- [Show abstract] [Hide abstract] ABSTRACT: The effect of additives of copper azomethine complexes of different structure on the character of polycondensation and physicomechanical properties of the obtained metal-containing epoxy polymers was studied. It was shown by the DSC method that the thermal stability of the starting CuII azomethine complexes depended on their structure and nature of polar functional groups. The physicomechanical properties of the unmodified and modified epoxyamine polymers at different ratios of functional groups were compared. The additives of CuII azomethine complexes of 0.42–0.43 wt.% were shown to increase the impact strength of the polymers at the ratio [NH]/EG = 1.07–1.13 (EG is epoxy group).
- [Show abstract] [Hide abstract] ABSTRACT: Dispersions of single-walled carbon nanotubes (SWCNTs) in organic solutions containing poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) were studied by Raman spectroscopy, UV-vis-NIR spectroscopy, and electron microscopy. This polymer interacts with the nanotube resulting in the appearance of a new red-shifted absorption band in the electronic spectrum. This indicates the formation of a charge-transfer complex between MEH-PPV and SWCNTs. Additives of MEH-PPV make it possible to achieve stable suspensions of nanotubes in styrene. A polystyrene/SWCNT/MEH-PPV composite with a high degree of bundle splitting was obtained by polymerization. It was shown that the luminescence intensity of the nanotubes in the Raman spectrum can serve as a indicator for the estimation of the degree of splitting of SWCNT bundles in the composite.
- [Show abstract] [Hide abstract] ABSTRACT: The mechanical and thermomechanical properties of metal-containing epoxy composite films based on silver nanoparticles synthesized in situ are investigated. There is a nonmonotonic dependence of the mechanical properties on the concentration of silver myristate used as a precursor. It is found for the first time that the breaking strength and elastic modulus increase by a factor of 1.8–1.5 relative to those of the unmodified matrix at a small concentration of precursor nanoparticles (on the order of 0.1 wt %). DSC and thermomechanical studies reveal that the glass-transition temperature decreases slightly (by 5–6°C) as the precursor concentration is increased to 0.5 wt %, thereby suggesting a weak plasticization of the modified epoxy matrix. On the basis of the spectrophotometry data measured in the region of surface plasmon resonance of silver nanoparticles (420–425 nm) and SEM data, it is inferred that the in situ strengthening of an epoxy nanocomposite based on epoxy resin ED-20, triethylamine, and silver myristate is attained because silver nanoparticles smaller than 20 nm in size and having a narrow particle-size distribution are formed during curing.
- [Show abstract] [Hide abstract] ABSTRACT: Network copolymer electrolytes were synthesized from polyether (polyester) diacrylates with different structures and chain lengths of polyester diacrylate and polyethylene glycol diacrylate. The optimum matrix for ion transport in the electrolyte was formed from only one type of oligomer. The influence of TiO2 nanopowder additions (∼60 nm) on the conductivity of the copolymer electrolyte was studied. The addition of 10 wt % TiO2 led to an increase in the conductivity by an order of magnitude at 30°C; the effective activation energy decreased by 20%. At elevated temperatures, the mobility of polymer chains increased and the contribution of TiO2 nanoparticles in ion transport was only half of the order of magnitude of the conductivity at 100°C. The increase in the conductivity of the polymer electrolyte after the addition of TiO2 was presumably caused by the formation of a more mobile state of the lithium ion near the nanoparticle surface, as shown by pulsed field gradient (PFG) 7Li NMR.
- [Show abstract] [Hide abstract] ABSTRACT: The physical and mechanical properties of composite materials based on epoxy-amine systems—diglycidyl ether of diphenylolpropane-eutectic mixture of aromatic amines (40 wt % m-phenylenediamine-60 wt % 4,4′-diaminodiphenylmethane) and epoxy-diane resin ED-20-eutectic mixture of aromatic diamines with ultralow contents (≤0.1 wt %) of single-layer carbon nanotubes—are studied. It is shown that, for the concentration dependence of the modulus of elasticity during tension, the additivity rule is obeyed only at the lowest concentrations of carbon nanotubes. In this case, the presence of near-surface layers of a matrix with an increased elastic modulus should be considered.
- [Show abstract] [Hide abstract] ABSTRACT: With the aim to enhance the crack resistance and impact resilience of heat-resistant epoxy polymeric matrices for high-strength composites, modification of epoxy resins with new poly(ether acrylates) and their adducts with amines was studied.
