Controlled radical polymerization of styrene mediated by dithiobenzoates as reversible addition-fragmentation chain-transfer agents

The radical polymerization of styrene at 60 and 80°C mediated by benzyl dithiobenzoate and poly(styrene dithiobenzoate) as reversible addition-fragmentation chain-transfer agents has been studied. It has been shown that both agents are characterized by high chain-transfer constants and provide control over molecular-mass characteristics of polymerization products. The number-average molecular mass of polystyrene linearly grows with conversion, and the polymers are characterized by low values of polydispersity indexes. It has been demonstrated that the rate of polymerization significantly decreases with an increase in the concentration of reversible addition-fragmentation chain-transfer agents. This effect is typical of styrene polymerization mediated by dithiobenzoates. The possible reasons for this phenomenon are discussed.     

Controlled radical polymerization of styrene and <Emphasis Type="Italic">n</Emphasis>-butyl acrylate mediated by trithiocarbonates

The free-radical bulk homopolymerization of styrene and n-butyl acrylate at 80°C mediated by dibenzyl trithiocarbonate, poly(styryl) trithiocarbonate, or poly(n-butyl acrylate) trithiocarbonate as reversible addition-fragmentation chain-transfer agents has been studied. It has been shown that the use of low-and high-molecular-mass reversible addition-fragmentation chain-transfer agents makes it possible to efficiently control the molecular-mass characteristics of polymers. In the case of styrene, the rate of polymerization slightly depends on the concentration of the addition-fragmentation chain-transfer agent. In contrast, for the polymerization of n-butyl acrylate, the rate significantly decreases with the concentration of the chain-transfer agent. Formation of radical intermediates during the polymerization of styrene and n-butyl acrylate mediated by trithiocarbonates has been studied by ESR spectroscopy. It has been demonstrated that the polymeric chain-transfer agents are efficient for the synthesis of block copolymers with the controlled block length.     

Pseudoliving polymerization of vinyl acetate mediated by reversible addition-fragmentation chain-transfer agents

The homopolymerization of vinyl acetate mediated by dithiobenzoates and trithiocarbonates as reversible addition-fragmentation chain-transfer agents is studied. The polymerization of vinyl acetate is characterized by some distinct features: (i) a substantial role of chain-termination reactions involving radical intermediates in the kinetics of the process that increases as the concentrations of the reversible additionfragmentation chain-transfer agent and the initiator increase and as temperature decreases and (ii) the occurrence of side reactions of chain transfer to monomers and polymers. The role of these reactions significantly increases with conversion of the monomer. Thus, in order to prepare a narrowly dispersed PVA via the reversible addition-fragmentation chain-transfer mechanism, the process should be conducted to small conversions (15–20%) at moderately high temperatures (80°C) and at a small molar excess of the reversible addition-fragmentation chain-transfer agent with respect to the initiator. A technique for the synthesis of block copolymers based on PVA and poly(n-butyl acrylate) via the reversible addition-fragmentation chain-transfer mechanism is developed.     

Pseudoliving radical polymerization of methyl methacrylate in the presence of S,S′-bis(methyl-2-isobutyrate) trithiocarbonate

The polymerization of MMA mediated by symmetric trithiocarbonate as a reversible addition-fragmentation chain-transfer agent is studied. It is shown that the process proceeds according to the two-stage pseudoliving radical mechanism. The polymeric reversible addition-fragmentation chain-transfer agent is more efficient than its low-molecular-mass analog. The use of the polymeric reversible addition-fragmentation chain-transfer agent makes it possible to synthesize narrowly dispersed homopolymers of MMA and related copolymers with a controllable molecular mass. Both chain-transfer agents have practically no effect on the initial rate of copolymerization but allow weakening or even suppression of the gel effect at high conversions.     

