I. E. Nifant’ev

Electron-donating ability of triarylphosphines and related compounds studied by 31P NMR spectroscopy

The influence of aryl, heterocyclic, amide, alkyl, alkoxyl, thioalkoxyl, and ferrocenyl substituents at the phosphorus atom on its electron-donating ability was studied by the measurement of direct 31P—77Se spin-spin coupling constants for the corresponding selenides. Series of diphenylorganylphosphines and their selenides were studied.

Controlled Synthesis of Polyacrylonitrile via Reversible Addition-Fragmentation Chain-Transfer Pseudoliving Radical Polymerization and Its Thermal Behavior

The polymerization of acrylonitrile mediated by various trithiocarbonates as reversible addition-fragmentation chain-transfer agents is studied. It is shown that, when polymerization is performed in DMSO, a narrowly dispersed PAN with a controlled molecular mass can be prepared. The pseudoliving radical polymerization of acrylonitrile is conducted for the first time via the reversible addition-fragmentation chaintransfer mechanism in carbon dioxide at an increased pressure. The structure of the polymers is investigated via NMR and IR spectroscopy. As shown by DSC and IR pyrolysis, the thermal behavior of PAN is determined by its molecular mass, the width of the molecular-mass distribution, and the conditions of synthesis. The incorporation of functional groups of the reversible addition-fragmentation chain-transfer agent into a macromolecule changes the structure of the polyconjugated system and makes it possible to control the conditions of its formation.

Effect of Electron Donors on Polymerization of Propylene in the Presence of Titanium—Magnesium Catalysts

The effect of internal and external electron donors on the polymerization of propylene in a liquid monomer or a hydrocarbon diluent (hexane) in the presence of a titanium-magnesium nanocatalyst activated with an organoaluminum compound (triethylaluminum, triisobutylaluminum) and the properties of the resulting PP are studied. The polymerization of propylene in the absence of internal and external donors yields atactic PP, whereas, in the presence of a catalyst containing an aryl internal donor, isotactic PP is formed. The activity and stereospecificity of the catalytic system substantially depends on the method of electron-donor introduction. The thermal treatment of the catalyst with an electron donor affects its activity and stereospecificity.

A study of the polymerization of ethylene on Ti(III) monocyclopentadienyl compounds by the density functional theory method

Density functional theory was used to study model ethylene reactions with CpTiIIIEt+A− (A− = CH3B(C6F5)3−, or B(C6F5)4−; A− can be absent) compounds. The polymerization of ethylene on an isolated CpTiEt+ cation is hindered because of equilibrium between the CpTi(C2H4)Et+ primary complex and the primary product of CpTiBu+ insertion. At the same time, the polymerization of ethylene on CpTiEt+A− ion pairs (A− = CH3B(C6F5)3− or B(C6F5)4−) is thermodynamically allowed (ΔE from −26.2 to −25.6 kcal/mol and ΔG298 from −10.9 to −10.4 kcal/mol) and is not related to overcoming substantial energy barriers (ΔE# = 8.2−12.3 kcal/mol and ΔG298≠) = 7.8−13.3 kcal/mol). The degree of polymerization can be low because of the effective occurrence of polymer chain termination by hydrogen transfer from the polymer chain to the monomer.

Modified titanium-magnesium nanocatalysts in the polymerization of isoprene

The polymerization of isoprene on titanium-magnesium nanocatalysts modified with electron-donor compounds based on organic phosphines and sulfides has been studied. It was shown that the catalyst modification makes it possible to increase the content of trans-1,4 units in polyisoprene up to 97% (according to the data of 1H NMR spectra). In the case of a catalyst modified with tributylphosphine, the effects of the phosphorus-to-titanium ratio on the polymerization kinetics, on the microstructure of trans-1,4-polyisoprene, and on the molecular mass of the polymer have been estimated.

New cysteine-modifying reagents: Efficiency of derivatization and influence on the signals of the protonated molecules of disulfide-containing peptides in matrix-assisted laser desorption/ionization mass spectrometry

Mass spectrometric de novo sequencing of skin secretion peptides from genus Rana is complicated because of C-terminal disulfide cycles present in their structure. Brevinin-1E and brevinin-2Ec from the skin secretion of the Marsh Frog R. ridibunda were used for a comparative study of six N-phenylmaleimide derivatives as new alkylating agents for cysteine thiol moieties. The paper describes the synthesis and confirmation of the structures of the obtained compounds. A procedure was developed for modifying thiol groups with the proposed reagents. Alkylation efficiency and the effect on the peak intensity in matrix-assisted laser desorption/ionization (MALDI) spectra were investigated. The best results were obtained for 2,4- and 2,5-dimethylphenylmaleimides. Additionally tested iodoacetic acid was shown to be a powerful modifier of thiol groups, while its excess notably increases the intensities of the peaks of protonated molecules in the MALDI mass spectra of both peptides.

Polymerization of trimethylene carbonate and lactones in the presence of magnesium monoionolate: A comparative theoretical and experimental study

Using quantum-chemical calculations (DFT, program Priroda), the formation of a catalyst species on the basis of magnesium complexes with 2,6-di-tert-butyl-4-methylphenol is discussed. A comparative theoretical and experimental study of the ring-opening polymerization of trimethylene carbonate, 1,4-dioxanone, δ-valerolactone, and e-caprolactone in the presence of the monoionolate magnesium complex is performed. It is shown that the calculated values of activation barriers correlate with the observed order of activity of cyclic esters. The maximum rate of polymerization is exhibited by trimethylene carbonate.

Titanium–magnesium nanocatalysts of polymerization (Review)

This review addresses the history of the development, structure, properties, and application prospects for a new class of ultrafine catalysts of coordination polymerization, viz., titanium–magnesium nanocatalysts.

A study of the morphology of acrylonitrile-methylacrylateitaconic acid/itaconic acid derivative copolymers synthesized in a supercritical carbon dioxide medium

Ternary copolymers of acrylonitrile with methylacrylate, itaconic acid (IA), and its derivatives, namely, monomethyl ester (MME), monoethyl ester (MEE), monoamide, and mono-n-octylamide, were synthesized in a supercritical carbon dioxide medium. The morphology of the synthesized copolymers was studied by scanning electron microscopy. Copolymers with IA, MME, and MEE were obtained in the form of regularly shaped particles of nearly 1 μm in size without the addition of stabilizers.

New “old” polylactides for tissue engineering constructions

New methods for the synthesis of aliphatic polyesters were proposed and realized with highly effective and low-toxic 1,5,7-triazabicyclo[4.4.0]decene-5 and (2,6-di-tert-butyl-4-methylphenoxy)-butyl-magnesium as catalysts and ethanol as an initiator. The interaction processes between D,L-polylactides of different molecular weights, obtained through these methods, and supercritical carbon dioxide were studied to provide “soft and dry” formation (without high temperatures and toxic organic solvents) of highly porous (up to 90 vol %) bioresorbable matrices for tissue engineering constructions. The chemical structure, molecular weight characteristics, morphology, cytotoxicity, and matrix properties of the samples synthesized from D,L-polylactides were studied with nuclear magnetic resonance spectroscopy, gel permeation chromatography, scanning electron microscopy, colorimetric testing to estimate the metabolic activity of cells (MTT test), and coloration with a vital fluorescent dye of in vitro cultures of multipotent stromal cells of human adipose tissue. A comparative analysis for biocompatibility of these matrices with control samples made from “medical grade” polylactide analog produced industrially indicates that the materials developed can be recommended for tissue engineering.