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.

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.

RAFT polymerization was applied for the synthesis of hydrophilic poly(N,N-dimethylaminoethyl methacrylate) and random copolymers of N,N-dimethylaminoethyl methacrylate, containing 5 or 10 mol

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.

Controlled synthesis of terpolymers of acrylonitrile with acrylamide and alkyl acrylate of similar composition but differing in the alkyl substituent (methyl, butyl, 2-ethylhexyl, and lauryl) has been performed for the first time via the reversible addition-fragmentation chain transfer polymerization under the action of dibenzyl trithiocarbonate. Investigation of thermal behavior of the terpolymers under inert atmosphere has allowed determination of the activation energy of the ionic cyclization as of ~80 kJ/mol irrespectively of the alkyl acrylate nature. Mechanism of chemical transformations of the terpolymers under isothermal treatment at 250°C has not differed from this known for the binary acrylonitrile–acrylamide and acrylonitrile–alkyl acrylate copolymers. At the same time, the rate of the polyconjugated structure formation has been higher in comparison with the analogous terpolymers with acrylic acid. The rate of the stabilization has changed along the following series of alkyl acrylates: methyl acrylate < butyl acrylate ≈ 2-ethylhexyl acrylate < lauryl acrylate. Concentration ranges of the dilute, semidilute, and concentrated solutions have been determined for the synthesized terpolymers.

Copolymers of acrylonitrile (AN) and 1-vinyl imidazole (VIM) are synthesized through free radical and reversible addition–fragmentation chain transfer (RAFT) polymerization in DMSO. It is demonstrated that reactivity of VIM in copolymerization is lower than that of AN ( r VIM = 0.22 ± 0.02 and r AN = 0.88 ± 0.02). The copolymer composition is held constant throughout copolymerization in the range of monomer feed up to 30 mol % of VIM providing the formation of copolymers with high compositional homogeneity. RAFT mechanism provides additionally the low dispersity of the copolymers. The study of thermal stabilization processes of the synthesized copolymers reveals that molecular weight distribution plays minor role in the thermal behavior of acrylonitrile copolymers with 1-vinyl imidazole in contrast to copolymer composition. The activation energy of cyclization reaction increases linearly with the increase of VIM content in copolymer. The increase of VIM molar part in the copolymer is followed by slower evolution of the ladder structure. Generally, VIM may be considered as an inert monomer. At a constant temperature, the rate of the formation of ladder structure under inert atmosphere and in air differs drastically. The conversion of nitrile groups in –C=N– groups equal to 10% is achieved after 2.5 h of thermal treatment in argon or in 15 min in air. The essential difference in the rates of cyclization reactions in argon and air allow to develop new strategy for production of melt-processable precursors of carbon fiber.

The regularities of the seeded polymerization of styrene in an aqueous-alcoholic medium in the presence of the seed particles of the triblock copolymer of acrylic acid and butyl acrylate, containing the trithiocarbonate group within the chain and acting as a reversible chain transfer agent, were studied for the first time. The influence of the composition of the dispersion medium and of the concentrations of components on the polymerization kinetics, molecular weight characteristics of the reaction products, and size distribution of the resultant particles was evaluated. Immobilization of the TiO2 nanoparticles on the polymeric particles of the block copolymers in the course of the seeded polymerization of styrene was carried out. Stable suspensions of the hybrid particles with an average diameter of 60 to 130 nm, comprising TiO2 and the block copolymer of acrylic acid, butyl acrylate, and styrene, were obtained.

Radical polymerization of acrylonitrile in the presence of N-methylmorpholine N-oxide has been performed for the first time. It has been shown that the presence of N-methylmorpholine N-oxide leads to the decrease in the molecular mass of the polymer and induces its partial cyclization. These features have been preserved when N-methylmorpholine N-oxide has been introduced in the polymerization simultaneously with the monomer and the initiator as well as when it has been added at high conversion of the monomer. The introduction of N-methylmorpholine N-oxide into polyacrylonitrile has led to the cyclization of the nitrile units in two stages, the low-temperature one being initiated by N-methylmorpholine N-oxide and the high-temperature one, typical of pure polyacrylonitrile. The ratio between the intensity of these processes has been governed by the content of N-methylmorpholine N-oxide.

