PA was doped by organolithium compounds in polar and non polar medium. A large range of doping rate is observed. The max. conductivity is correlated to the redox potential of dopants. New data on the influence of cation solvation are reported.

‘Model’ polymer stars with a fullerene core and arms of defined molar masses and low polydispersities can be prepared by grafting ‘living’ anionic polymers or macro-radicals onto C60. The specific chemical reactivity of C60 leads in both cases to a peculiar addition mechanism that allows to perfectly control the number of arms between 2 and 6. Upon addition of ‘living’ polymers, the carbanions generated on C60 are delocalized on a single conjugated molecule, and the observed upper limit of six grafts results from this specific situation. It is also possible to take advantage of the increase of reactivity of the carbanionic sites located on the fullerene with their number to produce more sophisticated architectures such as ‘palm-trees’ or ‘dumbbells’. Upon heating (PS)xC60 in solution the arms are released showing that the covalent bond between the fullerene and the polymer chains breaks first. The presence of this ‘weak’ bond is responsible for the decreased thermal stability of these compounds as compared to polystyrene. The reduced stability of any direct bond to C60 seems general as the addition onto C60 of only even number of macro-radicals generated through an atom transfer reaction results also from the lower stability of C60–Br as compared to PS–Br. The presence of grafted polymer chains on the C60 allows organizing this fullerene at the nanoscale in a polymer matrix using the well known self-assembling of block copolymers. To cite this article: C. Mathis et al., C. R. Chimie 9 (2006).

Various "living" polymers were grafted onto C-60. The number of arms of the so obtained "star" molecules can be controlled by stoechiometry and/or by varying the reactivity of the carbanion on the "living" chain against a double bond on the C-60. Even the oxanion of "living" polyethylenoxide is able to add onto the reactive double bonds on C-60. In Some conditions, the carbanions present on these alkaline salts of grafted fullerenes becomes able to initiate anionic polymerization of vinyl monomers. Using "living" poly(phenylvinylsulfoxide) as a precursor polymer for PA, polyacetylene chains could be attached to the fullerene.

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 (PSxC60) 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 PSxC60 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.

Hexa(phenyl)benzene (HPB) and hexakis(p-bromophenyl)benzene (HPB-Br) were submitted to controlled pyrolysis under mild conditions to prepare carbonaceous materials for Li-ion storage. Experiments were performed in evacuated sealed ampoules and different temperatures (in the range 500–600°C) and heating times (1 upto 5 days) were applied. Pyrolytic products were obtained as black flakes and characterised by elemental analysis, thermogravimetric analysis, UV–vis–NIR and Raman spectroscopies. Scanning electron microscopy exhibited several structures (nanorods, bundles, microspheres) on the surface of the flakes, depending on the precursor and on the pyrolysis procedure. Preliminary electrochemical measurements revealed lithium storage capacities upto 500mAhg−1.

Upon blending (PS)(6)C-60 with polyisoprene-b-polystyrene block-copolymers (PI-b-PS), well-defined microstructures such as lamellae or cylinders with a 10-100 nm periodicity are formed over large domains (tens of mu m) as a result of the self-organization of PI-b-PS in the solid state. Due to their incompatibility in polyisoprene, the stars are incorporated exclusively into the polystyrene lamellae (or cylinders) of the ordered microstructures, leading to the formation of periodic arrays of fullerenes.

The structure of ternary compounds involving alkali, tetrahydrofuran (THF) and single-walled carbon nanotubes have been investigated using neutron diffraction (ND). Hydrogen-deuterium substitution in THF, as well as the study of different alkali-based compounds, allow a layered structure around the nanotubes to be determined. ND results indicate that the alkali cations form a monolayer surrounding each tube of the bundle, while THF molecules intercalate between the decorated tubes and at the surface of the bundles. In spite of this insertion, the triangular bundle structure is preserved, albeit with a much larger lattice parameter, which depends on the size of the inserted cation.

Asymmetric and mikto-arm stars were synthesized by the stepwise addition of macro-radicals or of anionic polymer chains onto C60. Pure di-adducts (PSa)2C60 were obtained by atom transfer radical addition of a Br-terminated polystyrene (PSaBr). Tetra-adducts (PSa)2C60(PSb)2 and (PSa)2C60(PI)2 were prepared by grafting, respectively, two additional PSbBr or PIBr onto (PSa)2C60. The addition of ‘living’ polystyryllithium onto C60 can be stoichiometrically controlled. For example, the reaction of four PSaLi with one C60 led to the formation of (PSa)4C604−(Li+)4. The additional grafting of polystyryllithium (PSbLi) or polyisoprenyllithium (PILi) provided, respectively, (PSa)4C60(PSb)2 and (PSa)4C60(PI)2. All the stars were characterized using multiple detectors size exclusion chromatography (SEC).