Controlled synthesis of oligomeric poly(acrylic acid) and its behavior in aqueous solutions

The controlled synthesis of oligomeric poly(acrylic acid) via the pseudoliving radical reversible addition-fragmentation chain-transfer polymerization of acrylic acid in bulk is developed. It is shown that, at high concentrations of reversible addition-fragmentation chain-transfer agents, the polymerization of acrylic acid in bulk occurs via the pseudoliving mechanism, as evidenced by a linear increase in the numberaverage molecular mass of oligomers with conversion and a narrow molecular-mass distribution of the reaction products. The surfactant properties and behavior of the oligomers in aqueous solutions are studied.     

Synthesis of photochromic liquid-crystalline triblock copolymers by pseudoliving reversible addition-fragmentation chain-transfer polymerization

Symmetric photosensitive fully liquid-crystalline triblock copolymers are synthesized by pseudo-living reversible addition-fragmentation chain-transfer radical polymerization for the first time. The polymerization of 3-[methyl(phenyl)amino]propyl acrylate mediated by three different symmetric trithiocarbonates with various leaving groups is studied. It is shown that reversible addition-fragmentation chain-transfer agents make it possible to synthesize narrowly dispersed homopolymers with controlled molecular masses. Poly[(3-[methyl(phenyl)amino]propyl acrylate) trithiocarbonates] are used as polymeric reversible addition-fragmentation chain-transfer agents in the block copolymerization of the phenyl benzoate acrylic monomer. The chemical modification of block copolymers yields desirable photosensitive triblock copolymers containing azobenzene groups. The effect of the molecular structure of triblock copolymers on their phase behavior and thermal properties is examined.     

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.     

Controlled free-radical copolymerization of maleic anhydride and divinyl ether in the presence of reversible addition-fragmentation chain-transfer agents

The free-radical alternating cyclocopolymerization of maleic anhydride and divinyl ether is studied at 60–80°C in the presence of benzyl dithiobenzoate and dibenzyl trithiocarbonate as reversible addition-fragmentation chain-transfer agents. It is shown that the structure of the repeating unit of the cyclocopolymer prepared in the presence of a reversible addition-fragmentation chain-transfer agent coincides with the structure of the repeating unit of the copolymer synthesized under the conditions of conventional free-radical cyclocopolymerization. When the cyclocopolymer is used as a reversible addition-fragmentation chaintransfer agent, a successive increase in the molecular mass of the copolymer with conversion and formation of the block copolymer in the polymerization of styrene are unambiguous evidence that the copolymerization proceeds according to the pseudoliving radical mechanism.     

Controlled free-radical azeotropic copolymerization of styrene and n-butyl acrylate in the presence of tert-butyl dithiobenzoate

The free-radical azeotropic bulk copolymerization of styrene and n-butyl acrylate at 90°C mediated by tert-butyl dithiobenzoate and copoly(strene—n-butyl acrylate) dithiobenzoate as reversible chain-transfer agents has been studied. It has been shown that low-and high-molecular mass chain-transfer agents allow one to efficiently control the molecular-mass characteristics of the copolymers. For all studied systems, the molecular mass linearly increases with conversion, and the copolymers are characterized by low polydispersity indexes. When polystyryl dithiobenzoate and poly(butyl acrylate) dithiobenzoate are used as polymer reversible chain-transfer agents in the azeotropic copolymerization of styrene and n-butyl acrylate, the diblock copolymers with the controlled block lengths are prepared. As evidenced by ESR studies, radical intermediates are formed in the course of the azeotropic copolymerization of styrene and n-butyl acrylate mediated by tert-butyl dithiobenzoate and the copolymer reversible chain-transfer agent; the kinetics of formation of these intermediates has been investigated. It has been demonstrated that the rate of the azeotropic copolymerization mediated by low-and high-molecular-mass reversible chain-transfer agents decreases with an increase in their concentration. The possible causes of this phenomenon are discussed.     

