Hydrodynamic and electrooptical properties of star-shaped heteroarm fullerene (C60)-containing polymers in solutions

Star-shaped heteroarm polymers with a C₆₀ branching center and polystyrene and poly(2-vinylpyridine) arms of equal molecular masses have been studied by the methods of molecular hydrodynamics (translational diffusion and viscometry) and electrooptics (the Kerr effect). The experimental hydrodynamic data are interpreted in terms of the regular star model. The molecular masses and hydrodynamic sizes of star-shaped heteroarm polymers in solutions are estimated. A comparison of these values with the corresponding parameters of linear polymer-analogs (polystyrene and poly(2-vinylpyridine)) makes it possible to characterize the branching degree of macromolecules. The study of the electrooptical properties of the heteroarm polymer in benzene demonstrates the tendency of macromolecules toward aggregation.     

Thermal degradation of a heteroarm starlike polymer with fullerene C60 core

The mechanism of thermal degradation of a 12-arm starlike polymer with fullerene C₆₀ core and equal number of polystyrene and poly(tert-butyl methacrylate) arms was studied by thermal desorption mass spectrometry. Thermal characteristics of the heteroarm stars were compared with those of six-arm starlike fullerene-containing polystyrenes and linear poly(tert-butyl methacrylate).     

Characteristics of fullerene C60-doped polymers

The results of studying the characteristics of various polymers that possess different structures and are used for various applications after their modification by minor amounts of fullerene C₆₀ are summarized. The character of bonds that arise in fullerene-doped polymer compositions is considered. Mechanical, physicochemical, and physical characteristics of fullerene-containing polymers that show promise for modern technologies are described. The reasons for improving the performance of fullerene-containing polymers are analyzed.     

Star-shaped polymers with the fullerene C60 branching center

The anionic methods for the synthesis of homo- and heteroarm (hybrid) star-shaped polymers using fullerene C₆₀ aPre considered. The possibilities of fullerene C₆₀ as an agent of combination of living polymer chains and the procedures of transformation of polymer derivatives of C₆₀ (hexaadducts) into polyfunctional macroinitiators of anionic polymerization of vinyl monomers are shown. The methods for functionalization of polymer fullerene derivatives and their combinations into structures of complex controlled architecture are presented. The structural features and initiating properties of the living polymer fullerene derivatives and their role in the formation of heteroarm star-shaped macromolecules with the controlled number of branches and predetermined molecular weight characteristics of the arms are discussed. The hydrodynamic properties of the star-shaped fullerene-containing polymers are considered. The data on the small-angle neutron scattering study of self-organization of the stars in solutions are presented.     

Anionic synthesis of polystyrene and polybutadiene heteroarm star polymers

The use of living linking reactions of poly(styryl)lithium with 1,3-bis(1-phenylvinyl)benzene followed by crossover reactions with styrene or butadiene monomers has been used to prepare four-armed heteroarm, star-branched polymers. Bimodal molecular weight distributions have been observed for crossover reactions with both styrene and butadiene. Addition of THF ([THF]/[Li]=14–32) for crossover to styrene and lithium sec-butoxide for crossover to butadiene produces monomodal molecular weight distributions. Symmetrical, four-armed star polystyrenes have been synthesized; properties have been compared with a corresponding polymer prepared via a silicon tetrachloride linking reaction. Heteroarm, star-branched polymers with two polystyrene arms and two polybutadiene arms with high 1,4-microstructure have been prepared.     

Structural features of star-shaped fullerene (C60)-containing polystyrenes: Neutron scattering experiments

Structural features of star-shaped polyprotostyrene and polydeuterostyrene containing fullerene C₆₀ as a branching center have been studied by small-angle neutron scattering in benzene solutions. The results are compared with the corresponding characteristics of linear PSs, the molecular mass of which is equal to the molecular mass of one star arm in star-shaped macromolecules. The molecular masses of star-shaped polymers are estimated, and their branching center is shown to be hexafunctional. At relatively low concentrations of starshaped polymers in solutions, one can observe excluded volume effects, which are related by the presence of regions with higher densities at the center of a macromolecule. Using the Fourier transform of the scattering cross section, three-dimensional correlation functions are obtained, and the regular structure of stars is proved. Conclusions about the local correlations of units within one star arm and averaged correlations between units of neighboring arms within a given star are derived. An analysis of three-dimensional correlations shows that the centers of mass of all star arms are directed along orthogonal axes passing through the C₆₀ branching center of a star-shaped macromolecule.     