The search for materials aimed at energy storage has prompted the synthesis of new materials which were obtained by pyrolysis of aromatic precursors under controlled conditions for the production of carbon based structurally disordered networks aimed at hydrogen or lithium storage. Obviously these materials consist of fully insoluble mixtures of different molecular species which escape the traditional physico-chemical techniques for structure determination. With the purpose of overcoming this difficulty we have developed and report here a systematic vibrational spectroscopic work which lays the basic concepts to be considered in the structural understanding of the molecules studied and can be extended to similar classes of complex carbonaceous materials.The (partial) structure of these systems and some of the reaction pathways at the molecular level can be inferred from the spectroscopic signals presented and discussed to be taken as key features for structural analysis. (c) 2005 Elsevier Ltd. All rights reserved.

A low-temperature pyrolytic stepwise method is proposed to produce substantial amount of a carbonaceous material, characterized by a graphenic structure. The pyrolyzed material has been submitted to ballmilling steps of different times, and the samples obtained were studied from their structural and electrochemical points of view. The crystallographic data have evidenced crystallites with a crystal domain size less than one nanometer and the grinding influence is discussed. Electrochemical experiments have been carried out in order to study the mechanism of the Li insertion/deinsertion process in the host material. Interesting values of Li specific capacity have been calculated from cycle experiments in Li coin cells at constant current and a test in a Li-ion laboratory-type cell is proposed. (c) 2005 The Electrochemical Society.

The thermal stability of well-defined hexa-adducts (PS)(6)C-60 in solution at temperatures around 100degreesC has been studied by multi-detector Size Exclusion Chromatography. The degradation reaction corresponds to a quantitative release of the polystyrene arms from the fullerene core through thermal cleavage of the PS-C-60 link. From the kinetics of formation of cut arms and the progressive decrease of the stars' functionality, we could establish that the reaction follows a stepwise "breaking" mechanism where a 6-arm star is first converted to a 5-arm star, then to a 4-arm star, and so on down to the ungrafted arm. Furthermore, not only does the thermal stability of the PS-C-60 bond increase if the functionality of the star decreases, but the difference is large enough to allow determination of the kinetics constants for the first three steps. The activation energy for the breaking of an arm-C-60 link is about 65 kJ/mol. The stability of (PS),C-60 slightly decreases with an increase of the arm length. MALDI-TOF mass spectroscopy has shown that both C-C bonds in alpha and beta positions to C-60 can be cut, but the breaking of the direct fullerene-arm bond is favored. We have also found that a polyisoprene-C-60 bond is about seven times less stable than a PS-fullerene link upon heating. (C) 2004 Wiley Periodicals, Inc.

Pure di- and tetra-adducts can be obtained by grafting polystyrene (PS) chains onto C-60 via an atom transfer radical addition. Stars with a C-60 Core and exactly six PS arms of molar mass ranging from 1000 to several 100,000 are easily produced by adding an excess of PSLi to the fullerene Tri- to penta-adductS can he prepared by controlling the stoichiometry PSLi/C-60. The number of grafts on the fullerene can be extended to seven or eight by initiation of the anionic polymerization of an adequate monomer with a "living" hexa-adduct or by grafting onto this latter an halogen terminated polymer.

This study illustrates the principle of a novel route to organize C-60 on the nanoscale. The method we propose uses the self-assembled structure of a host polystyrene-b-polyisoprene (PS-b-PI) copolymer as a scaffold to organize polystyrene stars with a C-60 core, C-60(PS)(f) (f = 2, 4, and 6). The effect of the molecular architecture of the stars (size of the PS arms and functionality f) on the microstructures formed in the blends with a symmetric PS-b-PI copolymer (30k/30k) has been investigated by transmission electron microscopy, differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS). The molar mass M-w* and the functionality f of the stars are two key parameters that control their solubilization in the host copolymer matrix, hence, the microstructures and the C-60 organization in the blends. Different regimes of solubilization have been identified as a function of the ratio M-w*/M-w(PS) between the molar mass of the stars and the PS block of the copolymer M-w(PS). Homogeneous and localized solubilization regimes are evidenced for C-60(PS)(6) stars with M-w*/M-w(PS) less than or equal to 0.35 and 0.6 less than or equal to M-w*/M-w(PS) less than or equal to 2, respectively. In the latter regime, the C-60 cores are preferentially anchored in the middle of the PS lamellae. We also demonstrated that the star's functionality f, i.e., its compactness, controls the maximum molar mass of the stars at the solubilization limit in the blends: the higher the functionality of the stars, the higher the molar mass of stars that can be solubilized in the PS lamellae of a copolymer. The overall results are illustrated through different phase diagrams that visualize the required conditions to achieve the spatial organization of C-60.

