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.     

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.     

Synthesis of tertiary-butyl acrylate polymers and preparation of diblock copolymers using atom transfer radical polymerization

The synthesis of tert-butyl acrylate by atom transfer radical polymerization (ATRP) is reported. This polymer was prepared using FeCl₂ · 4H₂O(PPh₃)₂ catalyst system in conjunction with methyl 2-bromopropionate as initiator, in bulk and in solution using acetone as a solvent. The addition of solvent was necessary in order to decrease the polymerization rate and to afford low polydispersity polymers. The number-average molecular weights of the resulting polymers increased in direct proportion to the monomer conversion, and the polydispersities (M_w/M_n) were as low as 1.2. In addition, the preparation of an AB diblock copolymer of poly (n-butyl methacrylate)-block-poly (tert-butyl acrylate) by ATRP is reported. The resulting polymers and copolymers were characterized by means of size exclusion chromatography and ¹H-NMR Spectroscopy.     

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.     

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.     

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.     

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.     

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.     

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.     

Synthesis of gradient copolymers of styrene and tert-butyl acrylate by pseudoliving radical polymerization mediated by the reversible inhibitor TEMPO

The gradient copolymers of styrene and tert-butyl acrylate are synthesized by pseudoliving free-radical polymerization in the presence of TEMPO. Despite the inability of tert-butyl acrylate to undergo polymerization in the presence of the nitroxide TEMPO, the introduction of styrene makes it possible to perform the process under the controlled reversible-inhibition regime. The introduction of an additional high-temperature initiator, cumene hydroperoxide, increases the yield of the copolymer, while the pseudoliving mechanism of the process is preserved. This phenomenon is confirmed by the facts that the concentration of nitroxide remains almost invariable during polymerization and that the molecular mass of the polymerization product increases with conversion. Variations in the composition of the copolymer and its molecular mass during polymerization are evidence that the gradient copolymers are formed.     

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.     

Synthesis of starlike PtBA‐g‐PEO amphiphilic graft copolymer via highly efficient Cu‐catalyzed SET‐NRC reaction at ambient temperature

Two new amphiphilic star graft copolymers bearing hydrophobic poly(tert‐butyl acrylate) backbone and hydrophilic poly(ethylene oxide) (PEO) side chains with different molecular weights were synthesized by sequential reversible addition fragmentation chain transfer (RAFT) polymerization and single electron transfer‐nitroxide radical coupling (SET‐NRC) reaction under mild conditions. RAFT homopolymerization of tert‐butyl 2‐((2‐bromopropanoyloxy)methyl)acrylate was mediated by a four‐armed chain transfer agent in a controlled way to afford a well‐defined starlike backbone with a narrow molecular weight distribution (M_w/M_n = 1.26). The target poly(tert‐butyl acrylate)‐g‐PEO (PtBA‐g‐PEO) star graft copolymers were synthesized by SET‐NRC reaction between Br‐containing PtBA‐based starlike backbone and PEO end functionalized with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) group using copper/N,N,N′,N′,N″‐pentamethyldiethylenetriamine as catalytic system at ambient temperature via grafting‐onto strategy. The critical micelle concentration values of the obtained amphiphilic star graft copolymers in aqueous media and brine were determined by fluorescence probe technique using pyrene as probe. Diverse micellar morphologies were formed by varying the content of hydrophilic PEO segment as well as the initial concentration of stock solution. In addition, poly(acrylic acid)‐g‐PEO double hydrophilic star graft copolymers were obtained by selective acidic hydrolysis of hydrophobic PtBA starlike backbone without affecting PEO side chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

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 polymerization of methacrylates of various structures in the presence of the AIBN-FeCl3-N,N-dimethylformamide catalytic system

The controlled radical polymerization of methyl methacrylate, 2-ethoxyethyl methacrylate, and tert-butyl methacrylate conducted via atom-transfer radical polymerization in the presence of the AIBN-FeCl₃· 6H₂O-N,N-dimethylformamide catalytic system is studied. For all the systems under study, the rate of reaction is first order with respect to the monomer concentration. The number-average molecular mass of the polymers linearly increases with conversion, and their polydispersity indexes are below 1.6. The rate of polymerization decreases in the following sequence: 2-ethoxyethyl methacrylate > methyl methacrylate > tert-butyl methacrylate. The presence of ω-terminal chlorine atoms in polymer macromolecules is confirmed by ¹H NMR spectroscopy and through the block copolymerization of methyl methacrylate with a poly(ethoxyethyl methacrylate)-based macroinitiator.     

