Effect of fullerene C60 branching center on the conformational properties of arms and the structure of star-shaped polystyrenes in solutions

The effect of the fullerene C₆₀ branching center on the structure and conformation of star-shaped polystyrenes with different arm lengths at equal concentrations in deuterotoluene (c = 1 g/dL) is studied by the method of small-angle neutron scattering. The analysis of neutron scattering for linear PS precursors and stars (the molecular masses of arms are ～7 × 10³ and ～4 × 10⁴) shows that the stars have ～6 arms that form a dense excluded-volume zone around a core inaccessible to other macromolecules. In low-molecular-mass stars (the molecular mass of the arm is ～7 × 10³), strengthening of the static rigidity of arms is observed; as a result, the size of arms increases relative to the size of free PS chains in a good solvent. At a greater length of arms (M ～ 4 × 10⁴), their individual properties are weakly pronounced in the correlation spectrum of the arm because of the interpenetration of arms, thereby demonstrating similarity in the structures of stars and their linear analogs. The mechanism controlling the effect of fullerene C₆₀ on the conformations of stars via solvent structuring by fullerene is discussed.     

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.     

Star-shaped polymers with a doubled fullerene (C60) branching center

Star-shaped regular homopolystyrenes with 22 arms and heteroarm polymers with 12 PS arms and 10 poly(2-vinypyridine) arms have been synthesized by consecutive coupling-functionalization-coupling reactions. The synthesis includes the following stages: the exhaustive grafting of fullerene C₆₀ by polystyryllithium chains (living hexaadducts); the coupling of hexaadducts with the use of dimethyldichlorosilane or 1,4-dibromobutane into twelve-arm macromolecules, where the branching center is composed of two covalently bonded fullerene C₆₀ molecules; functionalization of twelve-arm double-core PS stars during the action of excess dihalides (the replacement of lithium atoms with groups containing chlorine or bromine atoms); and the coupling of living chains of PS or poly(2-vinylpyridine) via reactions with halogen-containing groups at the branching center of double-core PS stars. Linear living polymers used as arms have been prepared by anionic polymerization. Exclusion chromatography has been used to control the individual stages of synthesis. The molecular characteristics of the PS precursor and of star-shaped polymers have been studied in terms of hydrodynamics and light scattering.     

Effect of the branching center structure on self-organization of fullerene-containing star-shaped polystyrenes in deuterotoluene

Small-angle neutron scattering method was used to study self-organization phenomena in regular fullerene-containing star-shaped polystyrenes differing in the number of arms (6 and 12) and branching center structure (one or two covalently bound molecules of C₆₀ fullerene) in deuterotoluene.     

Effect of fullerene C60 as a branching center on molecular and polarization properties of star-shaped polystyrenes

The behavior of molecules of a star-shaped six-arm polystyrene with a covalently bound fullerene C₆₀ as a branching center was studied by viscometry and by measuring the electrooptical Kerr effect and the dielectric polarization in solutions. It was shown that polarization and electrooptical characteristics of a fullerene-containing polystyrene (C₆₀ ～ 3 wt %) differ by an order of magnitude or even greater from the corresponding characteristics of the parent polymer. A comparison of the above properties with the analogous characteristics of the model hexaadduct (the products of reaction between octyllithium and fullerene C₆₀) demonstrated that a difference in the behavior of the star-shaped polystyrene and its parent analog is associated with the structural features of the branching center, among which is the occurrence of six proton addends that are bonded rather weakly to the fullerene cage in the hexaadducts under study.     

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.     

Internal organization and conformational characteristics of star-shaped polystyrene with fullerene C<Subscript>60</Subscript> as a branching center in deuterotoluene

The internal organization of star-shaped polystyrene macromolecules containing fullerene C₆₀ as a branching center is studied via small-angle neutron scattering in deuterotoluene. Analysis of the experimental data according to the Debye-Benoit approximation and the Fourier transformation of the momentum transfer dependences of scattering cross sections for the linear PS precursor and stars is used to determine their molecular masses (9 × 10³ and 5 × 10⁴) and gyration radii (∼2.7 and ∼5.5 nm), the gyration radius of the arm (∼3.4 nm), and the average functionality of the star (5.7). The behavior of scattering cross sections for the fullerene-containing polymer on the whole is described by the law of scattering for stars with Gaussian arms (the Benoit model). However, at the local level (within one chain segment), the fullerene center exerts a specific effect on the conformation of arms. As a result, their statistical flexibility decreases and eventually the size of the star increases by ∼30%. This finding conflicts with the Daoud-Cotton theory.     

Structure formation of fullerene-containing propylene oxide oligomers in deuterium water

Structure formation of propylene oxide oligomers with terminal hydrophobic aliphatic fragment and of oligo(propylene oxides) additionally containing covalently bonded fullerene C₆₀ in deuterium water was studied by small-angle neutron scattering. Propylene oxide chains containing a long hydrophobic fragment undergo organization into spherical micelles, whereas the fullerene(C₆₀)-containing derivatives form rodlike structures (elongated “chains” of cross-linked micelles).     

