Volume 53, Nº 5 (2019)

The chain growth in radical chain polymerization is associated with the wave of transformation of primary radicals into macroradicals. The change in chain length n and molecular mass distribution R(t, n) with time t corresponds to the movement of a wave packet with velocity dn/dt and width ∆(n), both dependent on monomer concentration M(t). The formation of macroradicals in the absence of chain transfer when the rate constant of chain growth K(n) depends on n has been considered, and it has been shown that the packet is described by the Poisson distribution law with the event probability depending on K(n) and t. As K(n) decreases, R(t,n) narrows and its maximum shifts to the region of the minimum of K(n). Relations of K(n), M(t), and R(t, n) to dn/dt and ∆(n) have been found.

The effect of cucrbit[7]uril (CB7) on the redox reactions of thionine (ThH⁺) in the triplet state are considered in the absence and the presence of electron donor (FeSO₄) and acceptor (p-nitroacetophenone). The formation of the 1 : 1 host–guest complex between thionine and CB7 increases the lifetime of the thionine triplet state. In the absence of exogenous electron donor and acceptor, the thionine triplet molecules in the host-guest complex enter into reactions of disproportionation and concentration quenching to give semioxidized and semireduced forms of thionine. The yield and lifetime of semioxidized and semireduced thionine forms exceed the yield and lifetime of these forms for free thionine. The complexation of thionine with CB7 decreases the efficiency of the thionine photoreduction and that of the reduction of the semioxidized form by the Fe²⁺ ions by factors of 5 and 2.5, respectively.

Using EPR spectroscopy, it has been established that monomers affect the decomposition rate of their polymerization initiators by forming complexes with them. Several structures of the complexes have been optimized, and their decomposition mechanisms, the activation energies of the chain initiation and propagation reactions, and the heat of polymerization have been determined by means of quantum chemistry methods. In the absence of radical inhibitors (evacuation), the polymerization proceeds with high efficiency (98%) at room temperature without stimulation of the system with external energy.

The dissipative processes of α-, β-, and μ-relaxation in irradiated acrylic latex polymers have been studied by means of dynamic mechanical relaxation spectroscopy. Radiation-induced changes in the temperature position of maxima and intensity of dissipative processes in the internal friction spectra of the polymers have been revealed. The manifestation of the effects depends on the rubber elasticity of the polymer and the presence of functional groups.

Electrophysical parameters of atmospheric pressure discharge with an aqueous potassium permanganate solution as a cathode have been determined. The cathode potential drop, the electric field strength in the positive column of the discharge, and the current density depending on the solution concentration and the discharge current have been found, as well as the emission coefficient γ .

The kinetic features of the oxidation–reduction processes of chromium ions during the treatment of potassium dichromate aqueous solutions with concentrations of 0.092–0.39 mmol/L in atmospheric-pressure dc discharge in oxygen at currents of 20–60 mA have been investigated. The solution served as the cathode of the discharge. It has been found that the discharge induces reversible Cr⁶⁺ ↔ Cr³⁺ redox reactions of chromium ions. The limiting degree of reduction of Cr⁶⁺ ions slightly depends on the discharge current and decreases with an increase in the initial concentration of the solution. The apparent rate constants of oxidation and reduction have been found, and the energy efficiency of the process has been evaluated. The obtained data are compared with previously obtained results for electric discharge in air and argon. It has been shown that the discharge in argon is the most effective for carrying out the reduction process.

The process of hydrogen sulfide removal from methane with an admixture of C₆–C₈n-alkanes in dielectric barrier discharge has been studied. It has been shown that the shortage of liquid hydrocarbon in the initial mixture results in the formation of high molecular polysulfide compounds, and an excess, in the formation of thiols and alkyl sulfides.

Polytetrafluoroethylene-based aerogel has been synthesized for the first time. Graphene oxide has been used as a binder. After reduction with hydrazine and annealing at 370°C, the aerogel surface has been found to become superhydrophobic (the contact angle of water is 162°). Superhydrophobic aerogel with a specific gravity of 30 mg/cm³ has been characterized by IR spectroscopy and X-ray photoelectron spectroscopy.

The influence of the conditions of mask-based photopolymerization of thick layers of a composition (with thickness h from 0.5 to 4.0 mm) based on dimethacrylate OCM-2 and o-quinone photoinitiator on the geometry of the resulting polymer sample has been studied. Upon photopolymerization of layers through a slit aperture of width l, the polymer formed has a cross section of trapezoid, the large base of which faces to the side of illumination. With increasing exposure, the difference in the sizes of the bases of the trapezoid decreases, which reduces roughness of an object composed of such layers. For stereolithographic synthesis of a 3D model from layers with h = 0.5 and 1.0 mm and roughness of 10 μm, the minimum slit width is achieved at l ≈ 2h.