Nickolay I. Prokopov

Binary and ternary copolymers of acrylonitrile (AN), tert-butyl acrylate (TBA), and n-butyl acrylate (BA) are synthesized through conventional radical polymerization in DMSO in the presence of 2-mercaptoethanol. The thermal behavior of binary and ternary copolymers is studied under argon atmosphere and in air. It is demonstrated that the copolymers of AN contain 1–10 mol.% of TBA split isobutylene upon heating above 160 °C, resulting in the formation of the units of acrylic acid in the chain. The carboxylic groups formed in situ are responsible for the ionic mechanism of cyclization, which starts at lower temperatures compared with pure polyacrylonitrile (PAN) or AN copolymer with BA. The activation energy of cyclization through ionic and radical mechanisms depends on copolymer composition. For the ionic mechanism, the activation energy lies in the range ca. 100–130 kJ/mole, while for the radical mechanism, it lies in the range ca. 150–190 kJ/mole. The increase in the TBA molar part in the copolymer is followed by faster consumption of nitrile groups and the evolution of a ladder structure in both binary and ternary copolymers. Thus, the incorporation of a certain amount of TBA in PAN or its copolymer with BA allows tuning the temperature range of cyclization. This feature seems attractive for applications in the production of melt-spun PAN by choosing the appropriate copolymer composition and heating mode.

Polymerization-induced self-assembly (PISA) is a powerful and versatile technique for producing colloidal dispersions of block copolymer particles with desired morphologies. Currently, PISA can be carried out in various media, over a wide range of temperatures, and using different mechanisms. This method enables the production of biodegradable objects and particles with various functionalities and stimuli sensitivity. Consequently, PISA offers a broad spectrum of potential commercial applications. The aim of this review is to provide an overview of the current state of rational synthesis of block copolymer particles with diverse morphologies using various PISA techniques and mechanisms. The discussion begins with an examination of the main thermodynamic, kinetic, and structural aspects of block copolymer micellization, followed by an exploration of the key principles of PISA in the formation of gradient and block copolymers. The review also delves into the main mechanisms of PISA implementation and the principles governing particle morphology. Finally, the potential future developments in PISA are considered.

This article presents the results of investigations on heterophase polymerization of vinyl monomers in the presence of organosilicon compounds of different structures. On the basis of the detailed study of the kinetic and topochemical regularities of the heterophase polymerization of vinyl monomers, the conditions for the synthesis of polymer suspensions with a narrow particle-size distribution using a one-step method have been determined.

In this research, we have developed the approach to controlled synthesis of acrylonitrile-acrylamide copolymers with narrow molecular weight distribution and various monomer sequence distributions. By using dibenzyl trithiocarbonate and batch/semibatch polymerization, we have first synthesized random, gradient, and block-gradient copolymers containing 3.4–10.2 mol. % of acrylamide and revealed the influence of the monomer sequence on the cyclization behavior of poly(acrylonitrile-co-acrylamide) by combination of differential scanning calorimetry and Fourier transform infrared spectroscopy. This allowed us to find differences in cyclization behavior of the copolymers in argon and air atmosphere. Intramolecular cyclization was the main process proceeding in argon atmosphere. The radical mechanism of cyclization was suppressed already at the molar part of acrylamide units in copolymer exceeding ~3 mol. % for random copolymer and ~6 mol. % for block-gradient copolymer. The activation energy of ionic cyclization was equal to 89 ± 3 kJ·mol⁻¹ and was not influenced by both copolymer composition and chain microstructure in contrast to the rate of cyclization. The latter was increased with the rise of acrylamide content, the content of hetero-triads and in the range block-gradient < gradient < random structure. In air atmosphere, the oxidation reactions dominated over cyclization. The oxidation reactions were found to be less sensitive to copolymer composition and chain microstructure.

The review summarizes recent advances in the production of carbon fiber precursors based on melt-spun acrylonitrile copolymers. Approaches to decrease the melting point of polyacrylonitrile and acrylonitrile copolymers are analyzed, including copolymerization with inert comonomers, plasticization by various solvents and additives, among them the eco-friendly ways to use the carbon dioxide and ionic liquids. The methods for preliminary modification of precursors that provides the thermal oxidative stabilization of the fibers without their melting and the reduction in the stabilization duration without the loss of the mechanical characteristics of the fibers are discussed. Special attention is paid to different ways of crosslinking by irradiation with different sources. Examples of the carbon fibers preparation from melt-processable acrylonitrile copolymers are considered in detail. A patent search was carried out and the information on the methods for producing carbon fibers from precursors based on melt-spun acrylonitrile copolymers are summarized.