- [Show abstract] [Hide abstract] ABSTRACT: New polymer gel electrolytes based on polyester diacrylates and LiClO4 salt solutions in organic solvents are developed for lithium ion and lithium polymer batteries with a high ionic conductivity up to 2.7 × 10−3 Ohm−1cm−1 at the room temperature. To choose the optimum liquid electrolyte composition, the dependence is studied of physico-chemical parameters of new gel electrolytes on the composition of the mixture of aprotic organic solvents: ethylene carbonate, propylene carbonate, and λ-butyrolacton. The bulk conductivity of gel electrolytes and exchange currents at the gel electrolyte/Li interface are studied using the electrochemical impedance method in symmetrical cells with two Li electrodes. The glass transition temperature and gel homogeneity are determined using the method of differential scanning calorimetry. It is found that the optimum mixture is that of propylene carbonate and λ-butyrolacton, in which a homogeneous polymer gel is formed in a wide temperature range of −150 to +50°C.
- [Show abstract] [Hide abstract] ABSTRACT: Water-soluble acrylamide monomers N-(hydroxymethyl)acrylamide, N-(hydroxymethyl)methacrylamide, N,N-diethanolacrylamide, N,N-diethanolmethacrylamide, N,N-methylethanolacrylamide, and N,N-methylethanolmethacrylamide have been synthesized and characterized. The kinetics and thermodynamics of the free-radical polymerization of these monomers and of the model compounds N-isopropylacrylamide and acrylamide have been studied by the methods of isothermal and scanning calorimetry. The structure and the solubility of the said polymers in water and organic solvents have been investigated and their molecular-mass characteristics and temperatures of glass transition (T g) and melting (T m) have been examined by DSC, liquid chromatography, 1H NMR and IR spectroscopy, and chemical analysis of functional groups. Hydrogels and amphiphilic network polymers based on acrylamide monomers have been prepared and characterized.
- [Show abstract] [Hide abstract] ABSTRACT: The thermodynamics, kinetics, and mechanism of the anionic polymerization of a number of acrylamide monomers has been studied with the use of isothermal and scanning calorimetry, liquid chromatography, 1H NMR and IR spectroscopy, mass spectrometry, and chemical analysis of functional groups. It has been demonstrated that the polymerization system shows the living character and the interchain exchange reactions are absent. It has been shown that N,N-diethanolacrylamide and N,N-diethanol(meth)acrylamide are uninvolved in anionic polymerization. The causes of this phenomenon have been ascertained. The products of the anionic polymerization of acrylamides are hyperbranched copolymers containing heterochain and carbochain fragments. Macromolecules contain end amide and acrylamide groups; in some macromolecules, end tert-butoxide groups of the used polymerization initiator are detected. For the products of the anionic polymerization of the acrylamide monomers under study, the temperatures of glass transition and melting have been measured.
- [Show abstract] [Hide abstract] ABSTRACT: The mechanism of forming the macromonomer based on ɛ-caprolactone and 2-hydroxyethyl methacrylate under the effect of dibutyltin dilaurate has been investigated. The molecular-mass characteristics and the functional-type distribution of the macromonomer have been determined. It has been established that, as the concentration of the methacrylic component is increased, the contribution of side reactions related to its anionic polymerization rises. It has been shown that macromonomers with caprolactone backbones and terminal methacrylic and hydroxyl groups may be obtained. A method has been proposed for the purification of polymerization products from low-molecular-mass impurities, such as dimethacrylates and diols.
- [Show abstract] [Hide abstract] ABSTRACT: New poly(ester di(meth)acrylate)s and poly(esterurethane di(meth)acrylate)s were synthesized by interaction of products of anionic polymerization of 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate with acryloyl chloride, terephthaloyl chloride, and 4,4′-dicyclohexylmethane diisocyanate. By the Michael reaction of the obtained polymeric diacrylates with 4,4′- diaminodicyclohexylmethane, poly(ester di(meth)acrylate)s and poly(ether ester diamine)s with a controlled degree of polymerization containing ether, ester, urethane, and amino groups in each repeating unit of the main chain were synthesized. The structure, the molecular-mass distribution, and the functionality-type distribution of all synthesized polymers were characterized. By free-radical polymerization, polymer networks were prepared from the obtained poly(ester di(meth)acrylate)s and some properties of the networks were determined.