Structure and supramolecular structures of star-shaped fullerene-containing heteroarm polymers in deuterotoluene

Self-organization of star-shaped polymers containing six PS arms and six polar polymer arms on a common C₆₀ branching center is studied by means of small-angle neutron scattering in deuterotoluene. The results are compared with the corresponding characteristics of six-arm star-shaped fullerene-containing PSs. It is shown that the incorporation of additional polar arms into a six-arm macromolecule leads to its compression due to an increase in the degree of coiling of polar chains in the nonpolar solvent. In solution, heteroarm stars give rise to supramolecular structures in the form of clusters whose dimensions and density depend on the nature of the polar arms. Stars containing PS and poly(2-vinylpyridine) arms are weakly associated, and the mean number of particles in an associate is ∼1.3. Hybrid polymers containing PS and poly(tert-butyl methacrylate) arms demonstrate capability for mutual penetration that favors the appearance of large structures that have a diameter of ∼50 nm and that include up to 12 macromolecules. Hybrid stars containing PS and diblock copolymer (poly(2-vinylpyridine)-poly(tert-butyl methacrylate)) arms exhibit moderate self-organization that manifests itself in the formation of chain associates built from four macromolecules.     

Molecular and hydrodynamic characteristics of star-shaped polystyrenes with one or two fullerene (C<Subscript>60</Subscript>) molecules as a branching center

The molecular properties of regular star-shaped polystyrenes with different numbers of arms (6, 12, and 22) and different structures of the branching center (one or two covalently bonded fullerene C60 molecules) are studied by static light scattering; translational diffusion; and viscometry in toluene, THF, and chloroform. The lengths of the arms for the studied polymer stars are found to be the same. (The molecular mass of the arm is 8.1 × 10³.) The molecular mass and hydrodynamic sizes of macromolecules are estimated. It is shown that the conformational and hydrodynamic characteristics of polymer stars remain practically unchanged on passage from THF to chloroform. Compared to the linear analog, star-shaped fullerene-containing PSs are characterized by a higher density of the molecular coil. The shape of their macromolecules differs insignificantly from spherical, in consistence with theoretical predictions for polymer stars with relatively short arms.     

Neutron Scattering Studies of Structure and Self-Assembly of Star-Shaped Polymers with Fullerene Centres in Solutions

Protonated star-shaped polystyrenes with single and double fullerene C₆₀ core and the hybrid stars with pairs of polar and non-polar arms (tertbuthylmetacrylate, polystyrene) have been studied in deuterated toluene (20 °C) by small-angle neutron scattering at low and moderate polymer concentrations (c₁ ∼ 1 g/dl, c₂ ∼ 3–6 g/dl) to evaluate the peculiarities of fullerene centre action on polymers self-assembly in solutions. As we found, the cores composed of two fullerenes, linked via Si(CH₃)₂-bridge, induce stars' anisotropic interactions and association into chain-like structures (correlation radius ∼400–600 nm). Meanwhile, the single-core stars of polystyrene and hybrids organize globular clusters (size ∼ 10³ nm) those geometry do not change significantly by polymer content variation.     

Gas-separating properties of membranes based on star-shaped fullerene (C<Subscript>60</Subscript>)-containing polystyrenes

Based on regular star-shaped PSs differing in the structure of the branching center (one or two covalently bound fullerene C₆₀ molecules) and in the number of branchings (6 and 12), homogeneous gas-separation membranes have been produced. The transport behavior of the membranes with respect to several gases, such as H₂, He₂, N₂, CO, CO₂, and CH₄, has been studied by mass spectrometry. It has been found that the membranes prepared from six-arm PSs are characterized by a smaller density of macromolecular packing than the membranes obtained from 12-arm PCs and, consequently, they possess higher gas permeability. The starshaped PSs demonstrate a higher selectivity factor for separation of the O₂/N₂ gas pair compared to the corresponding characteristics of the linear PSs. The analysis of gas-separation characteristics by means of the Reitlinger-Robeson diagrams demonstrates that the transport behavior of star-shaped PSs qualitatively surpasses similar parameters of the known polymers in the separation of the CO/N₂ gas pair.     

Structural features and initiating properties of the hexaadduct of polystyryllithium and fullerene C60 in tetrahydrofuran and their role in synthesis of heteroarm star-like polymers

Structural transformations of the hexaadduct of polystyryllithium and fullerene C₆₀ in the course of interaction with a proton donor or 1,1-diphenylethylene and at initiation of styrene polymerization were studied, and their role in the formation of heteroarm star-like polymers with C₆₀ center of branching and arms of polystyrene and poly-2-vinylpyridine was elucidated.     

