Synthesis of Buckminsterfullerene C60 functionalised core cross-linked star polymers

Buckminsterfullerene C₆₀ core functionalised core cross-linked star (CCS) polymers have been prepared for the first time, using atom transfer radical polymerisation and the arms-first approach. A simple and efficient method is presented which allows the construction of star polymers consisting of a large number of arms and multiple units of C₆₀ per core, far in excess of that obtained previously. The C₆₀ CCS polymers were characterised by gel permeation chromatography (GPC), UV-vis spectroscopy and cyclic voltammetry (CV). GPC revealed that the C₆₀ CCS polymers possess weight average molecular weights (M_w) ranging from 172-411 kDa and up to 30 arms per macromolecule. The average number of molecules of C₆₀ per CCS polymer core was found to be dependent on the C₆₀/PMMA ratio employed and was determined by UV-vis spectroscopy to range up to 6.2. CV revealed that, like pristine C₆₀, the C₆₀ CCS polymers possessed three reversible one electron reductions. However, the reduction potentials were positively shifted, implying that the electron affinity of these macromolecules is higher than pristine C₆₀.     

High rate performance of highly dispersed C60 on activated carbon capacitor

Fullerene-activated carbon composite electrodes were prepared and their charge/discharge characteristics were studied for use in a high power electric double-layer capacitor. The capacitance of the C₆₀-loaded activated carbon fiber (ACF) electrodes became greater than that of the unloaded ACF at charge/discharge current densities above 50 mA/cm². In order to obtain a highly dispersed C₆₀-loaded electrode, an ultrasonic treatment was performed. The size of the C₆₀ agglomerate decreased from 1-2 to 0.1 μm or less, and the capacitance of the C₆₀-loaded ACF electrodes increased with an increase in the ultrasonic treatment time. A higher capacitance of 172 F/g was obtained at 50 mA/cm² on a 1 wt% C₆₀-loaded electrode with ultrasonic treatment, and the C₆₀-loaded ACF electrode also showed a higher cycle performance.     

Self-assembly of C60 containing poly(methyl methacrylate) in ethyl acetate/decalin mixtures solvent

[60]Fullerene (C₆₀) was mono-substituted with well-defined poly(methyl methacrylate) (PMMA-b-C₆₀) using the atom transfer radical polymerization (ATRP) technique. The self-assembly behaviors of PMMA-b-C₆₀ in ethyl acetate (EA) and decalin mixtures were studied using laser light scattering (LLS) and transmission electron microscopy (TEM). Homogeneous solutions of PMMA-b-C₆₀ can be obtained in the solvent mixtures containing more than 40 wt% EA, where the molar ratio of decalin to EA is close to 1. For each solvent mixture, unimers coexist with micelles and large aggregates. The sizes of PMMA-b-C₆₀ micelles and aggregates are independent of polymer concentration, confirming that they are produced via the closed association mechanism. For the various solvent mixtures, the weight-averaged molecular weights, M_w of the PMMA-b-C₆₀ aggregates range from 4.1×10⁷ to 12.5×10⁷ g/mol. The hydrodynamic radii of the large aggregate, R_h, vary from 90 to 136 nm, while the z-averaged radii of gyration, R_g, range from 210 to 311 nm. The R_g/R_h value for each solvent mixture is ∼2.3, which is independent of decalin contents in the mixed solvents. The morphological study using the transmission electron microscope suggests that the large aggregates are composed of porous large compound micelles (LCM) in solution.     

Synthesis of alkali-metal-doped C60 nanotubes

C₆₀ nanotubes have been synthesized by a solution-solution method. After degassing in a dynamic vacuum, the C₆₀ nanotubes doped with alkali metals by means of vapor evaporation method. Different temperatures have been studied to evaporate the alkali metals for the doping experiments. Raman spectrum was further employed to analyze the doping concentration of the obtained samples. It was found that all three alkali metals (Li, Na and K) used can be efficiently doped into the C₆₀ nanotubes, forming A_xC₆₀ nanotubes. The doping concentration of Li, Na changed from low to high level, depending on the experiment temperatures, while K doping always gave saturated doping. The melt points, the ionic sizes and vapor pressures of alkali metals were thought to affect the final doping results.     