Synthesis and properties of water-soluble derivatives of fullerene C60

Procedures for synthesized of water-soluble forms of fullerene C₆₀ and its derivatives were developed.     

Phosphorylated azahomo[60]fullerene: synthesis and electrochemical properties

A reaction of [60]fullerene with O,O-dibutyl azidophosphate affords a first representative of phosphorylated azahomo[60]fullerenes, which is easier to reduce electrochemically than the starting C₆₀.     

Synthesis and stability of linear and star polymers containing [C60] fullerene

Linear and symmetric star block copolymers of styrene and isoprene containing [C₆₀] fullerene were synthesized by anionic polymerization and appropriate linking postpolymerization chemistry. In all block copolymers, the C₆₀ was connected to the terminal polyisoprene (PI) block. The composition of the copolymers was kept constant (～30% wt PI), whereas the molecular weight of the diblock chains was varied. The polymers were characterized with a number of techniques, including size exclusion chromatography, membrane osmometry, and ¹H NMR spectroscopy. The combined characterization results showed that the synthetic procedures followed led to well‐defined materials. However, degradation of the fractionated star‐shaped copolymers was observed after storage for 2 months at 4 °C, whereas the nonfractionated material was stable. To further elucidate the reasons for this degradation, we prepared and studied a four‐arm star copolymer with the polystyrene part connected to C₆₀ and a six‐arm star homopolymer of styrene. These polymers as well as linear copolymers end‐capped, through ? N<, with C₆₀ were stable. Possible reasons are discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2494–2507, 2001     

Influence of fullerene C60 on the structure and mechanical properties of polyethylene

Influence of fullerene C₆₀ on the structure and mechanical properties of low-density polyethylene samples cast from a melt and a solution was studied.     

Cytotoxicity of doxorubicin conjugated with C60 fullerene. Structural and in vitro studies

Structural Chemistry - Conjugating an anticancer drug of high biological efficacy but large cytotoxicity with a “transporting” molecule of low toxicity constitutes a valuable approach...     

Thermochemistry of C60 and C70 fullerene solvates

In an effort to improve understanding of dissolution behaviour of fullerenes and their simple chemical derivatives the binary systems of C₆₀, C₇₀ and the piperazine monoadduct of [60] fullerene C₆₀ N₂C₄H₈ with a series of aromatic solvents have been studied by means of DSC. In certain systems solid solvates have been found to be the thermodynamically stable phases relative to saturated solution at room temperature. Identified solid solvates were characterized by their compositions, temperatures and enthalpies of incongruent melting transitions. The regularities in thermodynamic stability of the solvated crystals have been discussed along with dissolution properties of fullerenes and the derivative. Certain correlations have been observed.     

Theoretical study on the chiroptical optical properties of chiral fullerene C60 derivative

Time-dependent density functional theory (TDDFT) calculations have been used to investigate UV/CD spectra and nonlinear optical (NLO) property of the C(60)-fullerene bisadduct (R,R,(f,s)A)-[CD(+)280] for the first time. The electron transition natures of the four main measured bands are analyzed, and their results are used to designate the excited states involved in an electron-transfer process of the studied compound. On a comparative scale, the predicted excitation energies and oscillator strengths are in reasonable agreement with the observed values, demonstrating the efficiency of TDDFT in predicting the localized and charge transfer transitions. The good agreement between the experimental and the simulated CD spectra shows that TDDFT calculations can be used to assign the absolute configurations (ACs) of chiral fullerene C(60) derivatives with high confidence. The observed large dissymmetry ratio g (g = Δε/ε) at about 700 nm results from the orbital characters of the local fullerene excited state, which leads to large transition magnetic dipole moment and small transition electronic dipole moment. The different functionals and solvent effects on UV/CD spectra were also considered. The studied compound has a possibility to be an excellent second-order NLO material from the standpoint of transparency and large second-order polarizability value.     

