Hervé Cheradame

Poly(dimethylsiloxane)-poly(ethylene oxide) based polyurethane networks used as electrolytes in lithium electrochemical solid state batteries

Abstract Ionic conductivity and redox stability domain of a new type of polymer electrolyte have been studied. The polymer electrolytes were prepared from a network of poly (dimethylsiloxane-grafted ethylene oxide) copolymer crosslinked by an aliphatic isocyanate (grafted PDMS) and containing 10 wt% LiClO 4 . Ionic conductivities higher than 10 −5 ω −1 cm −1 are obtained above 30°C. The study of the electrochemical stability of the crosslinking agent suggests that the unreacted isocyanate groups are not stable. The electroactivity domain of the grafted PDMS-LiClO 4 10 wt% electrolyte is larger than 3 V. The performances of a solid state battery using this electrolyte have been investigated. The first discharge and charge depths were 73%. The rechargeability behaviour have been compared with those of a Li/RuO 2 battery with a linear high molecular weight P(EO) 8 -LiClO 4 as electrolyte.

Crosslinking of polyether networks by hydrosilylation and related side reactions

Abstract The synthesis of a well defined poly(ethylene oxide) network is described. This was achieved by performing hydrosilylation of α,ω-diallyl PEO with 2,4,6,8-tetramethyltetrahydrocyclosiloxane (D 4 H). The influence of several factors, including the nature of the catalyst, temperature, (SiH)/(double bond) ratio and traces of water, on the hydrosilylation reaction is described. Side reactions were studied by 1 H and 29 Si n.m.r.

Cationic transport numbers in polyether-based networks containing lithium salts

Abstract Measurements of the Li + transport number by the Tubandt method on solid electrolytes based on polyethers crosslinked with triisocyanates containing various lithium salts gave values consistently indicating the predominance of anionic conduction. Transport numbers ( t + ) were found to be temperature independent between 70 and 120 °C, but to decrease as the salt concentration increased. The other parameters studied were the nature of the anion and the structure and length of the polyether segments.

Correlation among transport properties in ionically conducting cross-linked networks

Abstract Examination of the quantitative correlation between the ionic conductivity and the dynamic mechanical properties of cross-linked polyether networks filled with an inorganic salt supports the assumption that mobile ions and chains segments need the same free volume fraction for their diffusion. The spin-spin relaxation time of the different nuclei belonging either to the macromolecular chains or to the ionic species exhibits the same free volume dependence. From the study of the conductivity variations with respect to salt concentration it is concluded that its dissociation is probably complete even at relatively high concentration.

The Use of 2,6-Di-tert-Butyl-4-Methylpyridine to Distinguish Between Different Modes of Initiation in Cationic Polymerisation

Summary2,6-Di-tert-butyl-4-methylpyridine (DBMP) effectively discriminates between the two major initiation mechanisms encountered in cationic polymerisation. Whenever a protonic acid is involved in the formation of chain carriers, directly or through cocatalysis, addition of equivalent amounts of DBMP inhibits the process. If however direct electrophilic addition of a Lewis acid to the monomer is the source of active species, the hindered base cannot intervene to alter its course. When both pathways are operative DBMP only quenches the former and provides a means of assessing the relative importance of each. Examples are given of the three situations. The simplicity of the method is emphasised.

Investigation of the oxidative cleavage of butyl rubber by selective catalysis

Abstract Selective oxidizing cleavage of carbon-carbon double bonds of unsaturated polymers leads to bifunctional oligomers. It is shown, using ruthenium tetroxide in catalytic amount in conjunction with a peracid as co-oxidizing agent, that efficient cleavage of butyl rubber double bonds can be obtained without side reaction. The procedure can be used for analytical as well as for synthetic purpose.

Correlation between ionic conductivity and7Li-NMR of polyether-polyurethane networks containing lithium perchlorate

SummaryThe effect of temperature on the ionic conductivity and the7Li NME line width of a polyether-polyurethane network containing lithium perchlorate was studied. A treatment of the results based on free-volume principles yielded a linear correlation between the logarithm of the reduced conductivity, бT /бT0, and the logarithm of the reduced7Li NMR line width, δT/δT0, for a given reference temperature, To=323 K.

α-ω-Bifunctional oligomers from copolymers of conjugated dienes with isobutene

Abstract The selective oxidative cleavage of unsaturated copolymers of isobutene with conjugated diene using ruthenium tetroxide has been carried out, giving various bifunctional oligomers. A comparison between molecular weight determination and microanalysis seems to show that the nearly perfect bifunctionality obtained for the cleavage of 2,3-dimethylbutadiene-isobutene copolymer is due to the almost enclusive 1–4 configuration of the diene unit in the copolymer; some non-1–4 incorporation is apparent in the case of 1,3-pentadiene.

Poly(vinyl chloroformate) and its derivatives: 5. New poly(vinyl carbamates) and poly(vinyl thiocarbonates)

Abstract New poly(vinyl carbamates) and poly(vinyl thiocarbonates) have been prepared either by free radical polymerization of monomers or by chemical modification of poly(vinyl chloroformate) with appropriate amines and thiols using phase transfer catalysis. The structure of these polymers has been examined by i.r. and 13 C n.m.r. spectroscopy and their thermal behaviour has been studied.

Mechanism of high ionic conductivity in elastomeric networks

Abstract The viscoelastic properties and the ionic conductivity of polyether-polyurethane networks containing alkali metal salts have been studied at various temperatures, salt concentrations and network structures. The reduced temperature, TT g , is the predominant parameter which governs the viscoelastic behaviour and the ionic conductivity of these networks. Using the free volume concept an expresssion is derived for the ionic conductivity, irrespective of the macrostructure involved. The logarithm of the reduced conductivity, σ T /σ T R (which is the ratio of the conductivity at a given temperature to that at the reference temperature), is a linear function of the shift factor, log a T , given by the dynamic mechanical properties. A comparison is made between the WLF parameters C 1 and C 2 , obtained from conductivity and viscoelastic measurements.