Using asymmetric trithiocarbonate-mediated reversible addition-fragmentation chain transfer polymerization, terpolymers of acrylonitrile with acrylic acid and alkyl acrylate are synthesized; methyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and lauryl acrylate are used as an alkyl acrylate. The molecular structure of the terpolymers is set by varying composition of the monomer mixture and regime of introducing acrylic acid and alkyl acrylate into the reaction medium, instantaneously or continuously in the course of synthesis, and the molecular weight of the terpolymer is specified by the concentration of trithiocarbonate. Study of the thermal behavior of the synthesized terpolymers shows that the temperature interval of cyclization and the intensity of heat release depend on the amount and molar ratio of acrylic acid to alkyl acrylate. At the molar fraction of acrylonitrile ~90%, the nature of alkyl acrylate insignificantly affects the thermal effect of cyclization of nitrile groups; however, the distribution of acrylic acid and acrylonitrile units in the terpolymer influences the ratio between ionic and radical mechanisms of cyclization. Similar effects are observed in the thermal treatment of the terpolymers in air. An analysis of a change in the chemical structure of the terpolymers upon thermal treatment in an inert atmosphere and in air indicates that lengthening of the alkyl substituent in alkyl acrylate contributes to an increase in the length of the system of conjugated bonds and the effect of chain microstructure on it becomes more pronounced on going from methyl acrylate to lauryl acrylate.

Copolymers of acrylonitrile and ethyl 2-cyanoacrylate have been synthesized for the first time. It has been shown that the copolymers with controllable molecular mass and narrow molecular mass distribution are formed under conditions of radical initiation in the presence of 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid as a reversible chain transfer agent. Relative reactivities of the monomers in the copolymerization ( r 1 = 0.052 ± 0.02 for acrylonitrile and r 2 = 54.5 ± 7.2 for ethyl 2-cyanoacrylate) have been determined. Copolymers with different microstructure have been synthesized using different methods to introduce ethyl 2-cyanoacrylate in the copolymerization (simultaneous and continuous charging). It has been shown that two competing processes, depolymerization and cyclization of the nitrile units, occur during heating of the copolymers under inert atmosphere. Probability of depolymerization has been increased with the increase in the fraction of ethyl 2-cyanoacrylate in the copolymer and the change of the gradient copolymer structure to the statistical one.

The laws of dispersion polymerization of n-butyl acrylate in an aqueous-alcoholic medium in the presence of a hydrophilic reversible addition-fragmentation chain-transfer poly(acrylic acid)-based polymeric agent with a trithiocarbonate group within the chain are investigated. It is shown that the portioned introduction of the monomer into the synthesis makes it possible to achieve higher maximum conversions. The resulting block copolymers are characterized by a relatively narrow molecular weight distribution and their number-average molecular weight increases linearly with increasing monomer concentration. The obtained dispersions of triblock copolymer poly(acrylic acid)–block-poly(n-butyl acrylate)–block-poly(acrylic acid) have a unimodal particle size distribution that persists after dialysis against water. It is shown that the synthesized dispersions may be used as a polymer matrix for immobilizing zinc oxide nanoparticles and as a polymer precursor in the process of the seeded polymerization of styrene.

The possible reasons for the occurrence of emulsion polymerization of a monomer simultaneously with suspension polymerization, namely the formation of polymer particles from a highly dispersed fraction of monomer droplets in the initial emulsion and associates of high molecular weight surfactants, are considered. Data on colloidal solubility of monomer in surfactant associates and data on determination of hydrodynamic radii of high molecular weight surfactant associates are presented. The results obtained can be the basis for the choice of surfactants in suspension polymerization, which ensure the minimum contribution of the highly dispersed fraction of monomer droplets to the formation of polymer-monomer particles.

The possible reasons for the occurrence of emulsion polymerization of a monomer simultaneously with suspension polymerization, namely the formation of polymer particles from a highly dispersed fraction of monomer droplets in the initial emulsion and associates of high molecular weight surfactants, are considered. Data on colloidal solubility of monomer in surfactant associates and data on determination of hydrodynamic radii of high molecular weight surfactant associates are presented. The results obtained can be the basis for the choice of surfactants in suspension polymerization, which ensure the minimum contribution of the highly dispersed fraction of monomer droplets to the formation of polymer-monomer particles.

A comparative study of the thermal behavior of acrylonitrile-acrylic acid copolymers synthesized by conventional radical polymerization and reversible addition-fragmentation chain transfer polymerization to deep conversions with different modes of introducing acrylic acid into the reaction is carried out. It is shown that, at similar average compositions of conventional copolymers, the difference in their compositional heterogeneity leads to an unpredictable change in the activation energy of cyclization, the degree of stabilization, and the thermal stability of the copolymers. In contrast, for copolymers of the same average composition obtained under reversible chain transfer conditions, a change in the chain microstructure, that is, the distribution of acrylic acid units along the chain, makes it possible to control the rate of cyclization while maintaining a high thermal stability of the copolymers.

The latest achievements in the field of synthesis of acrylonitrile copolymers are summarized. New ecofriendly methods of synthesizing acrylonitrile copolymers in ionic liquids and supercritical media are analyzed. The potential of various techniques of controlled radical and anionic polymerizations in tailoring the structure and properties of acrylonitrile copolymers is discussed. Methods for the synthesis of acrylonitrile copolymers, which may be used for the melt spinning of fibers, are considered. A patent search is conducted, and information relevant to new methods and recipes for the synthesis of acrylonitrile copolymers is generalized.

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.