Ya. I. Estrin

Properties of nanocomposites based on crosslinked elastomeric polyurethane and ultrasmall additives of single-wall carbon nanotubes

It is shown for the first time that the addition of ultrasmall amounts of single-wall carbon nanotubes leads to a significant increase in the main mechanical characteristics of the crosslinked poly(urethane urea) elastomer. The elastic modulus and the tensile strength pass through maxima as the nanotube concentration is increased from 0 to 0.018 wt %; at a nanotube concentration of 0.002 wt %, the maximum values of the modulus and strength are higher by factors of 2.5 and 1.5, respectively, than the corresponding values for the unfilled polymer. The thermomechanical, spectral, and structural characteristics of nanomodified elastomers are investigated, and possible causes of change in their mechanical parameters are discussed.

EPR Study of Reactivity of Endohedral Metallofullerenes La@C82 and Y@C82

Abstract Reactivity of La@C82 in the mixture with C60 and C70 vs L2pto, phosphoryl radical ∗P(O)(OR)2, and CF3COOH has been studied using EPR spectroscopy. Whereas two former reagents did not change EPR spectrum, treatment with CF3COOH in toluene caused the disappearance of minor octet and a new signal was observed. Similar behaviour was found upon treatment of Y@C82 with CF3COOH. It is interpreted as selective protonation of one isomer of endohedral metallofullerene.

New hyperbranched poly([1,2,3]-triazole-[1,3,5]-triazines)

New hyperbranched polymers have been synthesized through the 1,3-dipolar polycycloaddition of the AB2 monomer—2-azido-4,6-bis(propynyloxy)-[1,3,5]-triazine. The polymers contain conjugated heteroaromatic triazine and triazole cycles and terminal acetylene groups. The products have been characterized by exclusion liquid chromatography and IR and 1H NMR studies.

Study of the influence of single-wall carbon nanotube dispersion techniques upon the properties of epoxy resin-based nanocomposites

A comparison of two techniques, ultrasonication and the controlled wave treatment, for the dispersion of ultra-small concentrations of carbon nanotubes in epoxy resin has been carried out with specially designed instruments. Studies with optical microscopy and physicomechanical and thermomechanical tests showed that both techniques provide almost equal degrees of nanotube dispersion in the matrix and dependences of the basic physicomechanical properties of cured epoxy polymers on the nanofiller concentrations. However, the difference between the two techniques has been shown at the study of the structural properties of the cured epoxy polymers (the molecular weight of the internode chains of the polymeric network, and the vitrification temperature), which are more stable in the case of the wave treatment. Thus, wave treatment is a promising dispersion technique, and it is applicable at the industrial scale because it is almost unlimited by the size and capacities of the equipment.

Calculation of the critical conversion and topological parameters for hyperbranched polyisocyanurate polymers prepared via cocyclotrimerization of mono- and diisocyanates

A new approach to the design of hyperbranched polymers, the cocyclotrimerization of mono-and diisocyanates is proposed. The kinetic scheme for the synthesis of hyperbranched polyisocyanurates was considered and calculated in the generating-function formalism. New theoretical relationships were obtained that make it possible to predict the critical conversion and a change in the structural and molecular-mass characteristics of hyperbranched polyisocyanurates in the course of the reaction, depending on the initial ratio of monoand diisocyanates and on the relative reactivity of isocyanate groups.

Stability and mobility of the endohedral metallofullerene of La@C82 in polycarbonate polymer films

An La@C82-doped polymer (bisphenol-A polycarbonate) was prepared. EPR spectra of La@C82 in a solid polymer film and in a polycarbonate solution in o-dichlorobenzene were studied. The EPR spectrum shape of La@C82 was shown to be sensitive to the phase state of the polymer. La@C82 in the film was found to have a high chemical stability below the glass formation temperature, thus permitting one to use the polymer for the storage and study of endohedral metallofullerenes.

New EPR signals of endohedral metallofullerenes

The EPR spectra of endohedral metallofullerenes (EMF), La-EMF and Y-EMF, which were free of admixtures of C60 and of other empty fullerenes, were examined. Endohedral metallofullerenes were prepared by extraction of fullerene-containing soots with DMF. New signals withg factors close to those of fullerene radical anions were observed in the EPR spectra of solutions of EMF in DMF and DMSO. At −20 °C, these signals are observed as a doublet (ΔHpp≈0.04 mT) and singlet (ΔHpp≈0.01 mT) in solutions of La-EMF and Y-EMF, respectively. These EPR signals belong to solvated La@C82 and Y@C82 molecules and are characterized by small hyperfine interaction constantsaM due to a substantial decrease in the spin density of the unpaired electron at the metal atom.

Synthesis and free-radical polymerization of water-soluble acrylamide monomers

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.

Exchange reactions of urethanes with proton-donating compounds: Kinetics of the reactions of phenyl-N-phenylurethane with butyl alcohols

The exchange reactions of phenyl-N-phenylurethane with aliphatic alcohols, namely, n-butyl, sec-butyl, and tert-butyl alcohols, in ortho-dichlorobenzene and in the media of the corresponding alcohols were studied. In the absence of a catalyst and proton-donating compounds, the monomolecular cleavage of phenyl-N-phenylurethane to isocyanate and alcohol proceeds at a noticeable rate starting only at 250°C. Between 40 and 80°C, the exchange reactions take place via direct exchange between urethane and the photon-donating compound and are second-order up to high conversions (until the almost complete disappearance of the initial urethane). Activation energies and apparent rate constants have been determined for the exchange reactions of phenyl-N-phenylurethane with butyl alcohols. The rates of the exchange reactions in the alcohol medium are compared with those in ortho-dichlorobenzene.

Synthesis of (polycyanoisopropyl)[60]fullerene

The reaction of fullerene with excess 2,2′-azobis(isobutyronitrile) in o-dichlorobenzene at 60°C was studied, and the chemical structure of the reaction product was determined.