R. Nuffer

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.

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.

Preparation of networks with C60 knots using anionic polymers.

Abstract Two methods to prepare controlled three dimensional structures including Cso molecules as knots are described. For the first network synthesis, THF soluble C 60 2− (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 C 60 . The second method, developed to increase the functionality of the knots, consists of reacting C 60 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.

Palm-tree and dumbbell like polystyrene structures based on C60

Abstract By reacting anionic polymers such as polystyryllithium with C 60 , “living” hexa-adducts have been prepared and used to initiate the anionic polymerization of vinyl monomers. If styrene is used as the monomer, only one chain is growing out from the fullerene core producing a “palm-tree” type structure. The outgrowing chain bearing on its end a carbanion, could be reacted with the coupling agent dibromoparaxylene to form “dumbbell” like macromolecules where two 6 branched PS stars are connected together by a PS chain of controlled length.

C60 as core of well defined hetero-star polymers

Abstract Addition of “living” polymers such, as polystyryllithium onto C60 allows the synthesis of well defined star-shaped macromolecules with a C60 core bearing six PS arms of about same length and an equal number of negative charges located on the fullerene. If these latter are used to initiate the anionic polymerization of methymethacrylate, a hetero-star consisting of a C60 core With 6 polystyrene and 2 poly(methylmethacrylate) arms is obtained. A second way to prepare hetero-stars is to react the “living” stars with functional polymers bearing at one end a reactive halide. We were able to graft 2 additional PS chains of exactly the same or different, ^ length as the 6 branches of the starting 6-branch star, producing respectively a 8 branched star or asymmetric-star.

Synthesis of polyacetylene and styrene-PA block copolymers by chemical modification of phenylvinylsulfoxide

Abstract Polystyrene-polyacetylene block copolymers with narrow molecular weight distributions were prepared by heating copolymers containing poly(phenylvinylsulfoxide) (PPVS) sequences. The length of the conjugated sequences depends on the heating temperature. The transformation from PPVS to PA was studied by spectrophotometry. The PS-PA copolymers become soluble when the PS block is large enough. These compounds can be doped, as illustrated by the change in their UV-Vis-NIR and IR spectra.

THF insertion in n-doped polyacetylene

Abstract The residual coinsertion of THF in polyacetylene (PA), n-doped by THF solutions of organo lithium, sodium and potassium, has been quantitatively analysed after cryogenic pumping (at −80 °C and −196 °C) of samples kept at room temperature. It is found that the amount of coinserted THF per CH increases with the doping level y up to a maximum of y = 8–10% and then decreases. This maximum increases when the size of the cation decreases, from K to Li. With Na and K, and for any doping level, the THF content is higher in cis -doped than in trans -doped samples, while with Li no difference is observed between the two isomers. The influence of solvation on properties is discussed. A synergic effect was observed during solvation by a THF/toluene mixture.