Effect of iodine sorption on the free volume of polycarbonate

 The effect of iodine sorption on the free volume of polycarbonate is investigated by Positron Annihilation Lifetime method. The observed results are interpreted in terms of the Charge Transfer Complex formation and precipitation of iodine at the initial and final stages of sorption, respectively. At higher levels of sorption, changes in the second lifetime and its intensity seem to suggest a conformational transformation, probably due to the net change in the amorphous-crystalline boundary regions of the polymer matrix. The free volume cavities have been predominantly occupied by I^- ₃ species and the diffusion process obeys Fick’s law. An exponential type correlation has been observed between fractional free volume and the diffusion coefficient. Received: 13 June 1996/Accepted: 20 September 1996     

A poincaré-bendixson theorem for analytic families of vector fields

We provide a characterization of the limit periodic sets for analytic families of vector fields under the hypothesis that the first jet is non-vanishing at any singular point. Also, applying the family desingularization method, we reduce the complexity of some of these sets.     

Influence of the sulfonate countercation on the thermal stability of nafion perfluorosulfonate membranes

We report a strong dependence of the thermal stability of Nafion® perfluorosulfonate ionomer on the nature of the counterion associated with the fixed sulfonate site. These results were obtained using thermal gravimetric analysis on a series of alkali metal and alkyl ammonium cation-exchanged Nafion films. We have found that the temperature of decomposition of Nafion is inversely dependent on the size of the exchanged cation; i.e., Nafion films show improved thermal stability as the size of the counter cation decreases. We attribute this inverse relationship of thermal stability with counterion size to an initial decomposition reaction which is strongly influenced by the strength of the sulfonate-coun-terion interaction. © 1993 John Wiley & Sons, Inc.     

Increasing the accuracy of eigenvalue computation in the spectral problem

A simple method is proposed for increasing the accuracy of computation of the eigenvalues of elliptic operators, which does not require high-order accurate schemes.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 63, pp. 63–68, 1987.     

2-Carbethoxymethyl-4H-3,1-benzoxazin-4-one. 4. Reaction with anilines

In a solution of DMF, 2-carbethoxymethyl-4H-3,1-benzoxazin-4-one reacts with primarily aromatic amines basically with the formation of the corresponding 2-carbethoxymetlzyl-3-arylquinazolin-4(3H)-ones. Possible mechanisms of these chemical transformations are reported and discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 225–228, February, 1994. Original article submitted June 28, 1993.     

Synthesis and ring-chain isomerism of acid chlorides and amides of 2-(2-pyridyl and 2-quinolylcarbonyl) benzoic acids

The reaction of 2-(2 pyridytcarbonyl)benzoic acid with thionyl chloride affords an unexpected product of the intramolecular acylation of the pyridine nitrogen atom, namely, 6,11-dioxo-6,11-dihydrobenzo[blquinotizinium chloride. At the same time, 2-(2-quinotylcarbonyl)benzoic acid forms the expected cyclic acid chloride, namely, 3-(2-gitinotyl)-3-chlorophthalide in this reaction. Both compounds acylate ammonia and primary amines, including those with bulky alkyl groups (tert-butyl, 1-adamantyl, and 1,1,3,3-tetramethylbutyl) with the formation of 2-R-3-hydroxy-3-(2pyridyl- or 2-quinolyl)isoindolines. The protonation of the pyridine nitrogen atom of N-(1,1,3,3-tetramethylbutyl)-2-(2pyridylcarbonyl)benzamide, obtained in the open amide form, is accompanied by the closing of the isoindotinone ring; the deprotonation is accompanied by ring opening.Riga Technical University, Riga LV-1048. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 499–504, April, 1994. Original article submitted March 17, 1994.     

Electrohydraulic effect in heterodisperse water-plant systems. II. Chemical nature of the suspended particles

On the basis of the results of acid hydrolysis, chromatographic analysis of the hydrolysates, and a study of IR spectra, it has been established that the suspended particles liberated under the action of electrohydraulic shocks on heterodisperse water—plant systems consist of small fragments of the lignocarbohydrate complex of the plant tissue.     

Electron-impact mass spectra of natural phenylethanoids

The electron-impact mass spectra of a number of phenylpropanoids and iridoid glycosides containing a phenylethanoid fragment in their structure have been studied. This has revealed features of the formation of fragments of 4-hydroxyphenylethyl and 3,4-dihydroxyphenylethyl alcohols and also of fragments of phenylethylamine and indolylethylamine derivatives present in the structures of the compounds investigated.