Controlled copolymerization of acrylonitrile in bulk via the reversible addition-fragmentation chain-transfer mechanism

The pseudoliving radical binary copolymerization of acrylonitrile with methyl acrylate, styrene, n-butyl acrylate, and tert-butyl acrylate in bulk in the presence of the reversible addition-fragmentation chain-transfer agent dibenzyl trithiocarbonate is performed for the first time. The addition of trithiocarbonate makes it possible to prepare a narrowly dispersed visually optically transparent copolymer in a wide range of monomer-feed compositions even at limiting conversions. Conditions for the synthesis of acrylonitrile copolymers with controlled molecular masses and narrow molecular-mass distributions are ascertained. In the above copolymers, the trithiocarbonate group is shown to be located within the chain.     

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 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.     

Controlled synthesis of styrene-n-butyl acrylate copolymers with various chain microstructures mediated by dibenzyl trithiocarbonate

Copolymers of styrene and n-butyl acrylate are synthesized via pseudoliving radical copolymerization mediated by dibenzyl trithiocarbonate as a reversible addition fragmentation chain transfer agent. In a wide range of monomer feed compositions, narrowly dispersed compositionally uniform copolymers of desired molecular masses are formed, and their gradient structures are controlled by the compositions of the initial monomer feeds. The effects of the compositions, the chain microstructures, and the compositional homogeneity of the copolymers on their glass-transition temperatures are studied.     

Effect of the nature of a solvent on pseudoliving free-radical polymerization of styrene mediated by TEMPO

The kinetics and mechanism of the pseudoliving free-radical polymerization of styrene are studied for the first time under the conditions of reversible inhibition by TEMPO nitroxides. An abnormal decline in the reduced rate of polymerization, which is inconsistent with a decrease in the concentration of the monomer, and an increase in the steady-state concentration of the free nitroxide are discovered. The main quantitative characteristics of the pseudoliving process are determined, namely, the rate constants of reinitiation and reversible recombination, and the constant of pseudoliving equilibrium between dormant and growing chains. It is shown that the polarity of a medium and the concentration of the monomer determine the character of polymerization in a solution: With an increase in the polarity of the solvent, the pseudoliving equilibrium constant increases, the reduced rate of styrene polymerization decreases, and the molecularmass-distribution of the polymer formed at initial conversions narrows. The smaller the concentration of styrene in the reaction system, the more pronounced the above differences associated with the solvent nature.     

Controlled free‐radical polymerization of 2‐vinylpyridine in the presence of nitroxides

Bulk free‐radical polymerization of 2‐vinylpyridine (2VP) in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) was studied under different conditions (temperature and presence of additives). Linear poly‐(2‐vinylpyridine) with a narrow molecular weight distribution and controllable molecular weight was prepared in the presence of acetic anhydride at 95 °C up to a conversion of 66%. At higher conversions side reactions became very important (pseudoliving polymerization). By applying this procedure, well‐defined random copolymers of 2VP with styrene or tert‐butylmethacrylate as well as block copolymers of 2VP with styrene were synthesized. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2889–2895, 2001     

Stable free radical polymerization of n-butyl acrylate in the presence of high-temperature initiators

Living radical polymerizations of acrylate are known to be difficult to achieve using TEMPO as a mediator. The stable free radical polymerization (SFRP) of acrylate tends to stop at low monomer conversion due to the accumulation of TEMPO in the medium as a result of unavoidable bimolecular termination. Rather than solving this problem by destroying the excess nitroxide using ascorbic acid or glyceraldehyde associated with pyridine as reported recently, high temperature initiators were used to slowly and continuously generate new radicals throughout the polymerization to consume the excess TEMPO molecules. Polymerizations of n-butyl acrylate initiated by the alkoxyamine unimer (1-benzoyloxy)-2-phenyl-2-(2′,2′,6′,6′-tetramethyl-1′-piperidinyloxy)ethane (BST) were performed between 130 °C and 134 °C in the presence of a series of high temperature peroxide and azo initiators. The best results in this study were obtained by the continuous addition of small amounts of di-tert-amyl peroxide throughout the polymerization. Under these conditions, the acrylate polymerizations fulfilled the criteria of a controlled polymerization process although the molecular weight distributions were slightly broad (M_w/M_n ∼ 1.5).     

Synthesis of polypeptide/inorganic hybrid block copolymers

Polypeptide/inorganic hybrid copolymers were obtained by a four-step synthetic approach combining (i) atom transfer polymerization of tert-butyl acrylate, (ii) chemical modification of the bromo end groups of ATRP-polymers into primary amino group using Gabriel reaction, (iii) ring opening polymerization of N_ε-trifluoroacetyl-l-lysine or γ-benzyl-l-glutamate N-carboxyanhydrides followed by (iv) the transamidification reaction using a large excess of (3-aminopropyl)trimethoxysilane to substitute the tert-butyl groups of the poly(tert-butyl acrylate) block. Products were characterized using ¹H NMR, FT-IR, DSC and MALDI-TOF MS. These techniques proved that polymerization of tert-butyl acrylate was controlled whatever the molecular weight targeted and that bromide was quantitatively converted to amino end group by a original method leading to the synthesis of copolymers in the presence of N-carboxyanhydrides as monomers. Amphiphilic polypeptide/inorganic hybrid copolymers were then achieved.     

