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.     

Ternary copolymers of acrylic acid, <Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide,and butyl acrylate: Synthesis and aggregative behavior in dilute solutions

Narrowly dispersed hydrophilic block and random copolymers of acrylic acid and N-isopropylacrylamide of various compositions and molecular masses are synthesized for the first time by controlled radical polymerization via the reversible addition-fragmentation chain-transfer mechanism. The copolymers are used for the synthesis of ternary copolymers with n-butyl acrylate. As shown by dynamic light scattering, the resulting amphiphilic copolymers can form stable dispersions in diluted aqueous solutions. It is found that the effective hydrodynamic radii of dispersion particles may be controlled via variation both in the primary structure of the ternary copolymer, i.e., the amount and sequence of hydrophilic and hydrophobic units, and in the external stimuli, i.e., the temperature and pH of a solution.     

Synthesis of urethane—acrylic multi-block copolymers via electrochemically mediated ATRP

The electrochemically mediated atom transfer radical polymerisation (eATRP) of n-butyl acrylate was investigated under a variety of catalyst concentrations. Poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate) copolymers were prepared via electrochemically mediated atom transfer radical polymerisation (eATRP) using only 7 × 10^?6 mole % of Cu^II complex. The successful chain extension and formation of penta-block copolymers confirmed the living nature of the poly(alkyl acrylates) prepared by eATRP. In this work, the tri-block and penta-block urethane-acrylate copolymers were synthesised for the first time by using tertiary bromine-terminated polyurethane macro-initiators as transitional products reacting with n-butyl acrylate, and subsequently with tert-butyl acrylate in the presence of the Cu^IIBr₂/TPMA catalyst complex. The results of ¹H NMR spectral studies support the formation of tri-block poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate) copolymers, and penta-block poly(tert-butyl acrylate)-block-poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate)-block-poly(tert-butyl acrylate) copolymers.     

Specific features of radical copolymerization of methyl methacrylate and <Emphasis Type="Italic">n</Emphasis>-butyl acrylate in the presence of the tributylborane–<Emphasis Type="Italic">p</Emphasis>-quinone system

Copolymerization of methyl methacrylate (MMA) and n-butyl acrylate (n-BA) in the presence of the tributylborane–p-quinone system has been investigated. Reactivity ratios of the monomers differ from the values known for conventional radical polymerization. The copolymerization proceeds in a controlled manner according to the reversible inhibition mechanism. The nature of p-quinone and the composition of the monomer mixture affect the realization of this mechanism. The microstructure of the copolymers obtained in the presence of borane and p-quinones depends on the nature of the latter.     

Emulsifier-free polymerization of <Emphasis Type="Italic">n</Emphasis>-butyl acrylate involving trithiocarbonates based on oligomer acrylic acid

The effect of the chain length of oligomer acrylic acid obtained in the presence of a low-molecularmass trithiocarbonate and the position of trithiocarbonate fragment (within the chain or at the chain end) on the process of emulsion polymerization of n-butyl acrylate and characteristics of the resulting dispersions has been studied for the first time. It has been found that, when using an oligomer with trithiocarbonate group located within the chain in the emulsion polymerization of n-butyl acrylate in a wide range of monomer–water phase compositions, triblock copolymers self-organizing in aqueous medium to give stable particles with the core–shell structure are formed. Oligomers with M _n ～ (5–10) × 10³ are optimal for synthesis of stable dispersions. In this case, block copolymers with the controlled length of hydrophobic block and a rather narrow MWD may be obtained. Thin films formed from these copolymers retain the structure of the initial dispersions on solvent removal. If the trithiocarbonate group in the oligomer is located at the chain end, the main polymerization product is a diblock copolymer. In this case, the formation of polymer–monomer particles occurs during a longer period of time, the control of MWD is weakened, and the dispersions of particles lose the aggregative stability after thin film formation.     

