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.     

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 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.     

Microstructure of Polymers Prepared in the Presence of Tri-<Emphasis Type="Italic">n</Emphasis>-butylboron–<Emphasis Type="Italic">p</Emphasis>-Quinone System

The microstructure of polystyrene, poly(methyl acrylate), and poly(tert-butyl acrylate) obtained in the presence of tri-n-butylboron in combination with naphthoquinone-1,4 and 2,3-dimethylbenzoquinone is studied. The stereoregularity of polymers formed under these conditions may be described in the framework of the first-order Markov chain model. The use of p-quinones in combination with tri-n-butylboron favors an increase in the content of isotactic triads in the polymers. The causes of the observed deviations are discussed.     

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.     

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.     

Influence of mixed common solvent on the co-assembled morphology of PS-<Emphasis Type="Italic">b</Emphasis>-PEO and CdS quantum dots

The hybrid structures of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer and inorganic nanoparticles with good stability and biocompatibility have potential applications in drug delivery and bioimaging. Spherical co-assemblies of PS₁₂₀-b-PEO₃₁₈ and oleylamine-capped CdS quantum dots (QDs) are produced successfully in this work by adding water to a mixed common solvent, such as N,N-dimethylmethanamide (DMF)/chloroform, DMF/tetrahydrofuran (THF), or DMF/toluene. The energy dispersive X-ray (EDX) spectrum indicates that QDs are located at the interface between the core and shell of the spherical co-assemblies. The co-assembly process during water addition is traced by transmission electron microscopy (TEM) and turbidity measurement. Spherical co-assemblies are formed through budding from bilayers of the block copolymer and QDs. The morphology of the co-assemblies is related to the miscibility of the QD-dispersing solvents with water and the morphology changes from a spherical to a vesicle-like structure with DMF/toluene. Increasing THF content in the mixed solvent causes morphological transitions from spherical co-assemblies to multi-branched cylinders and micelles where QDs are located in the central core. Increasing chloroform content yields vesicle-like structures with protruding rods on the surface. The mechanism of the morphological transitions is also discussed in detail.     

Chemoselective acylation of monosubstituted thiacalix[4]arene with di-<Emphasis Type="Italic">tert</Emphasis>-butyl dicarbonate

Mono-, di-, and tetrasubstituted derivatives of p-tert-butylthiacalix[4]arene containing tert-butylcarbamate, tert-butylcarbonate, and tert-butyl fragments have been prepared for the first time. Depending on the reaction conditions (reagents ratio, temperature, and the presence of a base), the interaction of the monoamine derivative of p-tert-butylthiacalix[4]arene with di-tert-butyl dicarbonate can lead to the formation of mono-, di-, and tetrasubstituted products.     

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.     

Conformation of block cooligomer macromolecules containing a discotic block

The conformation of block cooligomers that contain a block of eight 2,6,7,10,11-pentapentyloxy-3-(3-acryloylpropyloxy)triphenylene units and a poly(tert-butyl acrylate) block with a length varying from 6 to 300 monomer units was calculated by means of molecular dynamics with the DREIDING force field. The influence of the length of the flexible-chain block of the amorphous polymer on the conformation and structure of the block cooligomer at the level of a single macromolecule was revealed. A tendency toward the screening of the short mesogen-containing block by the flexible-chain polymer block with an increase in its length was demonstrated.     

Synthesis and structure of 2,2′-spirobi(1,3-benzodioxole) derivative prepared from 3,5-di(<Emphasis Type="Italic">tert</Emphasis>-butyl)-1,2-benzoquinone

3,5-Di(tert-butyl)-1,2-benzoquinone reacted with 1,2,3-trimethylbenzimidazolium iodide led to the formation of 2,2′-spirobi[4,6-di(tert-butyl)-1,3-benzodioxole]. The reaction mechanism was suggested. The structure of 2,2′-spirobi[4,6-di(tert-butyl)-1,3-benzodioxole] was established by means of X-ray diffraction analysis.     