Facile synthesis of thermoresponsive block copolymers of N-isopropylacrylamide using heterogeneous controlled/living nitroxide-mediated polymerizations in supercritical carbon dioxide

A new protocol for preparation of thermoresponsive poly(N-isopropylacrylamide, NIPAM) containing block copolymers is described. It involves two successive heterogeneous controlled/living nitroxide-mediated polymerizations (NMPs) in supercritical carbon dioxide (scCO₂) using N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)]nitroxide (SG1), as the nitroxide. Precipitation NMPs give narrow dispersity macroinitiators (MIs), and a first report of the controlled/living polymerization of N,N-dimethylacrylamide (DMA) in scCO₂ is described. The MI is then used in an inverse suspension NMP of NIPAM in scCO₂ resulting in the efficient preparation of block copolymers containing DMA, tert-butyl acrylate and styrene. Aqueous cloud point temperature analysis for poly(DMA)-b-poly(NIPAM) and poly(acrylic acid)-b-poly(NIPAM) shows a significant dependence on poly(NIPAM) chain length for a given AB block copolymer.     

Polymer micelles from tadpole-shaped amphiphilic block-graft copolymers prepared by “Grafting-through” ATRP

A series of tadpole-shaped block-graft amphiphilic copolymers, i.e., block copolymers consisting of a cylindrical hydrophilic brush block and a coiled hydrophobic block were synthesized using “grafting-through” atom transfer radical polymerization. A tadpole-shaped block-graft copolymer from polystyrene bromide and a methacryloyl-terminated poly(tert-butyl acrylate) was prepared first. Then, hydrolysis of the poly(tert-butyl acrylate) side chains to polyacrylic acid side chains provided tadpole-shaped block-graft amphiphilic copolymers, which formed pH responsive micelles in water, the latter being confirmed by dynamic light scattering and atomic force microscopy.     

Controlled Free-Radical Copolymerization of N-vinyl succinimide and n-Butyl acrylate via a Reversible Addition–Fragmentation Chain Transfer (RAFT) Technique

Summary : Copolymerization of N-vinyl succinimide and n-butyl acrylate in the presence of dibenzyl trithiocarbonate as a reversible addition-fragmentation chain transfer agent was investigated. The linear dependence of molecular mass on conversion and low values of polydispersity index confirmed pseudo-living mechanism of the process. For the first time the soluble copolymers of N-vinyl succinimide and n-butyl acrylate with high composition homogeneity have been synthesized by copolymerization in bulk. The copolymerization kinetics was studied by NMR ¹H spectroscopy; the reactivity ratios were determined: r_VSI = 0.11, r_BA = 2.54. The copolymer microstructure was estimated; it was shown that in conditions of RAFT polymerization gradient copolymers enriched with BA on the tails of the macromolecule and with VSI in the middle can be obtained. The method of elimination of trithiocarbonate fragment by the reaction with an excess of AIBN was proposed leading to formation of the simplest gradient structure of N-vinyl succinimide – n-butyl acrylate copolymer.     

Grafting copolymerization of vinyl monomers on polyimide macroinitiators by the method of atom transfer radical polymerization

Graft copolymers with the main polyimide chain and side chains of poly(n-butyl acrylate), poly(tert-butyl acrylate), poly(methyl methacrylate), poly(tert-butyl methacrylate), polystyrene, and polystyrene-block-poly(methyl methacrylate) were synthesized by atom transfer radical polymerization on the multicenter polyimide macroinitiators in the presence of the halide complexes of univalent copper with nitrogen-containing ligands. Polymerization of metha-crylates is most efficiently developed on the polyimide macroinitiators. The obtained graft copolymers initiate the secondary polymerization (“post-polymerization”) of methyl methacrylate. The conditions of detachment of side chains of graft polymethacrylates that do not involve the ester groups of their monomeric units were found. The molecular mass characteristics of the graft copolymers and isolated polymers, being the detached side chains of the copolymers, were determined. The detached side chains of different chemical structures have low values of the polydispersity index. The procedure developed was used for the preparation of new graft polyimides with side chains of poly-4-nitro-4′-[N-methylacryloyloxyethyl-N′-ethyl]amino-azobenzene that cause the nonlinear optical properties and with the side chains of poly(N,N-dimethylaminoethyl methacrylate) that cause the thermosensitive properties of the copolymers.     

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.     

