O. V. Ratnikova

Degradation of Macromolecular Chains in Fullerene C60–Polystyrene Composites

Fullerene C60–polystyrene composites prepared by mixing benzene solutions of polystyrene and of C60 with subsequent lyophilization have been studied by hydrodynamic and optical methods. The distributions of effective hydrodynamic radii of polystyrene samples within a wide range of molecular weights have been compared to those of composites with fullerene by size exclusion chromatography in tetrahydrofurane. Simultaneously, under real conditions in a porous system of chromatographic columns with the medium (tetrahydrofurane), in which fullerene is virtually insoluble, the possibility of fullerene transport by polymer molecules because of the formation of the C60‐polystyrene molecular complex was investigated. Comparative analysis of spectra of composites, mixtures of polystyrene and fullerene as well as spectra of fullerene‐containing star‐shaped polystyrenes, in which the fullerene core is covalently bound to polystyrene arms, was carried out by UV spectroscopy. The experimental data suggests that during the preparing of composites and their subsequent dissolution the degradation of polystyrene chains occurs with the formation of a covalent bond between chain fragments and fullerene. A qualitative mechanism of polystyrene macromolecules degradation has been proposed.

Effect of Centrifugal Field upon Hydrodynamic Characteristics of Fullerene C60 and Poly(N-vinylpyrrolidone) Complex in Aqueous Solutions

Abstract Velocity ultracentrifugation method was employed to study aqueous solutions of fullerene C60 and poly(N-vinylpyrrolidone) complex (PVP-C60). Strong dependence of sedimentation coefficient S 0 on ultracentrifuge rotor speed n was found. The S 0 value increases as the value of n decreases from that corresponding to isolated PVP-C60 macromolecules to the value that the clusters of PVP-C60 (registered by the light-scattering method) would have at n → 0. This dependence indicates that molar mass and size of clusters change depending on the centrifugal field applied.

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 and Tribological Properties of Fullerene‐Containing Composite Systems. Part 3. Features of the Mechanism of Thermal Degradation of Poly‐(N‐Vinyl‐Pyrrolidone) and Its Compositions with Fullerene C60

By mass‐spectrometric thermal analysis (MTA) the thermochemical features of poly(N‐vinyl pyrrolidone) (PVP) and its compositions with fullerene C60 were studied. The mechanism of PVP thermal degradation was investigated; in particular the nature of the low‐temperature degradation (between 75 and 300°C) accompanied by output of pyrrolidone was explained as well as the influence of fullerene C60 on this mechanism. It was shown that during thermal degradation of copolymer PVP‐C60, there is a disappearance of the low‐temperature peaks of the output of pyrrolidone that is interpreted as an increase of the thermal stability of N‐vinyl‐pyrrolidone fragments in this product in comparison with their thermal stability in pure PVP.

The New Method for the Synthesis of Fullerols Based on Radical Reaction

Abstract The method for the synthesis of fullerols C60(OH) x was developed, allowing to obtain products with low number of hydroxy groups attached to fullerene molecule. At the first stage, product C60(tert‐BuO) x was obtained by the radical reaction of C60 with tert‐butyl‐peroxide under heating or UV‐irradiation. At the second stage, fullerol C60(OH) x was synthesized after the elimination of tert‐butyl groups by acid treatment. Several samples C60(OH) x containing different numbers (x = 2–5) of hydroxy groups were obtained, the main product had x = 2. The structure of the fullerols was confirmed by UV‐ and Fourier‐transform infrared (FTIR)‐spectroscopy and MALDI‐TOF mass‐spectrometry.

Structure and Hydrodynamical Properties of Heteroarm Star‐Shaped C60 Fullerene‐containing Polymers

Multifunctional initiator with six active centers for anionic polymerization of polar vinyl monomers based on hexaadduct of polystyryllithium with C60 fullerene was obtained. Star‐shaped polymers with fullerene C60 as branching center and polystyrene and poly‐(2‐vinylpyridine) arms were synthesized using anionic polymerization techniques; the conditions of modification of macroinitiator (hexaadduct of polystyryllithium with fullerene C60) were varied. Translational diffusion and viscometry in benzene solutions were used to determine molecular masses and functionality (f) of heteroarm molecules. It was shown that during the formation of heteroarm macromolecules, the determining stage is the process of modification of hexaadduct with 1.1‐diphenylethylene. If the synthesis is performed under the conditions when the elimination of “living” polystyrene chains from hexaadduct‐precursor is possible, heteroarm polymers have, on average, four arms of polystyrene and four arms of poly‐(2‐vinylpyridine). When the synthesis is performed under optimized conditions in nonpolar medium, star‐shaped molecules with total number of arms close to 12 were obtained.

The regioselectivity of fullerenols C60(OH)x determined by high-resolution solid-state13C and 1H NMR analysis

Abstract Fullerenols C60(OH)x with different number of OH-groups (3–12 per molecule) were obtained by using a specially developed two-step grafting procedure. The regioselectivity of bound to fullerene molecule hydroxyls was proved by solid-state 1H and 13C NMR. It has been found that the fullerenols with 2–3 OH groups per C60 contain some amount of non-converted residual t-Bu groups and the solo grafting of one hydroxyl to one bond occurs due to the structure of the intermediate product. Therefore, the fullerenols with a medium number of hydroxyls seem to be the most proper derivatives for further covalent conversions.

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.

Hydrodynamic, electrooptical, and conformational properties of fullerene-containing poly(2-vinylpyridines) in solutions

For C60 fullerene-containing poly(2-vinylpyridines) synthesized by anionic polymerization, the molecular mass and hydrodynamic size of macromolecules in solutions have been determined by molecular hydrodynamics (translational diffusion and viscometry) and electrooptics in dilute benzene and THF solutions. Under the same conditions in the molecular mass range (9.8–123) × 103, the hydrodynamic behavior of linear poly(2-vinylpyridines) and their molecular-mass dependences have been examined and the conformational characteristics of macromolecules have been established. The branching of macromolecules has been characterized by comparing the properties of star-shaped fullerene-containing and linear poly(2-vinylpyridines). With consideration of the hydrodynamic data interpreted within the framework of regular star model, it is inferred that on average three to four linear polymer chains with a molecular mass of (8 ± 3) × 103 for each chain are attached to a fullerene core of C60 in molecules of fullerene-containing poly(2-vinylpyridines). The specific Kerr constant of fullerene-containing poly(2-vinylpyridines) in dilute benzene solution is −(14 ± 1) × 10−12 cm5/[g (300 V)2]. As evidenced by the electrooptical data, the incorporation of fullerene into the polymer weakens self-association of macromolecules in solution.

Thermal desorption of covalently bound fullerene C60 from poly-N-vinylpyrrolidone films

Kinetics of formation of thermolysis products in heating of thin films of poly-N-vinylpyrrolidone and of poly-N-vinylpyrrolidone with covalently bound fullerene C60 was studied by thermal desorption mass spectrometry.