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251.
Aromatic bisorthoesters were found to be good polymer intermediates and could be condensed with aromatic tetramines under mild conditions, in DMSO at 100°C in a relatively short reaction time to give polybenzimidazoles. The hexapropyl orthoesters of terephthalic and isophthalic acid were the preferred aromatic orthoesters because they were relatively easily purified by vacuum distillation to polymer grade intermediates, since they are liquids. Higher orthoesters distill even under good vacuum near or above the decomposition temperature of the orthoester group. Hexaethyl orthooxalate was also used and is a very useful and stable derivative of oxalic acid, which can be used for condensation reactions. These three orthoesters were used for condensations with 3,3′,4,4′-tetraaminobiphenyl, 1,2,3,4-tetraaminobenzene, 3,3′,4,4′-tetraaminobiphenyl ether, and 3,3′,4,4′-tetraaminobenzophenone. All polybenzimidazoles were obtained in high to quantitative yields and with varying molecular weights (ηinh = 0.1?0.8 dl/g), which in some cases were in the fiber forming range. 相似文献
252.
Conditions for the formation of rare earth element (Y, La–Lu) 3-methylglutarates were studied and their quantitative composition
and solubilities in water at 293 K were determined (10–2 mol dm–3). The IR spectra of the prepared complexes with general formula Ln2(C6H8O4)3
nH2O (n=3–8) were recorded and their thermal decomposition in the air were investigated. During heating the hydrated 3-methylglutarates
are dehydrated in one step and next anhydrous complexes decompose to oxides Ln2O3 with intermediate formation Ln2O2CO3 (Y, La, Nd–Gd) or directly to the oxides, Ln2O3, CeO2, Pr6O11 and Tb4O7 (Ce, Pr, Tb–Lu).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
253.
The coulometric electrolytic principle is utilized for the measurement of moisture sorbed on sintered thorium dioxide. Moisture is removed from the sample by heating and is swept by dry argon gas through a hygrometer. The resulting hygrometer output is converted into frequency pulses and counted cumulatively. The instrument is calibrated by use of standard hydrated chemicals. The number of counts/mu;g of water obtained from standards compares favourably with the theoretical number of counts/mu;g calculated from performance specifications of the components employed. The error is <5% for 1-350mu;g of water. A high sensitivity and low operating blank recommends application of this method to materials other than thorium dioxide, having very low moisture contents. 相似文献
254.
255.
256.
Conclusions In our view, the material examined in the present review indicates that, in spite of the appearance of more accurate methods of calculating the electronic structure and the increasing possibilities provided for their realization for fairly complex systems, the applied value of simple semiempirical methods, in particular the CNDO method, is far from exhausted. In the near future, semiempirical calculations will probably provide the chief means of studying the electronic structures of complex molecules, by becoming accessible to an increasing circle of chemists.Leningrad State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 17, No. 3, pp. 549–577, May–June, 1976. 相似文献
257.
1. | The structures and stability constants of outer-sphere adducts of Co(HBpz3)2 with aromatic nitro compounds have been determined. |
2. | The process of outer-sphere solvation of Co(HBpz3)2 has been shown to lie outside the framework of a simple donor-acceptor model for adduct formation. |
258.
The fast formation of cations of benzophenone, biphenyl, naphthalene, anthracene and phenanthrene in liquid cyclohexane was studied by nanosecond pulse radiolysis. Rate constants between 2.3 × 1010 M?1 s?1 (for naphthalene) and not below 2.5 × 1012 M?1 s?1 (for benzophenone) were derived and compared with the corresponding rate constants for anion formation. 相似文献
259.
260.
M. Ghafar A. Abdul-Hadi O. Alhassanieh 《Journal of Radioanalytical and Nuclear Chemistry》2002,254(1):159-163
The distribution of U, Th, Am, Eu, Cs, Sr and Ra in a solid-aqueous system, natural phosphate in contact with groundwater was investigated using g- and a-spectroscopy. The effect of contact time, pH, particle size of the solid phase, and the concentration of a concurrent element Ca, were studied. The results show that more than 98% of the actinide elements and europium are adsorbed by the solid phase under all conditions. The fission products Cs and Sr have different behaviors, depending on the experiment conditions. The behavior of Ra is closer to the actinides than to the fission products. There are small differences between the behaviors of the actinide elements, which can be interpreted by migration mechanism from the aqueous to the solid phase, i.e., adsorption or precipitation. 相似文献