- [Show abstract] [Hide abstract] ABSTRACT: Using the methods of isothermal calorimetry; IR, 1H and 13C NMR spectroscopy; rheokinetics; and exclusion and liquid chromatography under critical conditions, the kinetics of 2-hydroxyethyl methacrylate polymerization initiated by a metallic potassium was studied. It was shown that carbon chain fragments arise through the addition of a carbanion to the double bonds of molecules and the kinetics of this process is determined by competition between reactions of the carbanion with hydroxyl groups and the alkoxide anion with acidic CH groups of an a-carbon atom at the carbonyl group. These reactions define the acid-base equilibrium in polymerizing systems, with the contribution of the radical constituent to the formation of carbochains being negligibly small.
- [Show abstract] [Hide abstract] ABSTRACT: The spontaneous ω-polymerization of 2-hydroxyethyl acrylate proceeding at room and lower temperatures was observed for the first time. A hypothesis concerning the mechanochemical origin of primary free radicals was proposed. These radicals result from multiple freeze-pump-thaw cycles during vacuum degassing of the monomer. The ω-polymerization includes three stages: ripening during which polymerization is absent, formation of separate nuclei as nontransparent white inclusions localized in the bulk, and rapid polymerization of the monomer, accompanied by a significant increase in the reaction volume. It was shown that ω-polymerization can occur in the presence of a nitroxyl radical, an inhibitor of free-radical polymerization. ESR spectroscopy was applied to study the kinetics of consumption of nitroxyl radicals and to estimate the rate of generation of free radicals in spontaneous ω-polymerization.
- [Show abstract] [Hide abstract] ABSTRACT: The anionic polymerization of 2-hydroxyethyl and other acrylate and methacrylates containing mobile hydrogen atoms can be accompanied by an undesirable thermal ω-polymerization. It was shown that this process may be efficiently inhibited by nitroxyl radicals, in particular, 2,2,6,6-tetramethyl-1-piperinyloxy. The effects of concentrations of the inhibitor, oxygen, and dimethylbenzylamine on the kinetics of 2-hydroxyethyl acrylate polymerization and the duration of the induction period were examined. The mechanism of thermally induced polymerization of 2-hydroxyethyl acrylate in the presence of oxygen and dimethylbenzylamine was considered, and reactions leading to accumulation of the crosslinked polymer responsible for ω-polymerization were revealed.
- [Show abstract] [Hide abstract] ABSTRACT: For products arising from the anionic polymerization of 2-hydroxyethyl acrylate, the end-group functionality type distribution was determined by liquid chromatography under conditions close to critical. It was shown that the anionic polymerization of 2-hydroxyethyl acrylate is accompanied by interchain exchange reactions following the transesterification mechanism and by macrocyclization reactions resulting from the intramolecular attack of a growing alkoxide anion at the double bond of its own molecule. The effect of some polymerization conditions on the above reactions was ascertained. To define the role of the intermediate product in the transesterification of esters in the presence of bases, the kinetics of the model reaction of ethyl acetate and sodium ethylate in an ethanol solution containing small amounts of water was investigated. The rate constant of the formation of this intermediate product was estimated; under the conditions of anionic polymerization, this rate constant characterizes the rate of chain termination reaction involving water admixtures.
- [Show abstract] [Hide abstract] ABSTRACT: It was shown that the polymerization of 2-hydroxyethyl (meth)acrylates initiated by alkali metals proceeds through the formation of not only an alkoxide anion resulting from the interaction of a metal with a hydroxyl group but also via an anion-radical arising from the interaction between the metal and the double bond. The process affords a polymer containing commensurable amounts of carbo- and heterochain structures in the backbone. The additives of free-radical polymerization inhibitors completely suppress the formation of carbochain polymer fragments. The initiation of the anionic polymerization of 2-hydroxyethyl (meth)acrylates with mobile hydrogen atoms in the presence of alkali-metal alkoxides occurs via the exchange interaction of the initiator and a hydroxyl group of the monomer and through the direct interaction of the initiator with the double bond. The latter reaction leads to the loss of functionality in the macromolecule being formed. The use of a tert-butoxide anion with the bulky alkyl substituent as an initiator makes it possible to avoid the occurrence of the initiation reaction due to the direct interaction of the initiator with the double bond and to preserve 100% functionality in the resulting macromonomer.
