Vol 92, No 6 (2019)

Specific features of homogeneous, heterogeneous, and nanoheterogeneous catalysis in hydrogenation of polymers and the advantages and drawbacks of various catalytic systems are considered. Differences in hydrogenation of polymers and monomers are discussed. Specific features of the behavior of polymer molecules, complicating the heterogeneous catalysis, are noted, such as diffusion of macromolecules into catalyst pores, conformational limitations, and rheology of polymer solutions. The main catalytic systems studied in polymer hydrogenation are listed. A separate section deals with hydrogenless hydrogenation of polymers. The properties and application fields of hydrogenated polymers are analyzed. Promising directions of studying the catalysis of hydrogenation of macromolecular compounds are outlined.

Process of thermolysis of sodium borohydride dihydrate samples produced from solution and via a vapor was considered. A study of an acetonitrile solution made by the method of nuclear magnetic resonance demonstrated that the stoichiometry is observed in both cases. An X-ray diffraction analysis evidenced that the sample produced via a vapor is defective. It was found that, in both cases, the process begins after the reaction of peritectic decomposition of the starting compound occurs and a liquid phase is formed. The enthalpy of the peritectic reaction was determined to be ΔH_react = 18.6 ± 1.5 kJ mol⁻¹ for the sample crystallized from an alkaline solution. For the sample produced via a vapor, this quantity is substantially smaller. The kinetics of a low-temperature thermolysis (40–80°C) of both samples is described by the Avrami—Erofeev equation.

Results obtained in a study of the process of synthesis of a polydisperse boron carbide powder (average particle size 2.10 µm) characterized by a broad particle size distribution are presented. The process in which a ceramic is produced from the thus synthesized boron carbide by hot compaction was also analyzed. In some cases, a sintering additive, highly dispersed chromium carbide powder (average particle size 7.13 µm), was used. The hot compaction was performed in argon at moderate parameters: pressure 35 MPa and temperature 1950°C. The porosity and water-absorption capacity of the samples obtained are very low and do not exceed 0.02%. The average values of the bending and compression strengths were 406 and 1553 MPa, respectively. A microhardness of about 42 GPa was reached in sintering of boron carbide. The microhardness in sintering of boron carbide with addition of chromium carbide was 45–46 GPa.

The modification of natural rubber with poly(diallyldimethylammonium chloride) and polyvinyl chloride by mixing latexes was studied. It was established that coagulation with polyelectrolyte contributes to preservation of non-rubber components and reduction of the Mooney rubber viscosity, and the introduction of polyvinyl chloride increases the oil and gasoline resistance of the compositions. The revealed effects are explained by the influence of the natural rubber microstructure and polyvinyl chloride on the macroscopic properties of their blends.

Conditions were found for controlled reversible addition-fragmentation chain-transfer radical polymerization to obtain narrow-dispersity gradient methacrylic acid-methyl acrylate copolymer (M_n = 1.59 × 10⁴). A copolymer of similar composition and molecular mass (M_n = 1.81 × 10⁴) with random distribution of units was obtained by radical copolymerization in the presence of dodecyl mercaptan. The behavior of the gradient and random copolymers, each containing ∼14 mol % methacrylic acid units, was studied in solutions, Langmuir monolayers, and Langmuir-Blodgett films. Several ranges of the existence of associates and micelles, preserved upon transfer in a Langmuir-Blodgett film, were revealed for the narrow-dispersity copolymer at the water-air interface depending on pH of the subphase. Associates in the form of ribbon structures and molecular ensembles of nanometric size (network structure with loop-like fragments) are observed in the AFM images of Langmuir-Blodgett films of the gradient and random copolymers, respectively.

The influence of supported titanium-magnesium catalysts with various internal and external donors on the propylene polymerization in the liquid monomer medium and the characteristics of the polypropylene formed were studied. The following internal donors were used: dibutyl phthalate, diisobutyl phthalate, 9,9′-bis(methoxymethyl) fluorene, and diethyl 2,3-diisopropylsuccinate. The catalysts studied allow synthesis of polypropylene with high isotacticity (>96%) and different molecular-mass distribution (M_w/M_n from 3.3 to 6.3). The influence of external donors (alicyclic, amine) in combination with phthalate and nonphthalate electron-donor compounds on the stereospecificity and activity of the catalysts and on their sensitivity to hydrogen was studied. The optimum catalytic systems for preparing polypropylene for various purposes can be found by varying pairs of internal and external donors.

