Self-assembled micelles of well-defined pentaerythritol-centered amphiphilic A4B8 star-block copolymers based on PCL and PEG for hydrophobic drug delivery

Biodegradable star-shaped poly(?-caprolactone) (PCL) with four arms were synthesized by ring-opening polymerization (ROP) from a symmetric pentaerythritol core via the ‘‘core-first’’ strategy. Subsequently, two samples of the amphiphilic A₄B₈ star-block copolymers with symmetrical topologies [4s(PCL-b-2sPEG)] were synthesized by a macromolecular coupling reaction between carboxyl-terminated poly(ethylene glycol) (PEG) and 4-arm star-shaped PCL macromers with eight -OH end groups. The latter was prepared by attaching 3-hydroxy-2-(hydroxymethyl)-2-methylpropanoic acid (HHMPA) to 4sPCL using a simple two-step reaction sequence. The in vitro cytotoxicity test indicated no apparent cytotoxicity. The amphiphilic star-block copolymers are capable of self-assembling into spherical micelles in water at room temperature, and they possess low critical micelle concentrations (CMCs) of 2∼8 mg/L in aqueous solution which was determined by fluorescence spectroscopy using pyrene as a probe. Transmission electron microscopy (TEM) measurement demonstrated that the micelles exhibit a spherical shape with a size range of 30∼50 nm in diameter. In addition, the hydrophobic and anticancer drug, quercetin, is loaded effectively in the polymeric micelles, suggesting that these new materials are appropriate candidates as hydrophobic drug nanocarriers.     

Synthesis of biodegradable pentaarmed star-block copolymers via an asymmetric BIS-TRIS core by combination of ROP and RAFT: From star architectures to double responsive micelles

Biodegradable star-shaped poly(?-caprolactone) and poly(?-caprolactone-b-l-lactide) (5sPCL-b-PLLA) with five arms were synthesized by ring-opening polymerization (ROP) from an asymmetric BIS-TRIS core via “core-first” strategy. Subsequently, a series of amphiphilic and double responsive star-block copolymers were synthesized by Z-RAFT star polymerization of N,N-dimethylamino-2-ethyl methacrylate (DMAEMA) from the star-shaped macro-RAFT agent, which was prepared by attaching 3-benzylsulfanylthiocarbonylthiocarbonylsufanylpropionic acid (BSPA) to 5sPCL-b-PLLA using a simple two-step reaction sequence. GPC and ¹H NMR data demonstrated the polymerization courses are under control. The molecular weight of 5sPCL-b-PLLA-b-DMAEMA increased with the monomer conversion, and the molecular weight distribution was in the range of 1.19-1.37. The spherical micelles with degradable core and pH/thermo-double sensitive shell had been prepared from the aqueous medium of the amphiphilic star-shaped copolymers by dialysis method. Both pH and thermal-responsive behaviours of copolymer micelles obtained in this study were investigated. The micelle size and morphology were measured by DLS, AFM and TEM.     

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.     

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.     

Preparation and spectroscopic properties of chlorofullerenes C60Cl24, C60Cl28, and C60Cl30

We report easy preparation of recently discovered highly chlorinated fullerenes T_h-C₆₀Cl₂₄, C₁-C₆₀Cl₂₈, and D_3d-C₆₀Cl₃₀ in high-temperature reactions of C₆₀ with PCl₅ and ICl. Formation and interconversion of chlorofullerenes was investigated in details for C₆₀-ICl system. C₆₀Cl₂₈ is the least stable chlorofullerene that undergoes rearrangement (accompanied by partial chlorine elimination) into more stable T_h-C₆₀Cl₂₄ under more drastic reaction conditions (increased temperature and time of chlorination). T_h-C₆₀Cl₂₄ yields D_3d-C₆₀Cl₃₀ at temperatures above 220 °C via a sequence of rearrangements and further addition of chlorine. In contrast to the fullerene reaction with ICl, interaction of C₆₀ with PCl₅ is very selective with respect to formation of C₆₀Cl₂₄ in a wide temperature range. Solid-state electronic (UV-Vis) and vibrational (IR) spectra of chlorinated fullerenes C₆₀Cl₂₄, C₆₀Cl₂₈, C₆₀Cl₃₀ and fluorinated fullerenes C₆₀F₁₈ and C₆₀F₃₆ were recorded in the spectral range between 30 and 45,000 cm⁻¹. Raman spectra were also acquired for all investigated compounds. Moreover, molecular geometry of the C₆₀Cl₂₄ and its theoretical IR-absorption spectrum were calculated using B3LYP/STO-3G chemistry model.     

