, in order of importance, by: 1. *KC ? *KI (numerically speaking, log*KC*KI should be at least 4); 2. *KI being large (numerically e.g. 104-105); this is already reached by choosing a high pH; 3. it being low; 4. mt being as high as possible.  相似文献   
995.
A study of the extraction of chromium(VI) from aqueous media by ketones was made. Extraction of chromium was found to be most efficient from aqueous hydrochloric acid solutions. A mechanism for the extraction of chromium(VI) from aqueous hydrochloric acid solutions by methyl isobutyl ketone is proposed involving the formation of a receptor in the organic phase, the exchange of the chloride ion of the receptor for the anionic chromium(VI) species of the aqueous phase, and the solvation of the extracted chromium species. The differences in the abilities of various ketones to extract chromium(VI) from aqueous hydrochloric acid solutions, and the differences in the extraction of chromium (VI) from various aqueous acids by methyl isobutyl ketone are attributed to the differences in the formation of receptors.  相似文献   
996.
Development of the techniques of ion kinetic energy spectrometry and mass-analyzed ion kinetic energy spectrometry is described. The extension of these concepts to the method of tandem mass spectrometry for direct mixture analysis is traced, and a rationale for the construction of hybrid mass spectrometers is presented. Collisions of polyatomic ions with surfaces are discussed as an outgrowth of gaseous collisions. An attempt is made to describe a philosophy of research that guided the construction of a dozen mass spectrometers and the exploration of organic ion chemistry in as many contexts.  相似文献   
997.
The microstructure of tetrahydrofuran (A)-3,3 dimethyloxetane (B) copolymers was studied by 13C-{1H}-NMR spectroscopy. Only the methyl carbons corresponding to the 3,3 dimethyloxetane unit appear as a singlet, whereas the other carbons present a more complicated spectral pattern than it would be expected if ? effects were negligible. The assignment of the resonance signals allowed the determination of the values of the probabilities of the different triads, which were in good agreement with those obtained from the reactivity ratios.  相似文献   
998.
The surface morphology of a number of films of AB block copolymers of polydimethylsiloxane and polystyrene was examined by ESCA and contact angle measurements. In all cases the immediate surface is shown to consist of an essentially pure polydimethylsiloxane component. By comparing the intensities of elastic peaks corresponding to photoionizations from core levels without energy loss for polydimethylsiloxane and polystyrene with those for the block copolymers and by consideration of shake-up phenomena specific to the polystyrene component, an estimate of the thickness of the polydimethylsiloxane outer layer of the latter may be obtained. This is shown to vary between ~13 and 40 Å, depending on the method of formation of copolymer film.  相似文献   
999.
Thermal analysis supported by kinetic calculations was applied exhaustively to these compounds. Under dynamic conditions, tetrafluorometallates(III), which as intermediates, could not be isolated, for the first three compounds. In each case, the final step was the pure metal(III) fluoride. Ammonium hexafluorochromate(III) decomposed directly to the pure chromium(III) fluoride. The decomposition rate of all compounds slowed down towards the end, probably for kinetic reasons. Polymorphic transitions of ammonium hexafluorotitanate(III) were observed at 35 and 100°C. Ammoniumhexafluoroscandate(III) underwent polymorphic transition at 47°C. The decomposition patterns for all these compounds were similar. Conditions for the preparation of pure ammonium tetrafluorometallates(III) of Sc, Ti and V are described.  相似文献   
1000.
We have accomplished the intramolecular oxymercuration of γ-δ ethylenic alcohols, with different mercuric salts under different conditions. By “in situ” reduction, or by direct reduction of isolated mercuric compounds, we obtain, in some cases, diastereoisomers with different relative yields.  相似文献   
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