Controlled synthesis of multiblock copolymers by pseudoliving radical polymerization via the reversible addition-fragmentation chain-transfer mechanism

With the use of two classes of reversible addition-fragmentation chain-transfer agents??dithiobenzoates and trithiocarbonates??multiblock copolymers based on styrene and n-butyl acrylate, which are the best-studied monomers in these processes, are synthesized. It is shown that the polymers containing dithiobenzoate and trithiocarbonate groups are highly efficient for the synthesis of block copolymers, which is independent of the number of stages at which the polymeric RAFT agents are used in polymerization: In all cases, the polymeric RAFT agent is fully consumed in the polymerization of the ??alien?? monomer. The mechanism governing chain formation during the synthesis of multiblock copolymers, that is, the character of monomer insertion into the polymer chain, via one or both ends, is studied. It is found that the order of monomer loading determines the ratio of chains growing through one or two ends. The thermal stability of amphiphilic multiblock copolymers, their solubility in various solvents, and self-organizing ability are investigated.     

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.     

Aggregative behavior of AB and ABC block copolymers in the solid phase and in a nonselective solvent

Effects of the amount of chemically dissimilar blocks (two or three) and their polarity on the aggregative behavior of АВ and АВС linear block copolymers of various compositions that are based on polystyrene, poly(n-butyl acrylate), and either poly(acrylic acid) or poly(tert-butyl acrylate) in bulk and in the nonselective solvent DMF are studied via differential scanning calorimetry and dynamic light scattering. АВ block copolymers composed of two chemically dissimilar blocks in the diluted solution in DMF are fully dispersed into macromolecular coils. However, the simultaneous incorporation of three incompatible blocks of different polarities (polystyrene, poly(acrylic acid), and poly(n-butyl acrylate)) into the copolymer is accompanied by a well-defined segregation of blocks in the nonselective solvent, regardless of the composition of the block copolymer and the length and sequence of blocks. This phenomenon makes itself evident as the formation of intermacromolecular aggregates in diluted solutions with a mean hydrodynamic radius of 60–120 nm that are stable in the range 10–60°C. A decrease in the level of the thermodynamic incompatibility of blocks (replacement of a poly(acrylic acid) polar block with a less polar poly(tert-butyl acrylate) block) or the selective improvement of solvent quality with respect to the polar block (the addition of LiBr to DMF) suppresses the segregation of blocks and may lead to the formation of a molecularly dispersed solution of the block copolymer.     

<Emphasis Type="Italic">In situ</Emphasis> synthesis of block copolymer nano-assemblies by polymerization-induced self-assembly under heterogeneous condition

Controlled synthesis of amphiphilic block copolymer nanoparticles in a convenient way is an important and interest topic in polymer science. In this review, three formulations of polymerization-induced self-assembly to in situ synthesize block copolymer nanoparticles are briefly introduced, which perform by reversible addition-fragmentation chain transfer (RAFT) polymerization under heterogeneous conditions, e.g., aqueous emulsion RAFT polymerization, dispersion RAFT polymerization and especially the recently proposed seeded RAFT polymerization. The latest developments in several selected areas on the synthesis of block copolymer nano-assemblies are highlighted.     

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.     

Effect of the chemical natures of a monomer and a leaving group in symmetric trithiocarbonate as a reversible addition-fragmentation chain-transfer agent on the position of the trithiocarbonate group in macromolecules

The mechanism controlling the formation of polymer chains during the polymerization of vinyl monomers-namely, styrene, 4-vinylpyridine, n-butyl acrylates, and tert-butyl acrylate—mediated by symmetric trithiocarbonates (R-S-C(=S)-S-R) with different leaving groups R is studied. It is shown that the position of the trithiocarbonate fragment in a macromolecule depends on the nature of both the monomer and substituent R in trithiocarbonate. Variations in the structure of the leaving group in the initial reversible addition-fragmentation chain-transfer agent and the synthesis conditions makes it possible to direct polymerization to form a structure (symmetric, end, or asymmetric) relative to the trithiocarbonate group.     

Controlled radical copolymerization of styrene and <Emphasis Type="Italic">tert</Emphasis>-butyl acrylate in the presence of tri-<Emphasis Type="Italic">n</Emphasis>-butylborane–<Emphasis Type="Italic">p</Emphasis>-quinone catalytic system

Radical copolymerization of styrene with tert-butyl acrylate is studied under different conditions. It is found that the addition of tri-n-butylborane or tri-n-butylborane along with p-quinones (2,3-dimethylbenzoquinone, 2,5-di-tert-butylbenzoquinone) results in changes in the relative activities of monomers. Copolymerization in the presence of tri-n-butylborane and p-quinones proceeds via the mechanism of reversible inhibition and is characterized by the linear increase in number-average molecular weight with conversion and by the capacity of copolymers of reinitiation. The hydrolyzed copolymer samples form more stable films compared to copolymers prepared via conventional radical copolymerization.     