具有预期结构的苯乙烯与丙烯酸丁酯接枝共聚物的合成与表征

通过苯乙烯 (St)与 4 对氯甲基苯乙烯 (CMS)进行氮氧稳定自由基共聚合反应 ,合成了二元共聚物P(St co CMS) ,并以此共聚物引发丙烯酸丁酯进行原子转移自由基聚合 ,成功地合成了结构明晰的以聚苯乙烯为主链、聚丙烯酸丁酯为支链的接枝共聚物 ,研究了共聚合反应动力学 .P(St co CMS)和接枝共聚物的结构通过1 H NMR得到确认 ,并表征了接枝共聚物平均侧链数目和平均侧链长度     

Visible light-induced synthesis of polysulfone-based graft copolymers by a grafting from approach

The synthesis of polysulfone (PSU) graft copolymers by a two-step “grafting from” approach is described. First, a chlorofunctional PSU (PSU-Cl) is formed via chloromethylation of a commercial PSU. The formed polymers are used macroinitiator for the dimanganese decacarbonyl assisted free-radical polymerization of tert-butyl acrylate, methyl methacrylate, and styrene to give the desired graft copolymers. Moreover, amphiphilic graft copolymers are also formed via posthydrolyzation of poly(tert-butyl acrylate) containing graft copolymers. The intermediates at various stages and the ultimate graft copolymers are characterized by various analysis techniques. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 412–416     

Binary and ternary copolymers of norbornene and its derivatives with acrylates as novel materials for optoelectronics

The free-radical copolymerization of norbornene with methacrylate, tert-butyl acrylate, acrylic acid, and decyl acrylate and the benzoyl peroxide-initiated copolymerization of tert-butyl norbornenecar-boxylate and tert-butyl acrylate are studied for the first time. Novel binary and ternary copolymers are obtained, and experimental conditions (the temperature and time of reaction, initiator concentration, and comonomer ratio) affecting the compositions, molecular masses, glass-transition temperatures, and yields of the copolymers are determined. It is ascertained that the copolymers of norbornene with methyl acrylate and tert-butyl acrylate have high transparency (93?C94%) in the range 300?C800 nm. Because of this fact, the copolymers show promise as matrices for creation of nanocomposite materials suitable for optoelectronic applications.     

Photo-switchable azobenzene-functionalized block copolymers from atom transfer radical polymerizations

Diblock copolymers composed of monomers of tert-butyl acrylate and a side-chain azobenzenecontaining monomer, 4-[(E)-(4-nitrophenyl)diazenyl]phenyl prop-2-enoate were synthesized using atom transfer radical polymerization technique. Experimental strategy involved synthesis of block of tert-butyl acrylate macroinitiator followed by addition of second block of azobenzene-containing monomer to prepare desired block-copolymer. GPC analysis indicated narrow molecular weight distributions with degree of polymerization found in good agreement with targeted value. Prepared block copolymers of varying chain lengths can potentially be used to obtain morphologies that can find useful applications for biomedical applications including intriguing photo-switchable drug delivery systems.     

Synthesis of star polymers via nitroxide mediated free‐radical polymerization: A “core‐first” approach using resorcinarene‐based alkoxyamine initiators

The synthesis of new octafunctional alkoxyamine initiators for nitroxide‐mediated radical polymerization (NMRP), by the derivatization of resorcinarene with nitroxide free radicals viz TEMPO and a freshly prepared phosphonylated nitroxide, is described. The efficiency of these initiators toward the controlled radical polymerization of styrene and tert‐butyl acrylate is investigated in detail. Linear analogues of these multifunctional initiators were also prepared to compare and evaluate their initiation efficiency. The favorable conditions for polymerization were optimized by varying the concentration of initiators and free nitroxides, reaction conditions, etc., to obtain well‐defined star polymers. Star polystyrene thus obtained were further used as macro‐initiator for the block copolymerization with tert‐butyl acrylate. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5559–5572, 2007     

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.     

Comb copolymers of polystyrene-poly(tert-butyl (meth)acrylate) prepared by combination of nitroxide mediated polymerization and photoinduced iniferter technique

Comb copolymers consisting of polystyrene backbone and poly(tert-butyl (meth)acrylate) side chains were synthesized by combination of nitroxide (TEMPO)-mediated polymerization (NMP) and photoinduced grafting from macro-iniferters. First, poly(chloromethylstyrene), PCMS, with the degree of polymerization and two random poly(styrene-co-chloromethylstyrene) copolymers, P(S-co-CMS), with similar but different content (8 and 14 mol%) of CMS units, were synthesized by NMP. In the second step the CMS units both in the homopolymer and the copolymers were converted to N,N-diethyldithiocarbamyl groups (DC) yielding photosensitive multifunctional macro-iniferters. Finally, tert-butyl methacrylate tBuMA was grafted from the synthesized polymer backbones by iniferter technique under UV-irradiation yielding copolymers polystyrene-graft-poly(tert-butyl methacrylate) PS-g-P(tBuMA). Grafting initiated by the macro-iniferters containing ∼6-11 DC initiating sites per macromolecule proceeded by pseudo-living polymerization mechanism, i.e., the number-average molecular weight increased with conversion and the SEC traces were unimodal. In contrast, photo-polymerization initiated by highly functionalized polystyrene backbone was poorly controlled. Hydrolysis of loosely grafted copolymers PS-g-P(tBuMA) afforded amphiphilic copolymers polystyrene-graft-poly(methacrylic acid). Molecular parameters of the synthesized graft copolymers in dilute THF solutions were determined by scattering (DLS, SLS, SAXS) and viscometric measurements.