Том 53, № 4 (2019)

Numerical and analytical solutions of kinetic equations and the relevant equations for the moments of distribution of macroradicals and oligomers during radical chain polymerization are presented. It has been shown that the initial chain growth occurs in the ballistic mode involving first-generation primary radicals. The chain transfer in which a macroradical, reacting with a solvent, forms an oligomer and the primary radical of the next generation, causes a transition from the ballistic to the diffusion mode in which distributions of chains of different generations are mixed. Time-dependent distributions have been found for chain propagation and transfer rate constants independent of chain length.

The kinetics of autoradiolytic degradation of the radiopharmaceutical drug 2-[¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) in an air-saturated normal saline solution with initial activity concentrations of 1 and 2 GBq/mL has been studied. It has been established that the only radioactive product of radiation-induced transformations of [¹⁸F]FDG is [¹⁸F]fluoride, whose contribution in the total activity of the radiopharmaceutical increases with storage. It has been shown that an increase in the initial activity concentration of the radiopharmaceutical or a decrease in the concentration of ethanol in it leads to the enhancement of autoradiolytic degradation of [¹⁸F]FDG. However, an increase in the storage temperature of the solutions from 25 to 40°C does not affect the rate of radiation-induced dehalogenation of [¹⁸F]FDG.

The radiolysis of 1-propanol without heating and in a boiling state under the action of accelerated (8-MeV electrons) was investigated. At room temperature, aldehydes dominated among molecular products. Unlike γ-radiolysis, monohydric alcohols were the second most important fraction. The yields of formation of aldehydes, monohydric alcohols, and diols in boiling 1-propanol were approximately equal. Boiling increased the weight fraction of products heavier than 1-propanol to 74%, whereas this fraction was 57% at room temperature. As follows from the analysis of products, boiling accelerated the dissociation of radicals and radical cations and facilitated radical exchange and combinations processes. The yields of 1-propanol degradation were 10.1 ± 0.9 and 13.3 ± 0.9 molecule/100 eV at room temperature and in a boiling state, respectively.

The nature of micropore size distribution in a number of amorphous polymer glasses (membrane materials and sorbents) has been discussed on the basis of data on positron annihilation lifetime spectroscopy (PALS) and low-temperature CO₂ gas sorption (LTGS). The LTGS (CO₂) technique in combination with mathematical processing by the density functional theory gives a multimodal size distribution of micropores in the range of effective diameters of 0.5–1.5 nm for PIM-1 type polymers of intrinsic microporosity. The positron annihilation data (time distribution of annihilation emission events) are also satisfactorily processed under the assumption of multimodality. The results have been discussed in terms of the “local rigidity” of the materials under consideration.

The photoluminescence (PL) method has been used to study the change in the PL spectra of poly(diphenylene phthalide) (PDP) films under the influence of such factors as the wavelength of the exciting light, the duration of exposure to UV light, and annealing. The contribution to the change in the PL spectra of pretreatment of the samples and the structure of the terminal units of the polymer chain has been estimated. The recombination mechanism of experimentally observed processes in PDP films upon UV irradiation and annealing is discussed. These processes include, in particular, the processes of transformation of the lateral and defective fragments of polymer chains, and the reasons for the appearance of the long-wavelength emission band and the change in the ratio of the intensities of the emission bands with maximums at 344 and ~500 nm.

Changes in the composition of the surface layer of Lexan 8010 polycarbonate after treatment in plasma of the positive column of oxygen glow discharge have been investigated. The effect of the amount of the processed polymer on the etching kinetics and surface modification of polycarbonate has been shown. It has been established that an increase in the amount of the polymer processed in plasma leads to a change in the gas phase composition, the concentrations of active species, and their fluxes onto the sample, and, as a consequence, a change in the composition of the modified surface layer of polycarbonate.

A mechanism for the degradation of n-heptane and the formation of the products of its plasma-chemical transformation by microwave discharge treatment has been proposed. Chemical reactions resulting in reactive species, namely free radicals that form lower hydrocarbons and polyaromatic structures are presented. The product composition of the gas, liquid, and solid phases has been studied using gas chromatography–mass spectrometry analysis of the precipitate obtained by evaporation of the liquid phase after the treatment of n-heptane.