Kinetic scheme and rate constants for methyl methacrylate synthesis occurring via the radical–coordination mechanism

Two kinetic schemes of the bulk radical–coordination polymerization of methyl methacrylate initiated by the benzoyl peroxide–ferrocene system are considered from the standpoint of formal kinetics. The most likely kinetic scheme is the one that includes the reactions characteristic of classical radical polymerization and, additionally, reactions of controlled radical polymerization proceeding via the Organometallic Mediated Radical Polymerization mechanism, a reaction generating a coordination active site, and a chain propagation reaction in the coordination sphere of the metal. The temperature dependences of the rate constants for the reactions of this kinetic scheme at temperatures typical of commercial poly(methyl methacrylate) production (313–353 K) have been determined by solving the inverse kinetic problem.     

Antitumor activity of carboplatin in the composition of a copolymer of lactic and glycolic acids

Polymer particles containing carboplatin (CPt) were developed by the inclusion of this antitumor agent in a copolymer of lactic and glycolic acids (PLGA-COOH 50/50). The polymer particles were found to have a spherical form with an average diameter not exceeding 200 nm, the ζ-potential is equal to–32.2±1 mV. The CPt-loaded polymer particles possess a cytotoxic activity against human small cell and non-small cell lung carcinoma (lines H69 and A549), as well as against mouse mammary adenocarcinoma (line Ca755). The results of the in vivo studies carried out on female mice of line C₅₇Bl/6 with inoculated mouse melanoma of line B16 showed increasing of lifespan of the animals and inhibition of tumor growth for groups treated with the polymer particles, as compared to the animals treated with the drug substance CPt.     

Photoluminescence in germanium with a quasi-equilibrium dislocation structure

The dislocation-related photoluminescence of n-Ge single crystals with a quasi-equilibrium structure of 60° dislocations is investigated at a temperature of 4.2 K. It is shown that the dislocation-related photoluminescence spectra are described by a set involving from 8 to 13 Gaussian lines with a width of less than 15 meV. With due regard for the data available in the literature, the Gaussian lines with maxima at energies in the range 0.47 < E _m ≤ 0.55 eV are assigned to the emission of 90° Shockley partial dislocations involved in quasiequilibrium segments of 60° dislocations with different values of the stacking fault width Δ (Δ = Δ₀, Δ < Δ₀, and Δ > Δ₀). It is revealed that the d8 line at the energy E _m = 0.513 eV, which corresponds to the emission of straight segments with the equilibrium stacking fault width Δ₀, dominates in the photoluminescence spectra only at dislocation densities N _D < 10⁶ cm^?2. As the dislocation density N _D increases, the intensity of the d8 line decreases with the d7 line (E _m ≈ 0.507 eV) initially and the d7 and d6 lines (E _m ≈ 0.501 eV) then becoming dominant in the photoluminescence spectrum. The d7 and d6 lines are attributed to the emission of segments with stacking fault widths Δ < Δ₀. Possible factors responsible for the formation of stacking faults with particular widths Δ ≠ Δ₀ for quasi-equilibrium dislocations are discussed.     

Energy threshold of Cs-induced chemisorption of oxygen on a GaAs(Cs,O) surface

The probability of Cs-induced chemisorption of oxygen on a p-GaAs(Cs, O) surface is experimentally shown to be close to unity only when the work function does not exceed ～3.1 ± 0.1 eV. The measured adsorption energy threshold likely corresponds to the energy of the unoccupied level of the antibonding 2π* orbital of the O₂ molecule in the preadsorption state on the semiconductor surface.     

Origin of Degradation of the CaF2/BaF2 Buffer Layers on Si(111)

Doklady Physics - The growth temperature dependences of the capacitance–voltage characteristics and chemical stability of the CaF2/BaF2 buffer layers formed on Si by molecular beam epitaxy...     

Radiotomographic observations of the ionosphere electron density at the Spitsbergen Archipelago-Kola Peninsula-Karelia meridian

The first results on the reconstruction of two-dimensional ionosphere electron density by the method of satellite tomography in the area extended for about 1700 km from the subauroral ionosphere (Karelia) to the nearpolar cap zone (northwest of the Spitsbergen Archipelago) are analyzed. This experiment is unique in that the satellite-receiving apparatus was placed on a research ship in the Barents Sea, which separates the Kola Peninsula and the Spitsbergen Archipelago. The results obtained are evidence of a complex ionospheric structure in this region even under the quiet geophysical conditions of sunlight irradiation.     

Catalytic properties of zirconium phosphate and double phosphates of zirconium and alkali metals with a NaZr2(PO4)3 structure

Zirconium orthophosphate Zr₃(PO₄)₄ and double phosphates of zirconium and alkali metals AZr₂(PO₄)₃ (A = Na, K, Rb, Cs) with a NaZr₂(PO₄)₃ structure were synthesized and characterized by X-ray diffraction and electron microprobe analyses and capillary condensation of nitrogen. The catalytic properties of the phosphates in the dehydration of methanol were studied.