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.     

Homo and block copolymers of tert-butyl methacrylate by atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) of tert-butyl methacrylate (tBMA) was investigated using cuprous bromide with different ligands, solvents, deactivators, etc. The polymerization in bulk and diphenyl ether solvent system performed using Cu(I)Br complexed with N, N, N′, N″, N″-pentamethyldiethylenetriamine (PMDETA) catalyst in conjunction with 2-bromopropionitrile as an initiator at room temperature showed a curvature in the first-order kinetic plot. The controlled polymerization in methanol solution resulted in slower rate of polymerization and lower molecular weights. Well-defined diblock copolymers of PSt-b-PtBMA synthesized by polystyrene bromo macroinitiator (PSt-Br) with Cu(I)Cl/PMDETA catalyst system yielded predetermined molecular weights and lower polydispersities. Otherwise, the Cu(I)Br/PMDETA catalytic system showed an inefficient polymerization of tert-butyl methacrylate with lower molecular weights and higher polydispersities. Subsequent hydrolysis of the homopolymer refluxed in dioxane with addition of HCl afforded well-defined poly(methacrylic acid).     

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     

Directional Synthesis of Hybrid Polymers from 2- and 4-Vinylpyridines

Formation of hybrid three-dimensional structures by treatment of copolymers of 2- and 4-vinylpyridine with butyllithium, followed by grafting of tert-butyl acrylate molecules, was studied by mass-spectrometric thermal analysis and ¹³C NMR spectroscopy.     

N-substitution of polybenzimidazoles: Synthesis and evaluation of physical properties

Series of N-substituted polybenzimidazoles (PBI) were synthesized using selective alkyl groups with varying bulk and flexibility, viz., methyl, n-butyl, methylene trimethylsilane and 4-tert-butylbenzyl. PBI-I based on 3,3′-diaminobenzidine (DAB) and isophthalic acid and PBI-BuI based on DAB and 5-tert-butyl isophthalic acid were chosen for N-substitution. Structural characterizations of substituted polymers by FT-IR and ¹H NMR revealed elimination of hydrogen bonding. Evaluation of their physical properties revealed that N-substitution rendered better solvent solubility in common organic solvents, more open polymer matrix, but reduced thermal properties in comparison to their respective parent PBI. 4-tert-butylbenzyl, methylene trimethylsilane or n-butyl group substituted polymers were soluble even in chlorinated solvents (CHCl₃ and TCE). Substantial variations in gas permeability of inert gases, He and Ar and attractive P_He/P_Ar selectivity, especially after methyl group substitution depicted potential of these materials for gas separation.     

Synthesis and characterization of novel resorcinarene‐centered amphiphilic star‐block copolymers consisting of eight ABA triblock arms by combination of ROP,ATRP, and click chemistry

Novel amphiphilic eight‐arm star triblock copolymers, star poly(ε‐caprolactone)‐block‐poly(acrylic acid)‐block‐poly(ε‐caprolactone)s (SPCL‐PAA‐PCL) with resorcinarene as core moiety were prepared by combination of ROP, ATRP, and “click” reaction strategy. First, the hydroxyl end groups of the predefined eight‐arm SPCLs synthesized by ROP were converted to 2‐bromoesters which permitted ATRP of tert‐butyl acrylate (tBA) to form star diblock copolymers: SPCL‐PtBA. Next, the bromide end groups of SPCL‐PtBA were quantitatively converted to terminal azides by NaN₃, which were combined with presynthesized alkyne‐terminated poly(ε‐caprolactone) (A‐PCL) in the presence of Cu(I)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine in DMF to give the star triblock copolymers: SPCL‐PtBA‐PCL. ¹H NMR, FTIR, and SEC analyses confirmed the expected star triblock architecture. The hydrolysis of tert‐butyl ester groups of the poly(tert‐butyl acrylate) blocks gave the amphiphilic star triblock copolymers: SPCL‐PAA‐PCL. These amphiphilic star triblock copolymers could self‐assemble into spherical micelles in aqueous solution with the particle size ranging from 20 to 60 nm. Their micellization behaviors were characterized by dynamic light scattering and transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2905–2916, 2009