Influence of the microstructure of acrylic acid-n-butyl acrylate copolymers prepared by pseudoliving radical polymerization by the reversible addition-fragmentation chain transfer mechanism on their surface activity in aqueous solutions

The influence of the microstructure of acrylic acid-n-butyl acrylate copolymers prepared by pseudoliving radical polymerization by the reversible addition-fragmentation chain transfer mechanism on their surface activity in aqueous solutions was studied. The mechanisms of adsorption of polymer macromolecules on the phase boundary, accounting for the difference in the behavior of the random and block copolymers, were suggested. The dependence of the surface activity on the chain flexibility was elucidated. This dependence is very significant for the random copolymers and insignificant for the block copolymers.     

Aqueous RAFT polymerization of acrylamide: A convenient method for polyacrylamide with narrow molecular weight distribution

Controlled and homogeneous free-radical polymerization of acrylamide(AM) in aqueous phase was realized by using S,S'-bis(α,α'-dimethyl-α'-acetic acid)-trithiocarbonate as a reversible addition-fragmentation transfer(RAFT) agent. Linear increases in molecular weight with conversion and narrow molecular weight distribution were observed for polyacrylamide(PAM) throughout the polymerization. By this method, PAMs with controlled molecular weight(up to 1.0 × 10~6) and narrow molecular weight distribution(M_w/M_n 1.2) were prepared. This study provides an effective method for synthesis of PAMs with narrow molecular weight distribution under environmentally friendly conditions.     

Specific features of the copolymerization of acrylonitrile and acrylamide in the presence of low-molecular-mass and polymeric trithiocarbonates and properties of the obtained copolymers

Regularities of the formation of acrylonitrile-acrylamide copolymers obtained from initial monomer feeds containing 1–50 wt % acrylamide in DMSO solutions with the participation of low-molecular-mass and polymeric trithiocarbonates as reversible addition-fragmentation chain transfer agents are studied for the first time. It is shown that the copolymerization in the presence of low-molecular-mass trithiocarbonates proceeds via a pseudo-living mechanism. The synthesized copolymers prove to be inefficient as reversible addition-fragmentation chain transfer agents, a result that leads to products with bimodal molecular-mass distributions. The rheological characteristics of solutions, as well as the thermal behavior of the copolymers obtained in the absence and in the presence of reversible addition-fragmentation chain transfer agents, are studied. The effect of the synthesis conditions on the properties of the synthesized copolymers is discussed.     

Synthesis of water soluble metalloporphyrin-cored amphiphilic star block copolymer photocatalysts for an environmental application

Two series of water-soluble metalloporphyrin-cored amphiphilic star block copolymers were synthesized by controlled radical polymerizations such as atom transfer radical polymerization (ATRP) and reversible addition fragmentation chain transfer (RAFT), which gave eight amphiphilic block copolymer arm chains consisting of poly(n-butyl acrylate-b-poly(ethylene glycol) methyl ether methacylate) (PnBA-b-PEGMEMA, M_n,GPC = 78,000, M_w/M_n = 1.2, 70 wt% of PPEGMEMA) and poly(styrene-b-2-dimethylamino ethyl acrylate) (PS-b-PDMAEA, M_n,GPC = 83,000, M_w/M_n = 1.2, 67 wt% of PDMAEA), yielding porphyrin(Pd)-(PnBA-b-PPEGMEMA)₈ and porphyrin(Pd)-(PS-b-PDMAEA)₈, respectively. Obtained metalloporphyrin polymer photocatalysts were homogeneously solubilized in water to apply to the removal of chlorophenols in water, and was distinguished from conventional water-insoluble small molecular metalloporphyrin photocatalysts. Notably, we found that the water-soluble star block copolymers with hydrophobic–hydrophilic core–shell structures more effectively decomposed the chlorophenol, 2,4,6-trichlorophenol (2,4,6-TCP), in water under visible light irradiation (k = 1.39 h^?1, t_1/2 = 0.5 h) in comparison to the corresponding water-soluble star homopolymer, because the hydrophobic core near the metalloporphyrin effectively captured and decomposed the hydrophobic chlorophenols in water.     