Electrochemical behavior of C60 films and C60/lipid films in ionic liquids

Cyclic voltammograms (CVs) of C₆₀ films and C₆₀ embedded in cast films of triple-tailed cationic surfactant solutions and salt-free zero-charged cationic/anionic (catanionic) surfactant vesicles on glassy carbon electrode in a typical room-temperature ionic liquid (RT-IL), 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]), were examined. CVs show typically electrochemical oxidation and reduction. The salt-free zero-charged catanionic surfactant bilayer vesicles were determined by freeze-fracture transmission electron microscopy (FF-TEM) images and small-angle X-ray scattering (SAXS) measurements. The cast films of the salt-free zero-charged catanionic surfactant vesicles incorporated C₆₀ molecules were employed to study the electrochemical properties in RT-ILs, which would open new fields for the bulk electronic properties of fullerenes or their derivatives in ionic liquids.     

Synthesis of a hexagonal modification of C60 using cryoextraction

Samples of the hexagonal close-packed phase (h.c.p.) of fullerite C₆₀ with a low (less then 7%) content of more stable face-centered cubic (f.c.c.) phase were synthesized using cryoextraction with n-hexane. X-Ray diffraction analysis and thermogravimetry were applied for characterization of the samples. The role of n-hexane in the formation of the h.c.p. structure is discussed.     

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 reduction of 1,2-diiodoethane by anions of supramolecular complex of (β-CD)2/C60 in DMF solution

The homogeneous electrocatalytic reduction of 1,2-diiodoethane by anions of the supramolecular complex of (β-CD)₂/C₆₀ in DMF solution is reported. The results show that the trianion of (β-CD)₂/C₆₀ exhibits electrocatalytic behavior towards the reduction of 1,2-diiodoethane, whereas the dianion is unable to reduce the diiodoethane. The second-order catalytic rate constant in DMF solution was determined to be 3.1 × 10⁵ M⁻¹ s⁻¹ by analysis of voltammetric responses under pseudo-first-order conditions with respect to (β-CD)₂/C₆₀. The results suggest that the host β-cyclodextrin molecules have little effect on the electrocatalytic ability of the encapsulated C₆₀ toward organic halides.     

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.     

Synthesis and growth mechanism of differently shaped C60 nano/microcrystals produced by evaporation of various aromatic C60 solutions

We present a detailed study of the synthesis of C₆₀ nano- and microrods as well as crystals with normal shapes by the evaporation of C₆₀ solutions based on different aromatic solvents. C₆₀ nano- and microrods are grown with high yield by vaporizing C₆₀ solutions in meta-isomers of aromatic solvents on different substrates while para-isomers give a different type of growth leading to highly crystalline two- and three-dimensional nano- and microcrystals with fcc structure. The role of solvent properties was investigated by using positional isomers containing different halogen radicals. The as-grown crystal rods form hexagonal structures but transform into fcc structure on annealing in vacuum. IR and EDX analysis indicate that solvents remain in the hexagonal nano- and microrods, while it is hard to detect any trace of solvents in the two- or three-dimensional nano- and microcrystals. Furthermore, we present direct proof of the nucleation-growth mechanism for C₆₀ rods. By the vaporization method, the solubility of C₆₀ in the studied halogen aromatic solvents is found to correlate with the diameter distribution of the C₆₀ rods and we suggest that the chemical affinity of the aromatic solvent molecules to C₆₀ may determine its ability to force C₆₀ to form rod-shaped crystals.     

C60 fullerene inclusions in low-molecular-weight polystyrene-poly(dimethylsiloxane) diblock copolymers

We have synthesized low-molecular-weight diblock copolymers of polystyrene-block-poly(dimethylsiloxane) with total molecular weights <12 kg/mol and PS volume fractions of ∼0.2. We have investigated the phase behavior of the PS-PDMS in its pure state and with up to 10 wt% of C₆₀ added. The C₆₀ was shown to selectively segregate into the PS phase only although its solubility limit is ∼1 wt%. Although the C₆₀ aggregates above 1 wt%, the cylindrical morphology observed in the pure copolymer bulk samples persists in the C₆₀-copolymer composites even up to 10 wt% C₆₀ loading. In thin films, the pure copolymer possesses a highly ordered morphology with grains hundreds of microns across. When C₆₀ is blended with the copolymer the high degree of order rapidly decreases due to increasing numbers of defects observed.     