Fabrication of polythiophene patterns through blending of a thermally curable polythiophene with poly(methyl methacrylate) and selective thermal curation

In this study, we demonstrate a novel method for fabricating polythiophene patterns, i.e., cylindrical holes and cylinders, through blending of a thermally curable polythiophene carrying with tertiary ester groups (PT-tert-ESTER) and poly(methyl methacrylate) (PMMA), followed by thermal conversion of the PT-tert-ESTER to an insoluble polythiophene via low-temperature cleavage of the tertiary ester groups and removal of the PMMA component via ultraviolet degradation. We show that the surface polarity of substrates, the mass ratio of PT-tert-ESTER to PMMA in the blend solutions as well as the concentration of the blend solutions strongly influence the formation of the polythiophene patterns. Cylindrical holes are more readily formed on less polar substrates when a PT-tert-ESTER dominated blend solution is used, while cylinders are more readily formed on more polar substrates when a PMMA dominated blend solution is used. Moreover, the diameters of both the cylindrical holes and the cylinders decrease as the PT-tert-ESTER concentration is increased in the respective ranges of the PT-tert-ESTER/PMMA ratios where the patterns are formed. Grazing incident X-ray diffraction data have indicated that the patterning of the PT-tert-ESTER component in the blend films improves the crystallinity of PT-tert-ESTER as well as the molecular packing of the insoluble polythiophene in the resultant patterned polythiophene films.     

(Liquid + liquid) equilibria of methanol + ethylbenzene + isooctane + methy <Emphasis Type="Italic">tert</Emphasis>-butyl ether quaternary system at <Emphasis Type="Italic">T</Emphasis> = 303.15 K

Tie line data of {methanol + methyl tert-butyl ether + isooctane} ternary systems were obtained at T = 303.15 K, while data for {methanol + ethylbenzene + isooctane} were taken from literature. The ternary system {methanol + methyl tert-butyl ether + ethylbenzene} and {methyl tert-butyl ether + ethylbenzene + isooctane} were completely miscible. A quaternary system {methanol + ethylbenzene + isooctane + methyl tert-butyl ether} was also studied at the same temperature. In order to obtain equilibium data of the quaternary system, four quaternary sectional planes with several methyl tert-butyl ether/methanol ratios were studied. The effect of the addition of methyl tert-butyl ether on the liquid-liquid equilibrium data of {methanol + ethylbenzene + isooctane} ternary system has been investigate at the same temperature. The distribution curves for ternary and quaternary system was analysed. For the quaternary system {methanol + ethylbenzene + isooctane + methyl tert-butyl ether}, experimental data demonstrated that the distribution coefficient of ethylbenzene between the hydrocarbon and methanol phase on a methyl tert-butyl ether–free basis slightly increases with the increase of methyl tert-butyl ether/methanol ratio. Ternary experimental results were correlated with the UNIQUAC and NRTL equation. The NRTL equation is more accurate than the UNIQUAC equation for the ternary systems studied here. The equilibrium data of three ternary systems were used for determining interactions parameters for the UNIQUAC equation. The UNIQUAC equation fitted to the experimental data appeared to be more accurate than the UNIFAC method for the same quaternary system.     

6,6'-[piperazine-1,4-diylbis(methylene)]bis[3,5-di(<Emphasis Type="Italic">tert</Emphasis>-butyl)-1,2- benzoquinone]: Synthesis and properties

Preparation method is developed for a new 6,6'-[piperazine-1,4-diylbis(methylene)]bis[3,5-di(tert-butyl)- 1,2-benzoquinone], including the stage of 3,5-di(tert-butyl)pyrocatechol aminoalkylation by Mannich reaction followed by oxidation. The molecular structure of one of its hydrolysis products, 4,6-di(tert-butyl)-2,3-dihydroxybenzaldehyde, is established by X-ray diffraction (XRD) analysis.     