Thermodynamic properties of fullerene C60 solutions in a mixture of tetrachloromethane and toluene

The solubility of fullerene C₆₀ in the tetrachloromethane-toluene system is measured over the entire range of compositions of the mixed solvent in the temperature range 298.15–338.15 K. An equation is proposed for describing the solubility of C₆₀ as a function of the temperature and the composition of the mixed solvent. The equation is used for calculating the thermodynamic characteristics of solution of the fullerene. It is found that, in the investigated C₆₀-CCl₄/C₆H₅CH₃ system, two types of solid solvates of the fullerene with the solvent are formed. The enthalpies and temperatures of incongruent melting of the crystalline solvates are determined by differential scanning calorimetry. The thermodynamic characteristics of solution and solvation of C₆₀ in CCl₄ and C₆H₅CH₃ are obtained. It is shown that the entropy factor plays a decisive role in the temperature dependence of the Gibbs energy of solvation of the fullerene.     

Phase equilibria in the system fullerene C60-hexane-o-xylene-dimethylformamide

Phase diagrams in ternary liquid systems hexane o-xylene DMF were studied at 298.15 333.15 K. Critical points in these systems were determined. The fullerene C₆₀ distribution in the ternary liquid systems with constant and variable compositions of two organic phases was studied at variable fullerene concentration.     

The use of solid phase synthesis for the preparation of monoadducts of fullerene C60

The method of solid phase synthesis was proposed for the preparation of monoadducts of fullerene C₆₀ using 3′H-cyclopropa[1,9](C₆₀-I _h )[5,6]fullerene-3′-carboxylic acid as an example.     

Formation of secondary fullerene ozonides in the ozonolysis of C60 solutions and chemiluminescence upon their hydrolysis

The formation of secondary fullerene ozonides (SFOs) in the ozonolysis of C₆₀ solutions in CCl₄ has reliably been determined for the first time; SFOs are accumulated during the whole ozonolysis time as a suspension in CCl₄. Hydrolysis of the SFOs results in chemiluminescence (CL) (I _max = 2.65·10⁸ photon s⁻¹ mL⁻¹), whose spectra contain maxima at 558, 608, and 685 nm. The most probable CL emitters are excited fullerene polyketones. Hydrogen peroxide was identified as a stable hydrolysis product of the SFOs by the color reaction with diphenylcarbazide and CL arisen upon the addition of an aqueous solution of FeSO₄·9H₂O to the hydrolyzate of the SFO. Chemiluminescence upon hydrolysis is a selective test for SFOs and allows one to find them in a complex mixture of the ozonolysis products of C₆₀. The rate constant and activation energy of SFO hydrolysis were determined from the kinetic measurements of CL. For SFO hydrolysis several probable reactions were proposed, including the formation of the CL emitters, and their heat effects were estimated using the PM3/RHF and AM1/RHF semiempirical methods for one-and two-cage model structures of SFOs. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1322–1329, August, 2006.     

Structural aspects in polymers: interconnections between conformational parameters of the polymers with their physical properties

This article focuses on the influence of the geometric structure of the polymer chain on the physical properties of polymers. It is shown that for polyheteroarylenes the Kuhn segment calculated based on the geometric structure of the polymer chain has a good correlation with the physical properties of those polymers. For aliphatic polymers, a volume factor is suggested that equals the ratio of the Van der Waals volume of pendant substitute to the volume of the whole polymer chain. It is shown that the properties of aliphatic polymers that depend on free volume are well described by this value.     

Comparison of electrochemical properties of two-component C60-Pd polymers formed under electrochemical conditions and by chemical synthesis

The electrochemical behavior of C₆₀-Pd polymer formed under electrochemical conditions and by the chemical synthesis was examined. In these polymers, fullerene moieties are covalently bonded to palladium atoms to form a polymeric network. Both materials deposited at the electrode surface show electrochemical activity at negative potentials due to the reduction of fullerene cage. Electrochemically formed thin polymeric films exhibit much more reversible voltammetric response in comparison to chemically synthesized polymers. The morphology and electrochemical behavior of chemically synthesized C₆₀-Pd polymer depend on the composition of grown solution. Chemical polymerization results in formation of large, ca. 50 μm, crystallic superficial structures that are composed of regular spherical particles with a diameter of 150 nm. The capacitance properties of C₆₀-Pd films were investigated by cyclic voltammetry and faradaic impedance spectroscopy. Specific capacitance of chemically formed films depends on the conditions of film formation. The best capacitance properties was obtained for films containing 1:3 fullerene to Pd molar ratio. For these films, specific capacitance of 35 Fg^?1 was obtained in acetonitrile containing (n-C₄H₉)₄NClO₄. This value is much lower in comparison to the specific capacitance of electrochemically formed C₆₀-Pd film.