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1.
D. Ya. Tsvankin V. S. Papkov V. P. Zhukov Yu. K. Godovsky V. S. Svistunov A. A. Zhdanov 《Journal of polymer science. Part A, Polymer chemistry》1985,23(4):1043-1056
The structure changes accompanying phase transitions in poly(diethylsiloxane) (PDES) have been studied by WAXS and SAXS techniques using oriented and isotropic samples. PDES may exist in two low-temperature modifications (the monoclinic α1-form and presumably the “tetragonal” β1-form) and two high-temperature modifications (the monoclinic α2-form and the “tetragonal” β2-form). In linear PDES the crystal - crystal transitions α1–α2 and β1–β2 occur near 214 and 206 K, respectively. At higher temperatures α2 (280 K) and β2 (290 K) forms transform into the mesomorphic phase αm that gradually melts at 280–300 K giving an amorphous phase. According to x-ray and density data, αm phase is also characterized by monoclinic structure slightly different from hexagonal packing. 相似文献
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N. I. Shvets V. T. Minakov V. S. Papkov M. I. Buzin L. Yu. Bad’ina A. A. Shimkin 《Russian Journal of Applied Chemistry》2014,87(6):796-802
The possibility of preparing polymeric ceramic-forming precursors from polycarbosilane and oligosilazane was examined. Oligosilazane as a component of polycarbosilane formulations acts as a curing agent, ensuring curing at 150–300°C in the absence of oxygen and modifier. Pyrolysis of the cross-linked copolymer in argon yields an inorganic matrix whose yield is 1.3 times higher than that of pyrolyzates of the starting components. The major phase of the ceramic products obtained, according to the results of X-ray diffraction and chemical analyses, is X-ray amorphous silicon carbide. The ceramic obtained is highly resistant to thermal oxidation (up to 1400°C). The composition of the ceramic and the heat resistance and service characteristics of ceramic-matrix composite materials prepared on its basis using the “polymer technology” can be controlled by varying the ratio of the initial oligomers. 相似文献
4.
L. V. Filimonova L. I. Makarova A. A. Voronina T. V. Strelkova I. G. Barakovskaya B. G. Zavin A. J. Pertsin V. S. Papkov 《Polymer Science Series B》2013,55(5-6):266-270
Oligo(diethylsiloxane diols) carrying β-oxyethoxymethyl terminal groups are synthesized for the first time by the cationic polymerization of hexaethylcyclotrisiloxane in the presence of bis(β-oxyethoxymethyl)tetramethyldisiloxane with the use of sulfuric acid or the cationite KU-23 as a catalyst. It is shown that, along with oligo(diethylsiloxane diols), the products of rearrangement of diethylsiloxane chains, such as octaethylcyclotetrasiloxane and higher cycles, are formed. The reaction of dipotassium salts of oligo(diethylsiloxane diols) with chlorosilanes of the formula ClSi(CH3)2CH2O(CH2)2OCOCH3 yields acetoxy-terminated oligomers that contain octaethylcyclotetrasiloxane and higher cycles as well. 相似文献
5.
Flexible linear polysiloxanes with inorganic backbones such as poly(diethylsiloxane) and poly-(dipropylsiloxane) contain no traditional mesogenic groups neither in the main chain nor in side chains and, nevertheless, they are able to form thermotropic mesophases. Recent developments in the study of thermodynamics, kinetics, structure and morphology of these mesophase polymers are considered. The temperature interval of existence of the mesophase is strongly dependent on the length of side radicals and molecular weight. These dependences are examined in detail. X-ray structure and the optical textures seen in the polarizing microscope are discussed. It is shown that large mesophase lamellae represent a very characteristic feature of the morphology of poly(diethylsiloxane). The linear growth rate of the lamellae and the overall calorimetric kinetics of the mesophase formation have been studied at various temperatures and the results obtained have been analyzed using the Avrami equation and the kinetic theory of the linear growth. As a result of the kinetic analysis two-dimensional growth has been suggested in accordance with the microscopic observation. The formation of the mesophase in slightly crosslinked poly(diethylsiloxane) samples can be initiated by stretching. The stress-strain and thermomechanic (deformation calorimetry data) behaviour of such samples is briefly discussed. 相似文献
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L. A. Pavlova M. P. Tsyurupa M. A. Papkov V. A. Davankov 《Russian Journal of Applied Chemistry》2010,83(5):885-889
Synthesis and properties of hyper-cross-linked polymer networks prepared by radical polymerization of commercial divinylbenzene
in oxylene, a good solvent and a powerful telogen, are reported. The permeability of hyper-cross-linked networks is evaluated
by adsorption of bioactive molecules significantly differing in size. High sorption capacity for Cephalosporin C makes the
polymers prepared promising for pharmacology and biotechnology. 相似文献
8.
Ozerov OV Guo C Papkov VA Foxman BM 《Journal of the American Chemical Society》2004,126(15):4792-4793
An investigation of room-temperature oxidative addition of N-C and N-H bonds to RhI and IrI in solution and in the solid state is presented. The rigid, product-adapted framework of the pincer bis(ortho-phosphinoaryl)amine (PNP) ligand may contribute to the ease of the N-C and N-H cleavage. The migration of Me from N of the coordinated amine moiety to Rh proceeds with near-zero entropy of activation in solution. In the solid state, this transformation is a crystal-to-crystal reaction, transforming only one of the two independent molecules of (PN(Me)P)RhCl into (PNP)Rh(Me)Cl. 相似文献
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V. S. Papkov V. S. Svistunov Yu. K. Godovsky A. A. Zhdanov 《Journal of Polymer Science.Polymer Physics》1987,25(9):1859-1884
Optical and calorimetric studies of the kinetics of mesophase formation and crystallization in poly(diethylsiloxane) have been conducted. The mesomorphic phase is found to grow from the isotropic melt in the form of lamellar domains about 2 μm thick in the temperature range 293–307 K. According to birefringence data, macromolecules in the mesomorphic lamellae are perpendicular to the end faces. The kinetics of mesophase formation obey the Avrami equation with the morphological parameter n close to 2 (it is equal to 1.75 ± 0.05), which corresponds to the two-dimensional growth of the mesomorphic phase from athermal nuclei. The limiting conversion of the isotropic melt was shown to be temperature-dependent. This is likely to be connected with a change in the number of nuclei with temperature. The crystallization of polymer from the mesomorphic state occurs with retention of the optical texture of the sample. The process proceeds not as a sporadic crystallization of individual mesomorphic lamellae but as a growth of the nucleated crystalline regions via a consecutive incorporation of adjacent crystallizing lamellae. 相似文献