Complexation of sodium 2-acrylamido-2-methylpropanesulfonate-monoethanolamine vinyl ether copolymer with polyelectrolytes in aqueous medium

A new water-soluble polyelectrolyte—the copolymer of sodium 2-acrylamido-2-methylpropanesulfonate and monoethanolamine vinyl ether—has been synthesized by free-radical copolymerization. The concentration behavior of the reduced viscosity of copolymer solutions that is typical for polyelectrolytes has been revealed. The reactivity ratios of the monomers have been measured. These values indicate a lower reactivity of monoethanolamine vinyl ether than that of sodium 2-acrylamido-2-methylpropanesulfonate. The complexation of this copolymer with poly(acrylic acid) and poly(N,N-dimethyl-N,N-diallylammonium chloride) has been studied. It has been found that the copolymer demonstrates the polyampholytic behavior and is able to form interpolymer complexes both with polycations and polyanions. It has been established that the polycomplex of the copolymer with polyacrylic acid has the unfolded structure due to the presence of sulfonate groups uninvolved in complexation, while the complex of the copolymer with poly(N,N-dimethyl-N,N-diallylammonium chloride) is compact owing to enhancement of hydrophobic interactions, and the sizes of its species are of the order of 80 nm.     

Nature of solvation effects and mechanism of heterolysis of <Emphasis Type="Italic">tert</Emphasis>-alkyl halides

Specificities of heterolysis of tert-alkyl halides in protic and aprotic solvents were analyzed. Values of log k ₂₅ for heterolysis of tert-butyl chloride, tert-butyl bromide, tert-butyl iodiede, 1-chloro-1-methylcyclopentane, 1-chloro-1-methylcyclohexane, 1-bromo-1-methylcyclopentane, 1-bromo-1-methylcyclohexane, 2-chloro-2-phenylpropane, 1-iodoadamantane, and 2-bromo-2-methyladamantane in 19 to 44 solvents, determined mostly by the verdazyl technique were collected. Correlation analysis of solvation effects was performed in terms of multiparameter equations based on the linear free energy relationship principle, as well as in the logk-E _T coordinates. The nature of solvation effects and mechanism of heterolysis of a covalent C-Hlg bond were discussed.     

Specific Features of Phosphorylation of Per-6-<Emphasis Type="Italic">O</Emphasis>-(<Emphasis Type="Italic">tert</Emphasis>-butyl)(dimethyl)silyl-β-cyclodextrin with Tetraethylphosphorodiamidous Chloride

The pathway of phosphorylation of per-6-O-(tert-butyl)(dimethyl)silyl-β-cyclodextrin with tetraethylphosphorodiamidous chloride significantly depends on the solvent and amine, as well as on temperature. It is possible to choose the phosphorylation conditions ensuring formation of products with prevalence of definite phosphorus functional groups.     

Self-assembly and electrochromic property of electroactive tetraaniline-<Emphasis Type="Italic">b</Emphasis>-PEG diblock copolymer

A kind of amphiphilic rod-coil diblock copolymer consisting both of tetraaniline (TAni) and polyethylene glycol (PEG) blocks, TAni-b-PEG, was synthesized. The diblock copolymer shows excellent electrochromic properties, especially, in switching time and coloration efficiency compared with tetraaniline. TAni-b-PEG is able to self-assemble into spherical structure, which is attributed to the formation of conducting channels and increase of ion-exchange capacity of TAni-b-PEG, implying that a block copolymer with electrochromic block and high ionic conductive block simultaneously possesses improving electrochromic properties.     

Cobalt-catalyzed bisperoxidation of styrenes

A cobalt-catalyzed peroxidation of styrenes with tert-butyl hydroperoxide gives 1-aryl-1,2-bis(tert-butylperoxy)ethanes in up to 53% yields.     

2-Amino-4-bromobutanoic Acid

(2S)- and (2R)-2-Amino-4-bromobutanoic acid were prepared starting from N-Boc-glutamic acid α tert-butyl ester. The double tert-butyl protection was necessary to prevent a partial racemisation during Barton’s radical decarboxylation used to transform the γ-carboxylic group into a bromide. This bromide reacted with different nitrogen, oxygen and sulphur nucleophiles to give nonnatural amino acids characterised by basic or heterocyclic side chains. The title compound was also used to prepare a conformationally constrained peptidomimetic.