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371.
Giorgio Montaudo Concetto Puglisi Corrado Berti Elisabetta Marianucci Francesco Pilati 《Journal of polymer science. Part A, Polymer chemistry》1989,27(7):2277-2290
The thermal degradation of three aliphatic polythiocarbonates was investigated by direct pyrolysis in the ion source of a mass spectrometer operating both in electron and chemical ionization modes. The overall evidence indicates that these polymers start decomposing at about 250–280°C by an end-biting process initiating from the SH end-groups, which produces a mixture of cyclic sulfides, disulfides, and dithiocarbonates. Another decomposition step is observed at higher temperature (ca. 350–370°C), producing essentially the same compounds evolved in the first stage, but with significant differences in their relative abundances. An intramolecular exchange (back-biting) process is believed to be responsible for the second thermal decomposition stage 相似文献
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374.
Umberto Bianchi Carla Cuniberti Enrico Pedemonte Corrado Rossi 《Journal of Polymer Science.Polymer Physics》1969,7(5):855-866
Heats of solution (ΔHexp) in solvents of increasing thermodynamic power have been measured for four polymers: polystyrene (PS), poly(vinyl acetate) (PVAc), polyisobutylene (PIB) and polydimethylsiloxane (PDMS). After subtraction from ΔHexp of an interaction term (calculated by the Hildebrand treatment based on solubility parameters) and the excess volume term, the quantity remaining is interpreted as the conformational energy contribution (ΔUconf) to the heat of solution. ΔUconf appears to correlate well with some basic conformational properties of the chain, such as the sign of the temperature coefficient of unperturbed dimensions derived from solution properties, and shows a monotonic behavior with α, the expansion coefficient of the polymer coil in the final solution. Numerical values of ΔUconf, at least for those cases in which polymer solubility parameters are known with some certainty, are much larger than those evaluated from rubber elasticity experiments (through the experimentally accessible value of the energy component of the force of retraction im simple elongation). 相似文献
375.
Guido Cimino Salvatore De Rosa Salvatore De Stefano Aldo Spinella Guido Sodano 《Tetrahedron letters》1984,25(27):2925-2928
The yellow zoochrome of the sponge , which blackens when exposed to the air, has been isolated and its structure established as 3,5,8-trihydroxy-4-quinolone. The pigment is easily oxidized to an unstable blue quinone which quickly gives rise to an unsoluble black material. 相似文献
376.
Paolesse R Di Natale C Nardis S Macagnano A D'Amico A Pinalli R Dalcanale E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(21):5388-5395
The sensing properties of functionalized cavitands have been studied by thin-film coating TMSR chemical sensors and by measuring their responses towards model analytes. We studied the relationship between the sensor performance, in terms of sensitivity and selectivity, and the molecular recognition properties of the cavitands. The Langmuir-like shape of the adsorption isotherm, obtained in the case of short-chain alcohols, demonstrated that selective binding can be achieved by the synergistic interactions of the cavity and the bridging PO(in) groups. In the absence of these substituents, the peripheral alkyl chains necessary for the formation of highly permeable thin films attenuate the cavity effect because of nonspecific dispersion interactions. This completely overrides the response originating from molecular recognition. The same effect is observed when the PO groups are oriented outward from the cavity. The use of multivariate chemometrics and the study of the correlations between sensors sensitivity and analyte properties provided further evidence of molecular recognition phenomena, whose intensity is enhanced by the permanent free volume created by the rigid cavity surrounding the PO(in) group. 相似文献
377.
Summary Seven new copper(II)pyridoxal salicyloylhydrazone complexes have been prepared and characterized by vibrational and electronic spectra and magnetic measurements. The u.v. absorption band maxima are compared with those of metal chelates of Schiff bases obtained from condensation of pyridoxal with amines or amino acids. 相似文献
378.
This review details ion chromatography developments and related applications, mainly in the field of environmental analysis, gained by the evolution in the science and technology for new stationary phases. Unconventional approaches to ion chromatographic separations are also outlined. 相似文献
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Zirconium (6–121 μg) is determined with xylenol orange after liquid-liquid extraction by tri-n-butylacetohydroxamic acid (TBAH) from 6 M hydrochloric acid. Under optimal conditions (primarily, 1 1:1.5 ratio of TBAH to xylenol orange, addition of acetic acid, and measurement at 545 nm), the calibration is linear with a molar absorptivity of 34 650 l mol?1 cm?1. Ions which are not extracted by TBAH or donot form coloured complexes do not interfere; these include uranium and rare-earth elements. Hafnium interferes; interference from thorium is avoided by a preliminary extraction of zirconium with tri-n-octylamine. 相似文献