Controlled synthesis of acrylic homo- and copolymers in the presence of trithiocarbonates as reversible addition-fragmentation chain transfer agents

Formation of homo- and copolymers of various structures (random and block) based on tert-butyl acrylate and n-butyl acrylate via polymerization mediated by trithiocarbonates as reversible addition-fragmentation chain-transfer agents has been studied. The process is found to proceed according to a three-stage mechanism. As a result, it is possible to synthesize symmetric triblock copolymers with the use of polymer trithiocarbonates; the polymer reversible addition-fragmentation chain transfer agent predetermines the composition and molecular mass of end blocks, the composition of the monomer mixture determines the structure of the central block, and the concentration of the agent and the conversion of the monomers define its molecular-mass characteristics. The modification of polymerization products gives rise to amphiphilic copolymers.     

Controlled Synthesis of Methacrylic Acid-Methyl Acrylate Copolymers and Their Properties at Various Interfaces

Russian Journal of Applied Chemistry - Conditions were found for controlled reversible addition-fragmentation chain-transfer radical polymerization to obtain narrow-dispersity gradient methacrylic...     

Controlled free-radical polymerization of methyl acrylate in the presence of a cyclic trithiocarbonate under γ-ray irradiation at low temperature

Controlled radical polymerization of MA has been achieved in the presence of a cyclic trithiocarbonate, 1,5-dihydro-2,4-benzodiehiepine-3-thione, under γ-ray irradiation (60 Gy/min) at low temperature. The narrow molecular weight distributions and the linear kinetics curve indicate that the polymerization is a controlled free-radical process at low temperature (especially at −76 °C). The structures of resultant polymers were characterized by matrix assisted laser desorption/ionization time-of-flight mass spectrometry, and the results show that cyclic polymers can be formed at −76 °C, which may result from the reduced diffusion rate and the suppressed chain-transfer reaction at the lower temperature. It is further evidenced that the good control of the polymerization at the lower temperature may be associated with the suppressed chain-transfer reaction, not like reversible addition-fragmentation transfer polymerization. The linear polymers probably result from the polymer chain radicals reacting with the radicals produced by the interaction of the irradiation and the monomer.     

Effects of synthesis conditions and the mechanism of homopolymerization of acrylonitrile on the thermal behavior of the resulting polymer

The effect of the conditions of polyacrylonitrile synthesis (nature of the solvent, homogeneity of the reaction medium, and type of initiation) on the conditions of formation of the polyconjugation system during the pyrolysis of polyacrylonitrile is studied. The controlled synthesis of polyacrylonitrile via radiation polymerization mediated by dibenzyl trithiocarbonate as a reversible addition-fragmentation chain-transfer agent at 25 and 80°C is performed for the first time. It is shown that the type of initiation in reversible addition-fragmentation chain-transfer polymerization (material initiation or radiolysis) strongly affects the structure of the formed polyconjugation system.     

Restricted access chiral stationary phase synthesized via reversible addition-fragmentation chain-transfer polymerization for direct analysis of biological samples by high performance liquid chromatography

Novel hydrophilic microparticles containing β-cyclodextrin (β-CD) were prepared via one-pot synthesis using reversible addition-fragmentation chain-transfer (RAFT) precipitation polymerization, a “controlled/living” radical polymerization technique. The polymerization was initiated by hydrophilic macromolecular chain-transfer agent [poly(2-hydroxyethyl methacrylate), PHEMA]. The hydrophilic PHEMA on the surface of microparticles can well improve their surface hydrophilicity and lead to their biological compatibility. As chiral restricted access material (RAM), the hydrophilic microparticles can be used for determination of enantiomers in biological samples with direct injection via HPLC analysis.     

Controlled radical (co)polymerization of (meth)acrylic esters via the reversible addition-fragmentation chain-transfer mechanism

The homopolymerization of acrylic and fluoroacrylic esters mediated by benzyl dithiobenzoate and dibenzyl trithiocarbonate proceeds in the controlled mode via the reversible addition-fragmentation chain-transfer mechanism, while the controlled radical polymerization of methacrylic esters is not effected under these conditions. The molecular-mass characteristics of the copolymers of acrylic and methacrylic esters may be satisfactorily controlled by benzyl dithiobenzoate-mediated copolymerization when the content of acrylic esters is no less than 50 mol %. If a reversible addition-fragmentation chain-transfer agent active with respect to only one of the monomers is used, compositionally homogeneous narrowly dispersed copolymers are formed via the azeotropic copolymerization of the monomers up to high conversions. The controlled copolymerization of N-vinylpyrrolidone and fluoroacrylates allows the synthesis of alternating narrowly dispersed amphiphilic copolymers with properties different from those of alternating copolymers with a broad molecular-mass distribution.     