- [Show abstract] [Hide abstract] ABSTRACT: The structure of polymers prepared by the anionic polymerization of 2-hydroxyethyl acrylate and 2-hydroethyl methacrylate was studied using 1H and 13C NMR and IR spectroscopy, liquid chromatography in exclusion and adsorption modes, and chemical analysis of the functional groups. The mechanism of isomerization polymerization yielding polyesters with terminal double bonds and hydroxyl groups was justified. It was shown that the reaction of chain growth involves two stages: the addition of a growing active center (alkoxy anion) to a double bond to give rise to an enolate anion, followed by its reaction with a hydroxyl group via inter- and intramolecular proton transfer and the concurrent regeneration of an ester group and an alkoxy anion. The polymerization of the monomers in question is accompanied by the side chain fragment exchange reaction proceeding by the transesterification mechanism via the adduct of a growing alkoxy anion and ester groups. As a result, the reaction products are composed of not only macromonomers but also of polyester molecules containing both terminal acrylate [poly(ester diacrylates)] and hydroxyl groups [poly(ester diols)].
- [Show abstract] [Hide abstract] ABSTRACT: Kinetics and mechanism of equifunctional 4,4′-(N,N′-bismaleimide)-diphenylmethane/2,2′-diallyl-bisphenol A (BMDM/DABPA) and model (phenylmaleimide/2,2′-diallylphenol) (PMI/AP) systems have been studied in the temperature range 140–400 °C using IR-, 1H- and 13C-NMR spectroscopy, gas chromatography–mass spectrometry GCMS), differential scanning calorimetry (DSC) and isothermal calorimetry. It was established that the cure mechanism consists a unique combination of step-wise and chain polymerization and polycondensation reactions: step-wise “ene” addition reaction of allyl group to maleimide one and consecutive/parallel chain polymerization of maleimide and propenyl groups generated by first reaction. The latter reaction is the main crosslinking reaction. The second source of crosslinking is a dehydration reaction of phenol groups that proceeds with mandatory participation as one of the component 1:1 adduct (product of step-wise polymerization). Homopolymerization of maleimide groups proceeds autocatalytically under the action of free radicals generated by thermal decomposition of maleimide-propenyl groups' donor–acceptor pairs. Steric hindrance in 2,2′-diallyl-bisphenol A prevents the reversible Diels–Alder reaction but this reaction proceeds in model systems. Some thermodynamic and kinetic parameters of the reactions are determined. Copyright © 2003 John Wiley & Sons, Ltd.
- [Show abstract] [Hide abstract] ABSTRACT: A methylated analog of 2,2′-diallylbisphenol A (DABPA) was prepared and characterized by IR and 1H and 13C NMR spectroscopy, elemental analysis, refractometry, and adsorption chromatography. The reactivities of DABPA, 2-allylphenol, and their methylated analogs in the reactions of thermal free-radical polymerization and condensation with 4,4′-(N,N′-bismaleimide)diphenylmethane (BMDM) were compared. For equifunctional systems BMDM-DABPA and BMDM-(DABPA-methylated DABPA, 1:1 mol/mol), the gelation processes were studied and the mechanical properties of the resulting polymers were examined. It was established that the methylated analog of DABPA shows a higher reactivity in thermal free-radical polymerization. This finding made it possible to unequivocally explain the differences in the kinetic and rheokinetic behavior of the tested bismaleimide systems and in the mechanical properties of the related cured polymers.
- [Show abstract] [Hide abstract] ABSTRACT: It was shown that mono- and diacrylates containing proton-donating groups polymerize under the action of alkoxy anions, which are the active sites of anionic polymerization of α-oxides. The kinetic regularities of the process under examination were studied for two model systems (phenylurethaneethylene acrylate-phenylglycidyl ether-dimethylbenzylamine and 2-hydroxyethyl acrylate-phenylglycidyl ether-dimethylbenzylamine). The mechanism of the reaction under study was advanced which includes the transfer of the active site of polymerization to the proton-donating group of a monomer in each event of chain propagation to yield a heterochain polymer (polyester) instead of a carbon-chain one. It was also demonstrated that the polymerization of phenylurethaneethylene acrylate is accompanied by the formation of oxazolidone.
Russian Academy of Sciences
Moskva, Moscow, Russia
- • Institute of the Problems of Chemical Physics
- • Institute of Chemistry