Br-terminated polystyrenes of controlled molar masses and low polydispersities prepared by atom transfer radical polymerization (ATRP) can be converted to macroradicals using an appropriate catalytic complex (CuBr/bipyridine/100 degreesC). The addition of this macroradicals PSdegrees to 6-6 bonds of C-60 follows a specific atom transfer radical addition mechanism that favors the grafting of even number of chains onto the fullerene core. This peculiar mechanism, resulting from the properties of C-60, offers an easy synthetic route toward well-defined di- and tetra-adducts. In these adducts the disturbance of the electronic structure of the fullerene is kept at its minimum, as only one double bond needs to be opened on the C-60 to add two PS chains and only two double bonds are converted to single bonds in the tetra-adduct. (C) 2004 Wiley Periodicals, Inc.

Pure hexa-adducts (PS)(6)C-60 can be prepared by addition of PS-Li onto fullerene C-60. These model polymer stars offer an opportunity to study the thermal stability of the bond between the fullerene and a grafted chain simply by SEC. At temperatures around 100 degreesC, the hexa-adduct is slowly converted into adducts of lower functionality and ungrafted chains. The experimental results are coherent with a step by step mechanism where the 6-arm stars are converted to 5-arm stars, then these latter to 4-arm stars and so on; the kinetics constant decreasing if the functionality of the stars decreases. The thermal stability decreases if the length of the grafts increases.

Polystyryl-lithium of low polydispersity has been reacted with C-60, C-70, C-84 and C-96 in a non-polar solvent. Star-shaped polymers were always obtained and in all cases the maximum number of grafts attached to the fullerene was found to be 6. This upper limit is a consequence of the fact that the number of pentagons stays constant whatever is the size of the fullerene. In order to get the needed reactive double bond, the pentagones have to form a pyracyclene unit (2 pentagons and 2 hexagons). The number of pentagons being always 12, no more than 6 chains can be grafted on a fullerene by this kind of chemistry.

The ultrafast nonlinear optical response of C60–polystyrene n-arm (n=3,6) star polymers in toluene solution is studied using the optical Kerr effect technique under excitation with 800 nm, 100 fs laser pulses. Their response is found to depend on the number and the molecular weight of the arms and to be much larger than that of pure C60. Finally, the second hyperpolarizability of the C60–polystyrene n-arm star polymers is determined.

Halogen terminated PS chains of low polydispersity, prepared by atom transfer radical polymerization (ATRP), can be converted to macro-radicals using an atom transfer reaction and so attached to C,,. Depending on the stoichiometry PS-Br/ C-60 2 or 4 chains are grafted onto the fullerene. We propose a mechanism which can explain that no adducts with an odd number of arms are formed.

Two methods to prepare controlled three dimensional structures including Cso molecules as knots are described. For the first network synthesis, THF soluble C602−(K+)2 is reacted with a “living” polystyrene bearing a carbanion at each end. The use of the fullerene dianion is necessary to avoid complications originating from electron transfer from the carbanions to C60. The second method, developed to increase the functionality of the knots, consists of reacting C60 with high functionality polystyrene stars where each branch bears at its end a carbanion. The properties of these networks based on cm, compare well with classical PS gels.

The photophysical properties of a new hexa-polystyrene adduct of C-60 were determined. This compound presented the characteristic features of a C-60 with multiple adducts in solution, i.e. a decrease of the triplet quantum yield and a blue shift of the triplet-triplet (T-T) absorption spectrum as compared to unlinked C-60. However the values of the quantum yield of singlet oxygen photosensitization and consequently of the triplet quantum yield were still relatively high, of the order of 0.65, This favorable triplet quantum yield, the high content of fullerene in (PS1400)(6)C-60, and the isotropic 3D structure apt to prevent close contact between fullerene cages might confer on this new compound good optical limiting properties. (C) 1999 Elsevier Science B.V. All rights reserved.