The aminophosphine ligand was synthesized by the reaction of N-ethylaniline with chlorodiphenylphosphine in the presence of triethylamine at low temperature. Oxidation of the ligand with elemental sulfur or selenium afforded the corresponding aminophosphine sulfide and selenide. The compounds were characterized by elemental analyses, IR, ¹H and ³¹P NMR. N-diphenylphosphino-N-ethylaniline and its chalcogen derivatives were used as ligands in solvent extraction of metal picrates such as Cd²⁺ and Ni²⁺ from the aqueous to the organic phase. Influences of parameters such as pH of the aqueous phase, solvent, extraction time, and extradant concentration were investigated to determine the extraction ability of ligands for metal ions. Results of the experiments showed that an extractability of 95.5 and 97.8%, respectively for Ni²⁺, and Cd²⁺ at pH 2 could be achieved.

Possibility was found of using the sodium borohydride additive in technologies for electrodeposition of nickel-boron coatings with various compositions and functional properties. The composition of a complex alkaline tartrate nickel-plating electrolyte at which this additive can be used is recommended. The main parameters of the electrodeposition process and some properties of coatings obtained in the given electrolyte were examined. It was shown that sodium borohydride affects the throwing power of the electrolyte, current efficiency by nickel in its electrodeposition, composition of the nickel-boron alloy, and its internal stresses and microstructure.

Method of potentiodynamic polarization was used to study the electrodeposition of a copper-tin alloy from an oxalic acid electrolyte with addition of 10⁻⁵–10⁻³ mol dm⁻³ of trimethyloctylammonium chloride, N-octylpyridinium bromide, and N-benzylpyridinium bromide. Introduction of these compounds changes the rate of the cathodic reduction of tin. It was found that the nature and concentration of the additives introduced into the electrolyte affects the composition, structure, glossiness, and roughness of the Cu-Sn coatings being formed. It was shown that introduction into an electrolyte of trimethylammonium chloride and N-octylpyridinium bromide inhibits the deposition of tin and favors formation of lustrous and semilustrous coatings containing 24.4–35.8 wt % tin. The presence of N-benzylpyridinium bromide in an oxalic acid electrolyte intensifies the cathodic reduction of tin and leads to formation of matte coatings containing up to 42.5 wt % tin.

In this paper, citric acid was used as carbon source, diethylenetriamine and urotropine were used as precursors, and N-doped carbon dots (cdh-CDs) with luminescent properties were synthesized by microwave method. The structure of the sample was analyzed by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray diffractometry (XRD), ultraviolet spectrophotometer (UV), fluorescence spectroscopy, etc., and it was proved that cdh-CDs with an amorphous structure about 4–10 nm in diameter was synthesized. The corrosion inhibition performance of cdh-CDs in 1 M hydrochloric acid was evaluated by static weight loss and electrochemical method. The results showed that cdh-CDs have a good corrosion inhibition performance at 60°C, the inhibition efficiency can reach 81.2% when the dosage is 600 ppm. Electrochemical results showed that cdh-CDs are mixed inhibitors which mainly inhibit cathodes.

Aldol condensation of furfural with acetone and a series of aldehydes in the presence of PAF-SO₃H acid catalyst based on mesoporous aromatic frameworks was studied. The reaction course depending on the process temperature, catalyst amount, and reactant ratio was studied for the furfural condensation with acetone as an example. The catalyst can be reused in several cycles without appreciable activity loss.

Results of laboratory studies of the extraction of light mercaptans (methyl, ethyl, and propyl mercaptans) from hydrocarbons mixtures with a 25% aqueous solution of ammonia (caustic ammonia) are presented and discussed. It is shown that aqueous ammonia can in principle be used for controlled demercaptanization of light hydrocarbon fractions and liquefied hydrocarbon gases containing hydrogen sulfide and lower mercaptans. The advantage of this demercaptanization method over the conventional processes of alkali treatment is that there is no stage of oxidative catalytic regeneration of a spent alkali and there are no its highly toxic wastes, sulfurousalkaline waste waters. The regeneration of a spent (saturated with sulfurous compounds) aqueous ammonia can be comparatively easily performed by its heating (boiling), which leads to a hydrolytic decomposition of ammonium sulfides and mercaptides to release their constituent gases: hydrogen sulfide, mercaptans, and ammonia. Ammonia is recycled into the process as freshly prepared (regenerated) caustic ammonia.