Soot-free synthesis of C60

A new synthetic medium for the production of C₆₀ has been found that does not produce soot. C₆₀ was produced in the liquid phase of an aerosol of precursor soot at 700 °C. The precursor soot aerosol, a high temperature stable form of hydrocarbon, was produced by pyrolysis of acetylene at atmospheric pressure in a flow tube reactor. At 700 °C, the effluent particles were found to contain PAHs, small hydrocarbons and fullerenes but no observable black material. However, when the reactor temperature was changed to 800 °C, soot was also produced in the effluent particles along with PAHs and other small hydrocarbons, and the fullerene product disappeared. These results show a clear competition between the production of fullerenes and other forms of carbon. The filter-collected effluent was shown to be completely soluble in conventional solvents suggesting the possibility of an efficient cyclic synthetic process. Fullerenes were only found in the particle phase implying the first observed liquid phase synthesis of C₆₀.     

Soot-free synthesis of C60

A new synthetic medium for the production of C₆₀ has been found that does not produce soot. C₆₀ was produced in the liquid phase of an aerosol of precursor soot at 700 °C. The precursor soot aerosol, a high temperature stable form of hydrocarbon, was produced by pyrolysis of acetylene at atmospheric pressure in a flow tube reactor. At 700 °C, the effluent particles were found to contain PAHs, small hydrocarbons and fullerenes but no observable black material. However, when the reactor temperature was changed to 800 °C, soot was also produced in the effluent particles along with PAHs and other small hydrocarbons, and the fullerene product disappeared. These results show a clear competition between the production of fullerenes and other forms of carbon. The filter-collected effluent was shown to be completely soluble in conventional solvents suggesting the possibility of an efficient cyclic synthetic process. Fullerenes were only found in the particle phase implying the first observed liquid phase synthesis of C₆₀.     

Functionalization of C60 with gold nanoparticles

Gold nanoparticles (GNPs) with attached C₆₀ molecules (C₆₀-GNPs) were prepared through the amination reaction of fullerene C₆₀ with peripheral amino groups located on the surface of gold. Molecules of 4-aminobenzenethiol/1-hexanethiol containing amino groups were introduced onto the surface of gold by the reduction of a gold salt (HAuCl₄) with sodium borohydride (NaBH₄) in a one-pot way, which was accompanied by anchoring of the targeted thiol mixture on the gold cluster by Au-S bonds. This simple system avoids many difficult reactions and purification processes and does not involve a complicated chemical modification of C₆₀ and exchange reactions of GNPs.     

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.     

Young’s modulus of crystalline C60 nanotubes studied by in situ transmission electron microscopy

Bending tests of crystalline nanotubes composed of fullerene C₆₀ molecules are performed inside a high-resolution transmission electron microscope. We fixed one side of a C₆₀ nanotube with a body-centered tetragonal structure with typical inner and outer diameters, i.e., 180 nm and 510 nm, respectively, and then applied concentrated forces on the other side using piezomanipulation of a silicon nanotip. The bending process was observed in situ by transmission electron microscopy with simultaneous measurements of the forces by an optical deflection method. It was found that the Young’s modulus of the nanotube was estimated to be 62–107 GPa, which was 1.1–3.3 times larger than that of C₆₀ nanowhiskers. The result concerning the increase in the Young’s modulus of the C₆₀ nanotube provided an experimental evidence for the structural model composed of an inner core and a surface shell for C₆₀ nanowhiskers.     

本体法St改性C5石油树脂的合成

用本体法在C5石油树脂上接枝单烯烃苯乙烯(St),考察了不同聚合条件对产物的影响。随着St含量的增加,C5石油树脂的软化温度先降后升,在w(St)为37.5%,引发剂质量分数为1.0%,反应温度为200℃,反应时间为2.0 h时,软化温度达到最小值71℃。黏度测试表明,St改性C5石油树脂具有较好的流动性。铁钴比色分析表明,随着引发剂用量的增加,St改性C5石油树脂的色度增大,在引发剂质量分数为1.0%时,该石油树脂的色度为2#。     

Molecular dynamics simulation of triaxial compression of C60 and C80 solids

Present work investigates the triaxial compression behavior of face-centered cubic C₆₀ and C₈₀ solids using molecular dynamics simulation. Second-generation empirical bond-order potential governs the atomic interactions within a C₆₀ or C₈₀ molecule, whereas van der Waals potential dominates the interactions between C₆₀ or C₈₀ molecules. The equilibrium lattice spacings for C₆₀ and C₈₀ solids are obtained as 14.26 Å and 15.56 Å, respectively. Investigation focuses on the effects of: (i) van der Waals potential, (ii) temperature and (iii) loading rate, on the bulk moduli and hydrostatic stress vs. volumetric strain curves of C₆₀ and C₈₀ solids. Our results showed that these properties are dependent on loading rate and the choice of van der Waals potential, but insensitive to temperature change.