Deposition of C60, C70 and C84 fullerene molecules, in benzene via a change of the fluid state, from a gas–liquid two phase region to the critical point

We dissolve C₆₀, C₇₀ or C₈₄ molecules in benzene and change the fluid state from a gas–liquid two-phase region (25.0 °C) to the critical point (289.0 °C) and from the critical point to the original state (25.0 °C) along the gas–liquid coexistence curve. We find that particle-like and whisker-like nano/micro clusters, which are composed of C₆₀ molecules, deposit on the surface of a silicon substrate placed vertically in C₆₀/benzene solution during the temperature change, whereas no appreciable clusters are detected on the silicon substrate in either C₇₀/benzene or C₈₄/benzene solutions. The clusters, in which fcc lattice structures are formed by C₆₀ molecules, remain stable in the solution. The present result suggests that C₆₀ molecules can be separated and extracted from a mixture of C₆₀, C₇₀ and C₈₄ molecules dissolved in benzene.     

Synthesis and solid-state studies of self-assembled C60 microtubes

C₆₀ microtubes were fabricated by a modified solution evaporation method, evaporating a solution of C₆₀ in toluene in an atmosphere of m-xylene at room temperature. The C₆₀ microtubes have outer diameters ranging from 2 to 8 μm. IR spectra, TG analysis and X-ray diffraction showed a solvated structure for the as-grown C₆₀ microtubes. Through a gentle heat-treatment in vacuum, pure C₆₀ microtubes with single crystalline fcc structure were obtained after the elimination of solvents. It is suggested that the C₆₀ microtubes form through self-assembly from several individual C₆₀ nanorods.     

The intercalation of C60-containing PEO into layered MnPS3

This paper reports the synthesis and magnetism of a new polymer-inorganic intercalation nanocomposite based on a C₆₀-containing poly(ethylene oxide) (C₆₀-PEO) into layered MnPS₃, which is characterized by XRD, IR and thermal analyses. The lattice expansion (Δd) of the intercalation nanocomposite is about 9.3 Å indicating the successful intercalation. And the charge balance is maintained by K⁺ ions coordinating with PEO chain of C₆₀-PEO polymer, which come from the pre-intercalation compound Mn_1−xPS₃[K_2x(H₂O)_y]. Magnetic measurements indicate that the intercalation nanocomposite (C₆₀-PEO/MnPS₃) exhibits a magnetic phase transition from paramagnetism to ferrimagnetism at about 40 K. And the distinctive hysteresis of M-H relationship further confirms that it is a low temperature ferrimagnetic nanocomposite.     

Electrochemical properties of two-component polymers of palladium and pyrrolidine and piperazine derivatives of C60

Redox-active films have been generated via electrochemical reduction in a solution containing palladium(II) acetate and [C₆₀]fullerene, or derivatives of C₆₀. The C₆₀ derivatives include piperazine (piperazine-C₆₀), pyrrolidine (CH₃-pyr-C₆₀), and a pyrrolidine salt, [(CH₃)₂-pyr-C₆₀]⁺ attached to the fullerene unit. In these films, fullerene moieties are covalently bonded to palladium atoms to form a polymeric network. The polymer yields involving the piperazine and pyrrolidine derivatives of C₆₀ are significantly lower than the yield of the C₆₀/Pd film. The CH₃-pyr-C₆₀/Pd and [(CH₃)₂-pyr-C₆₀]⁺/Pd films are electrochemically active in the negative potential region due to the reduction of the fullerene moiety. Reduction of the CH₃-pyr-C₆₀/Pd film is accompanied by the transport of supporting electrolyte cations from the solution into the film. In the first reduction step of the [(CH₃)₂-pyr-C₆₀]⁺/Pd film, both cations and anions of the supporting electrolyte are involved. The piperazine-C₆₀/Pd film exhibits electrochemical activity at both negative and positive potentials. In the negative potential region, reduction of the fullerene cage takes place. Oxidation of the piperazine moiety is responsible for the observed current in the positive potential range. Here, the oxidation process of this polymer is significantly influenced by the presence of metallic palladium particles in the film.     