UV spectroscopy of monosubstituted derivatives of 1,2-dihydro-C60-fullerenes

UV spectroscopy is used to determine the molar absorption coefficients of C₆₀ fullerene and monosubstituted 1,2-dihydro-C₆₀-fullerenes in different solvents. It is found that the extinction coefficient of C₆₀ at 330 nm (the main absorption band most frequently used for qualitative and quantitative determination of the C₆₀ content) is independent of the nature of the solvent and is ～54400 M^?1·cm^?1. The molar absorption coefficients of a series of monosubstituted 1,2-dihydro-C₆₀-fullerenes are practically independent of the chemical structure and the length of the substituent and are 35700 M^?1·cm^?1 (λ ～ 328 nm) and 115250 M^?1·cm^?1 (λ ～ 257 nm). It is shown that the substitution in fullerene proceeds via the double 6,6 bond, as evidenced by the absorption band at 424 nm in the spectra of these compounds, which is characteristic of monosubstituted methanofullerenes.     

Synthesis,Structure, and Properties of the Fullerene C60 Salt of Crystal Violet, (CV+)(C60.−)⋅0.5 C6H4Cl2, which Contained Closely Packed Zigzagged C60.− Chains

The reduction of fullerene C₆₀ by zinc dust in the presence of crystal violet cations (CV⁺) yielded a deep‐blue solution, from which crystals of (CV⁺)(C₆₀^.?) ? 0.5 C₆H₄Cl₂ ( 1 ) were obtained by slow mixing with n‐hexane. The salt contained isolated, closely packed zigzagged chains that were composed of C₆₀^.? radical anions with a uniform interfullerene center‐to‐center distance of 9.98 Å. In spite of the close proximity of the fullerenes, they did not dimerize, owing to spatial separation by the phenyl substituents of CV⁺. The room‐temperature conductivity of compound 1 was 3×10^?2 S cm^?1 along the fullerene chains. The salt exhibited semiconducting behavior, with an activation energy of E_a=167 meV. Spins localized on C₆₀^.? were antiferromagnetically coupled within the fullerene chains, with a Weiss temperature of ?19 K without long‐range magnetic ordering down to 1.9 K.     

Amphiphilic star-shaped polymer with fullerene (C60) branching center and its micelle-forming properties in D2O solutions

Russian Journal of Applied Chemistry - A star-shaped amphiphilic polymer with arms of polystyrene and sodium salt of polymethacrylic acid on the common fullerene (C60) branching center was prepared...     

Direct and initiated halogenation of carbon nanomaterials at low temperatures

Cryochemical reactions of the direct and initiated (by photolysis and radiolysis) halogenation of carbon nanomaterials (C₆₀ fullerene, nanotubes, and nanofibers) at 77–240 K were investigated by the ESR, IR spectroscopy, and elemental analysis techniques. A high reactivity of C₆₀ in reactions with fluorine and chlorine with the formation of corresponding derivatives was shown. High concentrations of radical intermediates indicating the radical chain halogenation of C₆₀ were detected (the kinetic chain length for the chlorination process reaches 10⁴–10⁶ units). The amount of chlorine attached to fullerene is ～35% and practically does not depend on the initiation mode (UV or γ-irradiation at doses up to 350 kGy). The mechanism of the cryochemical halogenation of C₆₀ is considered within the limits of the model of multicenter synchronous transitions in a molecular complex consisting of several reactant molecules including molecular fluorine or chlorine and ensuring a net exothermic effect. The amount of chlorine added to nanotubes and nanofibers did not exceed 2.5–8%, thereby indicating a low reactivity of these materials under cryogenic conditions.     

Compound based on star-shaped oligophenylene and fullerene C60

Compound based on star-shaped oligophenylene and modified with l-valine fullerene C₆₀ has been synthesized and characterized. For characterization, X-ray photoelectron spectroscopy was used.     

Synthesis of star poly(1,3‐cyclohexadiene): Grafting reaction of poly(1,3‐cyclohexadienyl)lithium onto C60

The grafting reaction of poly(1,3‐cyclohexadienyl)lithium onto fullerene‐C₆₀ (C₆₀) was strongly affected by the nucleophilicity of poly(1,3‐cyclohexadiene) (PCHD) carbanions and the polymer chain microstructure, and progressed via step‐by‐step reactions. A star‐shaped PCHD, having a maximum of four arms, was obtained from poly(1,3‐cyclohexadienyl)lithium composed of all 1,4‐cyclohexadiene (1,4‐CHD) units. The rate of the grafting reaction was accelerated by the addition of amine. The grafting density of PCHD arms onto C₆₀ decreased with an increase in the molar ratio of 1,2‐cyclohexadiene (1,2‐CHD) units. The electron‐transfer reaction from PCHD carbanions to C₆₀ did not occur in either a nonpolar solvent or a polar solvent. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3282–3293, 2008.     

Carbon nanotube encapsulated fullerenes: a unique class of hybrid materials

We report the discovery of elongated fullerene capsules contained within single-wall carbon nanotubes, as well as new findings pertaining to encapsulated, self-assembled chains of C₆₀. The observed structures comprise a new, complete class of hybrid materials: hemispherically-capped graphene cylinders of various lengths within carbon nanotubes. Short capsules and chains comprised of only a few C₆₀ molecules spontaneously jump nanometer distances along the axis of the containing tube. A model explaining this behavior is proposed.