Investigation into the dielectric relaxation of vinylidene fluoride copolymers with hexafluoropropylene

Four relaxation processes and one ferroelectric-paraelectric phase transition are revealed in vinylidene fluoride-hexafluoropropylene copolymers with different ratios of the components in the temperature range from ?100 to 150°C. The relaxation process occurring at the lowest temperature is associated with the local mobility of the chains, whereas the relaxation process at a higher temperature is due to micro-Brownian motion of segments in the amorphous phase in the glass transition range. A smeared relaxor phase transition from the polar modification of the α phase of vinylidene fluoride units to the paraelectric phase is observed in the temperature range 50–70°C. At higher temperatures, there occurs an intensive relaxation process that can be attributed to space-charge relaxation or manifestation of the normal relaxation mode.     

Influence of cobalt(III) dimethyldithiocarbamate complexes on styrene polymerization initiated by tert-butyl perbenzoate

Kinetic features of radical polymerization of styrene initiated by tert-butyl perbenzoate in the presence of tris(N,N-dimethyldithiocarbamato)cobalt(III) (CoL₃) and its adduct with iodine (CoL₃ · 2I₂) were studied. The optimal concentration ratios of the activators and tert-butyl perbenzoate, providing fast styrene polymerization at 338–368 K, were determined.     

Hydrophobicity and thermal stability of fluorinated pentaerythritol esters

Wetting angles and limits of thermal stability of esters derived from pentaerythritol and perfluoro-, ω-chloropolyfluoro-, and perfluoropolyethercarboxylic acids were studied.     

Conformational implications of some nucleotide sequences

The conformational properties of some nucleotide sequences result in their ability to bind specifically some ligands or tobe recognized by specific proteins. In order to investigate the dependence of conformational behavior of the DNA duplex on nucleotide sequence, we analyzed the interaction energy of nucleic acid bases as a function of conformational parameters and base sequence. Extended regions of minimum energy values were found for different sequences. Although these regions (valleys) largely overlap, each one shows specificity for a particular sequence. This suggests that a specific pathway of changes in conformational parameters exists for each sequence. the changes may be accompanied by considerable shifts (2–3 Å) of the atom positions and an only slight variation (1–2 kcal/mol) of energy. Even small shifts in other directions can cause a drastic energy increase. For some nucleotide sequences, the energetically preferable conformations are the B-like ones (e.g., ApA, TpA), whereas for others the A-like ones are preferable (e.g., GpG, ApT). IN general, Pyr-Pur sequences have a tendency to a larger τ and smaller H and D than Pur-Pyr sequences. A large body of experimental data on nucleic acid structure in fibers and in solutions can be explained by results obtained.     

Influence of the energy and velocity spread in the electron beam on the starting conditions and efficiency of a gyrotron

We study theoretically the influence of the spread of initial energies and velocities in the electron beam on the starting conditions and efficiency of a gyrotron. We compare various analytical and numerical models and the results of experimental studies of gyrotrons in which the interaction takes place at the first and second harmonics of the cyclotron frequency. The aftercavity interaction of the electron beam with the high-frequency field in the output waveguide transition is taken into account. The influence of the energy spread on the recuperation efficiency is estimated. Permissible spreads of the initial energies and electron velocities are determined. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 2, pp. 121–133, February 2006.     

Synthesis and conformational study of 1,2,3,4,5,6,7,8-octahydro-1,6-naphthiridines

A new class of endocyclic enamines, 1,6-disubstituted 1,2,3,4,5,6,7,8-octahydro-1,6-naphthiridines, was synthesized from 4-piperidone imines by successive subjecting the latter to lithiation with lithium diethylamide, to alkylation with 1-bromo-3-chloropropane, and to intramolecular cyclization. All stages were carried out as a unique process without isolation of the intermediate compounds. A thorough optimization of the process conditions, workup, and product storage was carried out. The conformational study of 1,6-disubstituted 1,2,3,4,5,6,7,8-octahydro-1,6-naphthiridines was performed.     

An unusual transformation of perfluorinated 1- and 3-phenylpropenes to polyfluorochloroindanes by the action of AlCl3

The reaction of perfluorinated 1- and 3-phenylpropenes with AlCl₃ gives polyfluorochloroindanes as the result of an intramolecular cyclization, apparently, by an electrophilic pathway.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2854–2857, December, 1989.