Controlled synthesis of copolymers of vinyl acetate and n-butyl acrylate mediated by trithiocarbonates as reversible addition-fragmentation chain-transfer agents

The formation of copolymers of vinyl acetate and n-butyl acrylate via polymerization mediated by di-tert-butyl trithiocarbonate and dibenzyl trithiocarbonate as reversible addition-fragmentation chain-transfer agents is studied. Copolymerization mediated by low-molecular-mass reversible addition-fragmentation chain-transfer agents and by the copolymers formed in their presence proceeds via the pseudoliving mechanism. As a result, the controlled synthesis of narrowly dispersed copolymers of various compositions and desired molecular masses may be implemented. Variation in the compositions of the copolymers with conversion is investigated, and the reactivity ratios of the comonomers are found to differ significantly (r _VA = 0.01 and r _BA = 5.38). Our experimental data make it possible to infer that gradient copolymers are formed in the systems of interest in a wide range of comonomer mixture compositions.     

Reversible addition-fragmentation chain-transfer polymerization: Fundamentals and use in practice

Modern approaches to the synthesis of tailor-made macromolecules by radical polymerization proceeding through the reversible addition-fragmentation chain-transfer mechanism are considered. The mechanism of this process and the experimental and calculation methods for determining its main kinetic parameters are discussed. Particular emphasis is placed on the problems of designing copolymers of various microstructures, including random, gradient, and block copolymers.     

Liquid-crystalline symmetric triblock copolymers

Symmetric fully liquid-crystalline triblock copolymers of various structures containing optically active mesogenic groups are for the first time synthesized via pseudoliving radical reversible addition-fragmentation chain-transfer polymerization. Their phase behavior and physicochemical and optical properties are studied. It is shown that, depending on composition, at low temperatures block copolymers can form at temperatures phase-separated structures caused by microsegregation of blocks of different chemical natures and that, with an increase in temperature, these structures can mix to form a cholesteric mesophase characterized by a helical supramolecular structure. A model illustrating the molecular packing of block copolymers with a phase-separated lamellar structure is advanced. The effect of the molecular structure of the block copolymers on their optical properties is discussed.     

Classical and pseudoliving radical copolymerization of vinyl acetate and acrylic acid in methanol

The homogeneous free-radical copolymerization of vinyl acetate and acrylic acid is studied at 50 and 70°C in methanol with and without the reversible addition-fragmentation chain-transfer agent benzyl dithiobenzoate. It is shown that, under conditions of reversible addition-fragmentation chain-transfer copolymerization, the limiting conversion is 32% and the number-average molecular mass increases linearly with conversion. At the same time, in the absence of the reversible addition-fragmentation reversible chain-transfer agent, the conversion of the monomers amounts to 63% and the molecular mass of the copolymers decreases with conversion.     

Controlled synthesis of styrene and methyl methacrylate copolymers in the presence of reversible addition-fragmentation chain-transfer agents

Molecular-mass characteristics of styrene-methyl methacrylate copolymers formed via the reversible addition-fragmentation chain transfer copolymerization mediated by dithiobenzoates have been studied. Low-molecular-mass reversible-addition fragmentation chain-transfer agents active in the homopolymerization of both monomers and in the homopolymerization of only one of the monomers (styrene) can be used for the controlled synthesis of narrow dispersed copolymers. Conditions for the synthesis of narrow dispersed block copolymers with the desired structure and molecular mass of the blocks have been found. The polymer reversible addition fragmentation chain-transfer agent determines the composition and molecular mass of the first block. The structure of the second block is defined by the composition of the monomer mixture, and the molecular-mass characteristics are set by the concentration of the agent and the conversion of monomers.