Solvated structure of C60 nanowhiskers

This work characterizes the structure of C₆₀ nanowhiskers prepared by the liquid-liquid interfacial precipitation method in the C₆₀-saturated m-xylene and isopropyl alcohol system. Transmission electron microscopy and X-ray diffraction measurement show that the C₆₀ nanowhiskers had a hexagonal structure with cell dimensions a = 2.407 nm and c = 1.018 nm which is different from pristine C₆₀. The structure of the C₆₀ nanowhiskers in solution is different from that of the solvated structure reported for the C₆₀ nanotubes but similar to that reported for the C₆₀ bulk crystal solvated with m-xylene. X-ray diffraction analysis also showed a shift to fcc structure after solvent evaporation. The C₆₀ nanowhiskers prepared using toluene as solvent also showed a similar solvated structure, and a more rapid structural change into fcc upon drying was again observed.     

Self-assembly of thermo-responsive poly(oligo(ethylene glycol) methyl ether methacrylate)-C60 in water-methanol mixtures

Well-defined statistical copolymer of poly (di(ethylene glycol) methyl ether methacrylate-stat-oligo(ethylene glycol) methyl ether methacrylate-C₆₀ ((PMEO₂MA-stat-POEGMA₃₀₀)-C₆₀) was synthesized via atom transfer radical polymerization (ATRP) reaction and atom transfer radical addition (ATRA) processes. The lower critical solution temperature (LCST) of PMEO₂MA-stat-POEGMA₃₀₀ increased from 42 to 95 °C when the amounts of methanol was increased from 0 to 30 vol%, beyond which the LCST could not be quantified. Similarly, the LCST of (PMEO₂MA-stat-POEGMA₃₀₀)-C₆₀ also increased with methanol content, however it was lower than PMEO₂MA-stat-POEGMA₃₀₀ for all methanol/water compositions. The CMC of (PMEO₂MA-stat-POEGMA₃₀₀)-C₆₀ increased with increasing methanol content, suggesting that methanol is a better solvent for PMEO₂MA-stat-POEGMA₃₀₀ segment. The amphiphilic (PMEO₂MA-stat-POEGMA₃₀₀)-C₆₀ structure formed spherical micelles in water/methanol mixture, and larger micelles were formed at higher methanol content. The hydrodynamic radius (R_h) remained constant at temperature below the LCST. It increased dramatically at temperature greater than the LCST, and the (R_g/R_h) increased from ∼0.75 to ∼1.0. We believe that the (PMEO₂MA-stat-POEGMA₃₀₀) coronas dehydrate at higher temperature, and the micelles associate to form larger aggregates. In water/methanol mixtures, core-shell micelles and large compound micelles are produced below and above the LCST respectively.     

Supramolecular assembled C60-containing carboxylated poly(dimethylsiloxane) composites

Supramolecular assembled nanocomposites were prepared through the solution casting of the complexing mixtures from the side chain carboxylated poly(dimethylsiloxane) (PDMS) with the 1-(4-methyl)-piperazinylfullerene (MPF). FT-IR and XPS analyses reveal that there are strong ionic interactions between the two components. Small-angle X-ray scattering study shows the formation of MPF fullerene nanodomains dispersed in the PDMS matrix, but no highly ordered structures, which is confirmed with TEM images. Compared to its polymeric precursor, the MPF crosslinked composites exhibit superior thermal mechanical stability and dramatic increase in the storage and loss moduli. Moreover, elastic response exceeds viscous response in the composites due to the formation of crosslinking structures. The increase of the MPF content in the composites leads to a denser packing of MPF nanodomains, resulting in better thermal, mechanical, and viscoelastic properties. The decrease in the carboxylic acid groups along the PDMS chains reduces the crosslinking density of the PDMS/MPF composites. The composites show a combined dielectric property from both PDMS and MPF components.     

Enantioanalysis of S-deprenyl using enantioselective, potentiometric membrane electrodes based on C60 derivatives

Enantioselective, potentiometric membrane electrodes based on (1,2-methanofullerene C₆₀)-61-carboxylic acid, diethyl (1,2-methanofullerene C₆₀)-61-61-dicarboxylate and tert-butyl (1,2-methanofullerene C₆₀)-61-carboxylic acid were proposed for the enantioanalysis of S-deprenyl in pharmaceutical compounds. Molecular modeling calculations were performed to prove the reliability of the proposed electrodes. The different characteristics involved in this analysis were explained, namely (i) the stability of each molecule using total energy, hardness and dipole moment, and (ii) the explanation of the mechanism of interaction using intermolecular forces (moderate hydrogen bond interactions), atomic charges and electrostatic potential. Electronic structures as well as molecular interaction have been investigated using Hartree-Fock theory, 3-21G(*) basis set. Stability and feasibility of all the generated structures were supported by their respective energy minima and fundamental frequencies.     

