Claude Mathis

Honeycomb membranes made from C60(PS)6

Abstract A set of six branched polystyrene stars with different molecular weights have been prepared by reaction of living polymer on C 60 . By evaporation of carbon disulflde solutions of these polymers in humid atmosphere, one obtains porous membranes with honeycomb pore organisation when the branch molecular weigth is in a range 3000–50 000.

Physico-chemical behavior in solution of star-shaped polystyrene with a C60 core

Fairly pure hexaadducts of molecular weights ranging from 2 × 104 to 2 × 106 could be prepared by reacting polystyryllithium with C60 in toluene. These star-shaped polymers, with a fullerene core, associate a low polymolecularity of the arms (I < 1.1) and a fairly good control of the functionality (6). Their behavior in toluene has been established using static and dynamic light scattering as well as viscometric measurements. The dimensions of these star-molecules in this good solvent, normalized by the dimensions of the arm or by that of linear polystyrene of same molecular weight, are in agreement with those expected for stars with six arms. Upon decreasing the molecular weight from 2 × 106 to 5 × 105, an evolution from a random coil type behavior toward that of a dense sphere can be observed.

Reaction of “living” poly(ethylene oxide) chains with C60

Abstract To determine the reactivity of fullerene toward oxanions, we have studied the grafting of “living” poly(ethylene oxide) (PEO-K+) and ethylene oxide “capped” polystyrene chains (PSCH2CH2O-K+) onto C60 in THF. We demonstrate that, in this polar solvent, electron transfer from the oxanion to the highly electron accepting fullerene takes place. This transfer is limited to two electron per fullerene, and is accompanied by addition of polymer chains onto the C60 probably through grafting of the generated radicals. SEC characterization of (PEO)XC60 indicates the presence of products with molar masses corresponding to X≥6. That may result from aggregation occurring in this case as, using the same active species, practically only mono- and di-adducts are obtained if the chain is PS.

Grafting polymers onto C60 via an atom transfer reaction

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 60 . 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.

Thermal stability of a C60-polystyrene bond

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°C, 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.

Potassium-doped polyacetylene: Influence of redox potential of dopants on doping level

Abstract Polyacetylene (PA) films, from ten different syntheses, were n-doped with 14 organopotassium compounds including carbanions and radical-ion salts in tetrahydrofuran (THF). The maximum doping level for a given dopant is higher for cis than for trans isomer and is relatively independent of film synthesis conditions. The measured doping levels correlate well with the redox potential of dopants when these values are available. This allows a thermodynamic control of the chemical doping level over a wide range. Inversely, our classification by increasing doping efficiency allows a new semiquantitative scale to be established of oxidation potential of highly reactive carbanionic salts for which no data are available yet.

Experimental studies of n-doped (CH)x: D.c. electrical conductivity

Abstract The d.c. electrical conductivity of n-doped (CH) x was studied as a function of the doping level at 25°C. The dopants were sodium-naphthalene, lithium and sodium benzophenone dianionic salts in tetrahydrofuran (THF). Details of the experimental procedure are described. It was discovered that the THF vapour pressure present in the atmosphere in contact with the doped film drastically increases the film conductivity, at low doping levels. This may be due to an effect of the solvation state of cations. Conductivity measurements were also performed at very low doping levels (evaluated from metallic infrared bands) on (CHNa y ) s , (CDNa y ) x and (CDK y ) x . A mobility value of 4 × 10 −6 cm 2/ rmVs was deduced for 57% trans -(CHN iny ) x .

Dicumylbarium. A novel initiator in anionic polymerization. Its physicochemical properties in tetrahydrofuran and tetrahydropyran

Abstract The preparation of dicumylbarium by reaction of methyl cumyl ether with finely-divided barium in tetrahydrofuran (THF) and tetrahydropyran (THP) is described. The salt was characterized by spectrophotometric and chemical methods. Conductance studies for 10−3 to 10−5M concentrations of the salt in THF at temperatures from 15 to −70°C and in THP from 15 to −30°C demonstrated the presence of triple ions in thermodynamic equilibrium with free ions and pairs. In THF the dissociation constant varies from 1.0 × 10−9M at 15°C to 2.3 × 10−9M at −70°C, the corresponding enthalpy and entropy of reaction being −1.1 kcal mol−1 and −45 e.u. respectively. In THP, however, dissociation of the salt is too weak to be determined directly. Kinetic studies of the protonation reaction between dicumylbarium and triphenylmethane in THF showed that the apparent rate of reaction is 1.65 × 10−5 sec−1, independent of carbanion concentration. This indicates that protonation proceeds exclusively via free ions and hence provides further evidence for the presence of triple ions in dicumylbarium solutions.

Kinetics of chemical n-doping of polyacetylene

Abstract Polyacetylene (PA) films were doped with tetrahydrofuran and benzene solutions of organo potassium and lithium compounds. The kinetics for doping were determined from the variation of the dopant concentration with time, as a function of film thickness, dopant concentration and doping temperature. The experimental doping rates were compared to computed values deduced from a doping model taking into account the interfibrillar diffusion, separately measured with an inert hydrocarbon. This comparison allows a minimum value (10−15 cm2/s) to be determined for the intrafibrillar diffusion coefficient Df of doped sites and cations. With such a value no homogeneous doping can be carried out at intermediate doping levels, for films thicker than about 50 microns, by a simple control of doping time or dopant concentration. This may, however, be achieved by a thermodynamic control using dopants of suitable redox potential.

Controlling the Number of Arms of Polymer Stars with a Fullerene C60 Core

Abstract Pure di‐ and tetra‐adducts can be obtained by grafting polystyrene (PS) chains onto C60 via an atom transfer radical addition. Stars with a C60 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 be prepared by controlling the stoichiometry PSLi/C60. 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.