Introduction. The actual internal and external context of the university, in particular the COVID-19 pandemic, creates generates risks for the quality of education at the university. Risk management should be carried out systematically to reduce the probability of occurrence and negative consequences of risks. The purpose of the research is to develop and implement a risk management model involving systemic actions with risks for education at the university and to study the impact of the COVID-19 pandemic on these risks. Methods. Identification of possible risks for quality of education was carried out for the Russian Technological University (Russia). The risk analysis was carried out by written survey with fixing the potential causes and consequences of the risk. The survey involved teachers of all institutes (8) and departments of the university (about 100). The number of participants was more than 2000 people including heads of institutes and departments. The risk method is the analysis of the types, consequences and criticality of failures – FMECA. Research results. The risk management model of the educational process allows organizing the management of internal and external risks for university is presented. The data obtained showed that "poor school preparation in mathematics for mastering the programs of the technological university" was recognized as an unacceptable risk (RPN=74.8). The risk of "full transition to distance learning technologies" was recognized as critical for the quality of the educational process of the university (RPN=40.8). The source of this risk is the existing epidemiological situation in the country and the world caused by the COVID-19 pandemic. Control actions to reduce this risk have been developed within the university: reducing the probability of a risk event and reducing the consequences. The remaining risks were moderate or insignificant, a decision was made to accept them, continue monitoring and analysis in subsequent periods. Conclusions. Proposed risk management model allows the university to identify risks that could potentially have a negative impact on the educational process, to analyze and evaluate them. Priority risks are eliminated or minimized ensures the university's resilience to the impact of internal and external factors for quality of education.

The influence of introducing acrylic acid (AA) into the reaction mixture with acrylonitrile at the synthesis of copolymers by free-radical polymerization (FRP) and radical polymerization with reversible addition–fragmentation chain transfer (RAFT) on the rheological properties of their solutions in dimethyl sulfoxide, as well as on the capability to spin fibers by the mechanotropic method, is analyzed. The influence of AA dosing conditions on the rheological properties of the solutions in the concentration range above the crossover point was not revealed. In the case of RAFT synthesis, the rheological properties differ distinctively in the high concentration region that is expressed by unusual viscoelastic characteristics. Dilute solution viscometry revealed the influence of the comonomer loading order on the interaction intensity of the copolymer macromolecules with a solvent, which is more pronounced for samples synthesized by FRP and can be associated with the copolymers’ molecular structure. Fiber spinning from solutions of polyacrylonitrile and its copolymers (PAN) synthesized by the RAFT method was not able to achieve a high degree of orientation drawing, while for polymers with a wider molecular weight distribution synthesized by FRP, it was possible to realize large stretches, which led to high-quality fibers with strength values up to 640 MPa and elongation at a break of 20%.

The copolymers of acrylonitrile and acrylic acid are synthesized for the first time by trithiocarbonate-mediated reversible addition-fragmentation chain transfer polymerization in DMSO at a content of comonomers in the reaction mixture of 40%. Various regimes of acrylic acid introduction into the reaction are tested. This makes it possible to synthesize copolymers with close average composition and different unit distribution in a chain. It is shown that, with an increase in the fraction of acrylic acid in the copolymer, the contribution of the ionic mechanism of cyclization grows, which is favorable for widening the temperature interval of cyclization and decrease in the intensity of heat flow. Reduction in the rate of introduction of acrylic acid into copolymerization and, as a consequence, its more uniform distribution in the chain lead to analogous effects and cause a decrease in the activation energy of cyclization by both the ionic and radical mechanism. Thus, the use of reversible addition-fragmentation chain transfer polymerization with the dosed introduction of the comonomer allows one to tune the properties of the copolymers during their heat treatment.

Amphiphilic narrow dispersed copolymers of acrylic acid and fluoroalkyl acrylates are synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization using dibenzyl trithiocarbonate in DMF solution. These copolymers and polyacrylic acid containing the trithiocarbonate group within the polymeric chain are used for the synthesis of triblock copolymers in organic, aqueous–organic or aqueous media by chain extension with n-butyl acrylate or its mixture with fluoroalkyl acrylates. Both dispersion polymerization and emulsifier-free emulsion polymerization lead to self-assembling of triblock copolymers in the core–shell particles; the former route provides the formation of microstructured polymer films with a percolated structure.

It is shown that the nature of an initiator affects the molecular mass and molecular-mass distribution of a polymer and, thus, substantially contributes to the strength and rheological characteristics of the interfacial adsorption layer formed on the surface of polymer-monomer particles and the stability of these particles during polymerization.