Grafting of poly(ethylene oxide) onto C60 fullerene using macroazo initiators

In order to improve the solubility of C₆₀ fullerene in conventional solvents, grafting of hydrophilic poly(ethylene oxide) (PEO) by utilizing the radical-trapping nature of C₆₀ fullerene was investigated. Macroazo initiators containing a poly(ethylene oxide) unit, known as Azo-PEO, were prepared at various molecular weights by the reaction of 4,4′-azobis(4-cyanopentanoyl chloride) with poly(ethylene glycol) methyl ether. PEO radicals formed by thermal decomposition of Azo-PEO were successfully trapped by C₆₀ fullerene to give PEO-grafted C₆₀ fullerene. Their structures were confirmed by FT-IR spectroscopy, size exclusion chromatography, UV-vis spectroscopy, and differential scanning calorimetry. When Azo-PEO with low-molecular weight was reacted with C₆₀ fullerene, a bis-adduct, C₆₀-(PEO)₂, and a tetrakis-adduct, C₆₀-(PEO)₄, were formed. In contrast, in reactions with Azo-PEO of higher molecular weight, only the bis-adduct was formed, and no formation of the tetrakis-adduct was observed. The structure of bis-adduct was found to be 1,4-type. The solubility of C₆₀ fullerene in water, THF, methanol, and other conventional organic solvents was remarkably improved by grafting of PEO. In addition, the thermal stability of PEO was dramatically increased by grafting onto C₆₀ fullerene.     

Synthesis of C60 Fullerene-Silica Hybrid Nano Structures

We have recently demonstrated a procedure for the synthesis of silica nanometer and micrometer particles under modest conditions. Here we report the synthesis of C₆₀ fullerene-silica hybrid nanometer sized materials via sol-gel processing at neutral pH and under ambient conditions. The C₆₀ fullerene, when functionalized, was water-soluble and also able to facilitate the formation of silica structures from an aqueous silica precursor. This C₆₀ fullerene had similar functionality to the cationically charged polymers, which have been reported earlier to act as catalysts/templates for silicification. The resulting organic-inorganic hybrid was studied using SEM, EDS and UV/Vis spectroscopy. These hybrid materials may have applications in areas such as optical devices, semiconductors, chemical sensors, catalysis and in the medical field. The results presented in this study may be useful in developing a process for the synthesis of novel organic-inorganic nanometer sized materials and for the biomimetic synthesis of silica.     

Electrocatalytic oxidation of norepinephrine at a reduced C60-[dimethyl-(β-cyclodextrin)]2 and Nafion chemically modified electrode

The reduced C₆₀-[dimethyl-(β-cyclodextrin)]₂/Nafion chemically modified electrode is demonstrated to catalyze the electrochemical response of norepinephrine (NE) by cyclic voltammetry. A pair of well-defined redox waves were obtained and the calculated standard rate constant (k_s) is 4.4×10⁻³ cm s⁻¹ at this reduced CME, indicating that the reduced C₆₀-[dimethyl-(β-cyclodextrin)]₂ can act as promoter to the electron transfer of NE.     

Synthesis and photophysical properties of a charm-bracelet type C60-grafted PPV derivative

Synthesis and photophysical properties of a new soluble C₆₀-grafted PPV polymer have been described. Fluorescence quenching of the PPV moiety in C₆₀-grafted PPV polymer was observed, suggesting the energy- and/or electron transfer within the polymer. The fluorescence decay profiles at around 500 nm of this polymer both in chloroform and benzonitrile display a single exponential decay giving the fluorescence lifetimes of 1.10-1.27 ns, which are slightly shorter than that of PPV (about 1.50 ns). The nanosecond transient absorption band of C₆₀-grafted PPV polymer was observed at 740 nm corresponded to the excited triplet state of C₆₀, which decreased in benzonitrile, indicating the existence of the extra decay path of the singlet excited state of the C₆₀ other than intersystem crossing. Upon heating this polymer exhibits typical semilunar liquid crystalline texture, being closely associated with its polymeric structure with long solubilizing alkoxy side chains.     

