P. Audebert

Modified electrodes from organic-inorganic hybrid gels formed by hydrolysis-polycondensation of some trimethoxysilylferrocenes

Abstract Gels formed from trimethoxysilylferrocene 1 and 1,1′-bis(trimethoxysilyl)ferrocene 2 copolymerized with tetramethoxysilane have been deposited onto platinum, and allow the building of modified electrodes with interesting electrochemical properties. The electrochemical response of the gels has been found to be strongly dependent on the starting molecule and its concentration, but only weakly on the electrolyte nature. Special attention has been paid to the dynamics of the electron transfer through the gels, and a quantitative analysis has been performed in various cases. While the gels prepared from the disilylated ferrocene 2 display, like several different functionalized polymers, a Cottrellian diffusion of the charge transfer (in accordance with the classical theoretical treatment of Andrieux and Saveant), in the gels formed from the monosilylated ferrocene 1, the charge transfer follows a power law with a fractional exponent. This unique behaviour is indicative of a particular substructure in the gels, with the ferrocene moieties probably positioned at the surface of accessible silica particles.

Vapor deposition polymerization and reactive ion beam etching of poly(p-xylylene) films for waveguide applications

Vapor deposition polymerization (VDP) of parylene-n and parylene-c films has been studied in terms of the initial evaporated monomer mass: controlled and homogeneous film thicknesses are obtained provided that the vapor flow is low. In order to use these materials for ribbon waveguide applications, reactive ion beam etching of the films has been tried, giving very low etching speed.

Insights into the polymerization kinetics of some α-silylated thiophene oligomers

Abstract Oxidation of several silylthiophene oligomers has been studied in dichloromethane and acetonitrile by cyclic voltammetry. Detailed mechanistic studies show that the oxidative coupling of silyloligothiophenes involves the carbon-carbon bond formation between two cation-radicals, as previously observed for other non-silylated oligothiophenes. The lifetimes of the cation-radicals are found to be dependent on the solvent, indicating a nucleophilic assistance to the Cue5f8Si cleavage. This behavior is in agreement with a reversible coupling step leading to the formation of a dimeric cation followed by the irreversible cleavage of the Cue5f8Si bond. Evidence for the existence of an equilibrium between the monomeric cation-radical and an associated form (π-dimerization) has been obtained from the variation of the redox potential with the temperature and concentration for the most stable cation-radical.

Kinetic behaviour of an amperometric biosensor made of an enzymatic carbon paste and a Nafion® gel investigated by rotating electrode studies

Abstract An amperometric glucose sensor (β- d -glucose) incorporating the biocatalytic properties of an enzyme, glucose oxidase (GOD), and the membrane properties of a hydrophobic Nafion® gel was constructed. The kinetic features of the current provided by the sensor were investigated by rotating electrode steady state experiments.

Electrochemical studies of the oxidation of sterically hindered pyrroles and thiophenes

Abstract The electrochemical oxidation of several α,α′-di- tert -butyl pyrroles and thiophenes has been investigated in acetonitrile. Reversible cyclic voltammograms for the oxidation of one-ring α,α′-di- tert -butyl thiophenes or pyrroles were obtained at low scan rates (0.05–5 V s −1 ), indicating a large stability of their cation-radicals. Chemical evolutions without polymerization of the cation-radical were observed at longer time scales. The formal potentials E o and electron exchange standard rate constants k s were determined and compared with preceding reports for the unsubstituted analogues. From the substituent variations, the E o values for the oxidation of the unsubstituted thiophene and bithiophene were estimated as + 1.97 and + 1.49 V(SCE) respectively.

Electrochemical properties of some benzoxazines: conditions for electropolymerization in alkaline medium

Abstract The electro-oxidation of three isomeric methyl benzoxazines has been studied in acetonitrile and methanol in either neutral or alkaline media. Oxidation potentials have been determined and the reactivity of the benzoxazine cation radicals estimated. In alkaline methanol, the mechanism changes in favour of oxidation of the benzoxazine anion, and formation of a thin polymer layer is observed on metallic substrates. The resulting polymers were analysed by X-ray photoelectron spectroscopy measurements and a polymer formula has been proposed.

Electrochemical oxidation of some enol silyl ethers; investigations on the reactivity of cyclizable cation-radicals

The electrochemical oxidation of several silyl enolethers (SE) formed from a variety of differently substituted α- or β-tetralones by side chains is described. The behaviour of the cation radicals of the SE has been found to be strongly dependent on the substituted lateral chain, especially when the substituent contains a cyclizable group like a double bond. The difference between the oxidation potentials has been attibuted to the occurence of a first order chemical reaction between the cation radical and the substituent, which is probably a cyclization reaction. The relative rates of this reaction have been discussed in relation to the substituent.