Linear-Dendritic Block Copolymers Based on <Emphasis Type="Italic">N</Emphasis>-Isopropylacrylamide and Perfluorinated Polyphenylenegermane: Synthesis and Properties at Various Interfacial Boundaries

It is shown that linear-dendritic block copolymers poly(N-isopropylacrylamide)–block–polyphenylenegermane can be prepared by the polymerization of N-isopropylacrylamide in the presence of bis(pentafluorophenyl)germane followed by activated polycondensation with tris(pentafluorophenyl)germane. The properties of the dilute solutions and Langmuir monolayers of the functional polymers and the linear-dendritic block copolymers of N-isopropylacrylamide are studied.     

Synthesis and Characterization of Butyl Acrylate-based Graft Polymers with Thermo-responsive Branching Sites <Emphasis Type="Italic">via</Emphasis> the Diels-Alder Reaction of Furan/Maleimide

Thermo-responsive butyl acrylate/furfuryl methacrylate copolymer-based (PBF backbone) graft (co)polymers with dynamic covalent linkages between their backbones and side chains via the Diels-Alder reaction of furan/maleimide were synthesized. Atom transfer radical polymerization (ATRP) was used to synthesize graft copolymers with thermo-responsive transformation from graft copolymers to linear polymers with bimodal or wide MWD. The NMR measurements indicated that the Diels-Alder reaction and retro-Diels-Alder reaction occurred, depending on the change of the temperature, meaning that the side chains could be cleaved and reformed according to the variation of the temperature. GPC measurements demonstrated that the molecular weights of the polymers were thermoresponsive. Furthermore, three graft copolymers with various branching chains (PBF-g-PBA, PBF-g-P(BMA-co-MA) and PBF-g-PBMA) were compared to study the influence of compatibility between the backbone and the branching chain on the efficiency of Diels-Alder reaction after the cleavage of the DA linkage. The results showed that the ability of the side chains to come back to the main chain was strongly affected by the compatibility between the backbone and the side chains and the flexibility of the polymer chains.     

Synthesis and self-assembly behavior of thermoresponsive triblock copolymer

Block copolymers comprising thermosensitive poly(N-isopropylacrylamide) (PNIPAM) and hydrophobic poly(n-butyl acrylate) (PBA) blocks, were synthesized using the reversible addition-fragmentation chain transfer polymerization (RAFT), their thermosensitive behavior was studied by ultraviolet spectrophotometer (UV) and dynamic light scattering (DLS). The lower critical solution temperature (LCST) was strongly correlated to the hydrophobic/hydrophilic ratio of the copolymers. Their micellization and self-assembly behavior in dilute aqueous solution were studied by surface tension (SFT), DLS and TEM. The resulting block copolymers reversibly formed or deformed micellar assemblies during their LCSTs. The critical micelle concentration (CMC) was controlled by the composition of PBA and PNIPAM, indicating the successful formation of the block copolymers.     

Influence of conditions for preparing butyl acrylate–vinyl butyl ether copolymers using the compensation procedure on their molecular-mass parameters and thickening power in dioctyl sebacate

New butyl acrylate–vinyl n-butyl ether copolymers were synthesized using initiating systems trialkylborane–oxygen, trialkylborane–di-tert-butylperoxytriphenylantimony, and azobis(isobutyronitrile) with compensation dosing of the active monomer. The kind of the initiator does not influence the composition and structure of the copolymers, according to the data of IR and ¹³С NMR spectroscopy, but influences their molecular-mass parameters, according to the data of gel permeation chromatography. The new copolymers dissolved in dioctyl sebacate (synthetic base of lubricating oils) well compete with related imported thickening additives in the thickening effect at temperatures from–40 to 100°С and in the resistance to mechanical degradation. Simple ways to control in the synthesis step the thickening effect of the polymers are suggested.