Photoelectric catalytic degradation of methylene blue by C60-modified TiO2 nanotube array

Fullerene (C₆₀)-modified TiO₂ nanotube array (TNA) was prepared by the electrophoresis deposition technique. The as-prepared samples showed the high efficiency for the photoelectric catalytic (PEC) degradation of nonbiodegradable azodyes methylene blue (MB). The highest PEC activity of C₆₀-modified TNA (TNA/C₆₀) was achieved at a lower bias potential (4.0 V), which was 2.3 times of the highest activity of TNA at 5.0 V. The high PEC activity came from the synergetic effect between C₆₀ and TiO₂, which promoted the charge separation, influenced the charge distribution of the electrical double layer and reduced the impedances of the Helemholtz and depletion layers. Moreover, the oxidation of MB was a quick process during the PEC degradation, and the process began with the oxidation of the dimethylamino group, which was different from the photocatalytic (PC) process began with the oxidation of S atom; MB was mineralized completely during PEC degradation.     

Thermal degradation in bulk and thin films of 2-, 4-, and 6-arm polystyrene stars with a C60 core

The thermal stability (TS) of hexa-, tetra-, and di-arm polystyrene (PS) stars with a C₆₀ core was studied by thermal gravimetric analysis and mass-spectrometry. The quantitative production of volatile products, their composition and their formation kinetics during heating of (PS_xC₆₀) are reported. A bimodal release of styrene is observed. The first release takes place about 100 °C before the depolymerization temperature of styrene and all the C₆₀ comes out at this lower temperature. That results from a complete breaking of the weak PS-C₆₀ bonds followed by a partial depolymerization of the PS arms initiated by the so formed radicals. The amount of PS ‘surviving’ this first depolymerization step increases with the length of the arms and its TS is close to that of pure PS. The thermal stability of the PS_xC₆₀ stars decreases if the number of arms increases and, from the activation energy of the release of styrene and C₆₀, it was possible to estimate the PS-C₆₀ bond strength for these three adducts.     

Electrochemical quartz crystal microbalance studies of thin-solid films of higher fullerenes: C76, C78 and C84

Thin-solid films of higher fullerenes, viz. C₇₆, C₇₈ and C₈₄, were prepared by the drop coating technique and characterized by simultaneous cyclic voltammetry and piezoelectric microgravimetry with the use of an electrochemical quartz crystal microbalance. Properties of the films were compared with those reported earlier for the C₆₀ and C₇₀ thin-solid films. The effect of nature of the counter cation on electrochemical properties of the films has been probed by employing acetonitrile solutions of two different 0.1 M supporting electrolytes, namely tetra(n-butyl)ammonium (TBA⁺) hexafluorophosphate and potassium hexafluorophosphate. Stability of the films with respect to dissolution depends on the fullerene oxidation state as well as on the nature of both the fullerene in the film and the counter cation in the supporting electrolyte. The TBA⁺ counter cation ingress to the film for compensation of the negative charge of the reduced fullerene is accompanied by the acetonitrile solvent intake. The number of acetonitrile molecules per TBA⁺ counter cation entering the film is higher the higher the fullerene. Also, the Langmuir films of higher fullerenes were prepared at the air-water interface and the film morphology was characterized by the Brewster angle microscopy.     

Enhanced electrochemical response of carbamazepine at a nano-structured sensing film of fullerene-C60 and its analytical applications

In the present work, electrochemical behavior of carbamazepine (CBZ) at fullerene-C₆₀ modified glassy carbon electrode has been investigated. Cyclic voltammogram of CBZ showed two each of oxidation and reduction peaks at fullerene-C₆₀ modified glassy carbon electrode (GCE) in phosphate buffer of pH 7.2 at the scan rate of 100 mV s⁻¹. The fullerene film on GCE surface exhibited excellent enhancement effects on electrochemical response of CBZ. Marked negative shift in peak potential with enhanced peak current was noticed in the cyclic and differential pulse voltammograms of CBZ at fullerene-C₆₀ modified electrode. The effect of accumulation time, amount of fullerene-C₆₀ and pH on electrochemical behavior of CBZ has been investigated using differential pulse voltammetry (DPV). An analytical method was developed for the determination of CBZ employing DPV. The oxidation peak current of CBZ was observed to be linearly dependent on the concentration of CBZ in the range of 90 nM–10 μM. The values of limit of detection and limit of quantification were found to be 16.2 nM and 54.0 nM, respectively. The developed DPV method was satisfactorily applied to the determination of CBZ in pharmaceutical formulations, spiked human serum and urine samples.