Structure of the polymer chain of poly(1,3-pentadiene) synthesized using a stereospecific catalytic system

Russian Chemical Bulletin - The structure of polymer chain of poly(1,3-pentadiene) synthesized via a stereospecific polymerization catalyzed by a system based on neodymium trichloride was...     

Alumina ceramics for stomatologic purposes

An alumoxide ceramic implant doped with magnesium oxide is developed and its structure and physicochemical and mechanical properties are examined. Medicobiologic investigations of the implant are also carried out. The implant Alumag-1 is recommended for clinical testing.Translated from Mekhanika Kompozitnykh Materialov, Vol. 5, No. 2, pp. 253–260, March–April, 1999.     

Investigation of the structure of nanocrystalline refractory oxides by X-ray diffraction,electron microscopy,and atomic force microscopy

The structures of nanocrystalline fibrous powders of refractory oxides have been investigated by different methods: determination of coherent-scattering regions, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic-force microscopy (AFM). The sizes of nanograins of different crystalline phases of refractory metal oxides have been determined during the formation of these nanograins and the dynamics of their growth during heat treatment in the temperature range 600–1600°C has been studied. The data on the structure of nanocrystalline refractory oxide powders, obtained by different methods, are in good agreement. According to the data on coherent-scattering regions, the sizes of the ZrO₂ (Y₂O₃) and Al₂O₃ grains formed are in the range 4–6 nm, and the particle sizes determined according to the TEM and AFM data are in the ranges 5–7 and 2–10 nm, respectively. SEM analysis made it possible to investigate the dynamics of nanoparticle growth at temperatures above 1000°C and establish the limiting temperatures of their consolidation in fibers.

     

Polymerization of penta-1,3-diene using cationic catalytic systems based on organoaluminum compounds

Russian Chemical Bulletin - Cationic polymerization of penta-1,3-diene with catalytic systems based on organoaluminum compounds (AlEtCl2, AlEt2Cl, and AlEt3) in combination with isopropyl chloride...     

Poly(methylene green) employed as molecularly imprinted polymer matrix for electrochemical sensing

This paper describes the development of a molecularly imprinted polymer (MIP) for theophylline that can be used for electrochemical sensing. Theophylline is a commonly used medication for the treatment of asthma. Due to its very narrow therapeutic index, it may have toxic and potentially fatal effects on the individual. Electrochemical detection of theophylline is difficult, because its molecular structure and standard reduction potential are very similar to that of caffeine. A new method for fabricating molecularly imprinted polymers is proposed utilizing methylene green. Poly(methylene green)(PMG), prepared by electropolymerization of an azine, methylene green, was imprinted for theophylline. PMG-based MIP-coated electrodes showed sensitivity towards the presence of the imprint molecule in solutions, as well as selectivity for the imprint over the interferent molecule caffeine. The PMG-based MIP-coated electrode described in this paper had an improved selectivity factor and reproducibility compared to other theophylline-imprinted MIP-coated electrodes in literature.     

Hydrolytic degradation of poly[(4,4′-oxydiphenylene)pyromellitic amido acid] in concentrated sulphuric acid and in dimethylformamide via hydrodynamic investigations

Translational diffusion and viscosity measurements were performed for poly[(4,4′-oxydiphenylene)pyromellitic amido acid] in DMF, LiCl/DMF, and 96% H₂SO₄ solutions to characterise the rate of the polymer degradation in 96% H₂SO₄ in comparison with its relative stability in organic solutions. The hydrodynamic data were obtained in different stages of hydrolytic polymer degradation at various temperatures from 20 to 80 °C. The mechanism of the degradation is discussed as well as the possibility of molecular investigations of the polymer under conditions of quasi-stable solution.     

Fibrous Filler-Matrix Interaction in Oxide Composites

The interaction between a fibrous alumina filler and a hydrated zirconia matrix during the fabrication of ceramic composites is studied. The influence of the crystal structure and porosity of the filler on the properties of the ZrO₂-Al₂O₃ composite material is investigated. It is found that, as a result of addition of alumina fibers of cubic and monoclinic structures (- and -phases), the ZrO₂ hydrogel interacts with fibers and solid ZrO₂ solutions of tetragonal structure are formed. These solutions exist over the range of 600 to 1200°C and, at annealing above 1200°C, due to crystallographic transitions the of - and -phases, they break down, namely Al₂O₃ transforms into -corundum and ZrO₂ into a monoclinic modification. However, the material does not fail and a stable porous ceramic composite is formed. To manufacture a composite with improved mechanical characteristics, fibrous alumina fillers with the structure of -corundum must be used.     

Structure and Properties of Nanocrystalline Oxide Powders

The crystalline and porous structure of superfine powders and fibers made of alumina and zirconia doped with yttria is investigated. The particle sizes were determined by the methods of coherent dispersion and scanning transmission electron microscopy. Based on data on the sizes of crystallites of the metal oxides, which were obtained by different methods, it is found that crystalline transformations of the oxides lead to dispersion of the materials. The structural transformations of the superfine oxides are accompanied by changes in crystallite sizes and in the character and size of pores. The laws established allow one to purposefully control the process of producing nanostructured oxide powders and fibers, which can be utilized as active fillers for composite materials based on various matrices. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 6, pp. 831–840, November–December, 2005.     

Alumina ceramics for stomatologic purposes

An alumoxide ceramic implant doped with magnesium oxide is developed and its structure and physicochemical and mechanical properties are examined. Medicobiologic investigations of the implant are also carried out. The implant Alumag-1 is recommended for clinical testing.