Condensation of all-cis-tetraphenylcyclotetrasiloxanetetraol in ammonia: new method for preparation of ladder-like polyphenylsilsesquioxanes

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Synthesis and characterization of oxidized cellulose

Samples of oxidized cellulose (OC) with various carboxyl contents and degrees of crystallinity were obtained by the oxidation of native and mercerized cellulose with a solution of nitrogen(IV) oxide in CCl₄. A detailed characterization of these OC samples was performed. The effect of oxidation conditions (concentration of N₂O₄ in the solution and oxidation time) and starting cellulose material on OC characteristics (carboxyl, carbonyl and nitrogen content, degree of crystallinity and polymerization, surface area and swelling, and acidic properties) was investigated. Reactivity in the oxidation process was higher in mercerized cellulose than in native cellulose. The action of dilute solutions (10–15%) of N₂O₄ did not affect the degree of crystallinity of cellulose samples. Under these conditions, the oxidation took place mainly in amorphous regions and on the surface of crystallites. Oxidation in a concentrated (40%) N₂O₄ solution led to the destruction of crystallites, which increased the surface area and swelling of cellulose in water. The surface area and the swelling of OC samples increased with a decrease in the index of crystallinity. The acidic properties of OC were shown to increase with an increase of swelling in water. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4785–4791, 2004     

Using the method of integral relationships to determine the seepage parameters of a layer

We consider nonlinear seepage with an initial pressure gradient in a region without stagnant zones. An algorithm based on the method of integral relationships is proposed for the determination of an auxiliary function defined as the square root of the permeability coefficient of the layer. The advantage of this method is that it reduces the problem to a form which can be solved by standard computer subprograms. Applications of the proposed approach are described.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 55, pp. 87–92, 1985.     

Thermal degradation of composites of poly(methyl methacrylate) with alkoxysilane hydrolyzates

Organic-inorganic composites of poly(methyl methacrylate) with alkoxysilane hydrolyzates form transparent films. Their thermal and oxidative thermal degradation were studied by differential scanning calorimetry and thermogravimetric analysis.     

Effect of 2,2,6,6-tetramethyl-1-piperidinyloxy nitroxide substituent on kinetic parameters of pseudoliving polymerization

The main kinetic and thermodynamic parameters of the pseudoliving radical polymerization of styrene mediated by 4-linoleamido-2,2,6,6-tetramethyl-1-piperidinyloxy have been studied. It has been shown that the introduction of the said substituent into nitroxide leads to a marked reduction in the rate constant of reinitiation that is compensated for by the simultaneous reduction in the rate constant of reversible termination. As a result, the rate of pseudoliving polymerization, the rate of molecular mass growth, and the polydispersity of the polymer appear to be practically the same for processes mediated by both unsubstituted and substituted nitroxides.     

Free-radical polymerization of N-vinylpyrrolidone under the conditions of secondary inhibition

The polymerization of N-vinylpyrrolidone has been studied in the presence of the stable radical 2,2,6,6-tetramethyl-1-piperidinyloxy. It has been shown that at 120°C the polymerization proceeds via the irreversible inhibition mechanism, while, at 60°C, secondary inhibition occurs in the system during the postinduction period. This effect may be used for regulation of the molecular-mass characteristics of polymers.     

Optimization of Oscillations of Mechanical Systems

Doklady Mathematics - The problem of controlling oscillations near the equilibrium position of a scleronomic mechanical system with several degrees of freedom is solved. One degree of freedom is...     

Kinetic isotope effect in proton exchange processes between methanol and water in inert solvents

The kinetic isotope effect in proton exchange between methanol and water in CCl₄ solution was studied by¹H and²H NMR and kinetic IR spectroscopy. The exchange rate increases in the series CD₃OH+H₂O3OD+H₂O3OD+D₂O. It has been concluded that the limiting step of the reaction involves the formation of an H-bonded cyclic intermediate.

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¹H ²H - CCl₄. , CD₃OH+H₂O3OD+H₂O3OD+D₂O. , - -.

     

Indole derivatives

The behavior of some 3-nitrovinyl indoles in their reactions with nitrogen-containing nucleophilic reagents is examined. It is shown that hydroxylamine, phenylhydrazine, hydrazine, and semicarbazide react with 3--nitrovinyl indole to give the corresponding oxime, phenylhydrazone, azine, and semicarbazone of indole-3-aldehyde, possibly by decomposition of intermediates formed by the addition of the nucleophilic reagents to the nitrovinyl indole. 3--Nitropropenyl indole and N-methyl-3--nitrovinyl indole react similarly. Only the addition products of phenylhydrazine with N-acetyl-3-nitrovinyl indole and N-acetyl-3--nitropropenyl indole are stable. The reaction conditions and constants of the compounds prepared are given, and explanations are offered for the results obtained.For part XXXV, see [14].