DOPING KINETICS OF POLYACETYLENE IN THE SHORT RANGE

Abstract

E. Cernia, L. D'llario* E. Ferretti and G. Nencini ASSORENI, 00015 Monterotondo (Rome), Italy Resume - La cinetique du dopage avec I de films de polyacetylene (PA), obtenus par la methode de Shirakawa /l/, a ete etudiee dans les premieres minutes du contact entre le dopant et le PA en suivant la variation des proprietes electriques de conductivite et spectroscopique d'absorbance IR a 1400 Cm et a 1023 et 750 cm~ . Les donnees experimentales ont mis en evidence l'existence, dans cet intervalle de temps, de au moins trois etapes de reaction caracterisees par des constantes cinetiques qui different par des ordres de grandeur. On a essaye d'elaborer un modele cinetique du processus de dopage et on a calcule les valeurs des energies d'activation. Abstract - The kinetics of doping with iodine of Polyacetylene (PA) films, synthesized by the Shirakawa technique /l/,e bee hav n investigated by measuring the variation of electrical conductivity and IR absorbance at 1400, 1023 and 750 cm within the time range of the first minute of doping. The experimental data suggest that the doping process occurs within at least three steps whose rate constants differ by orders of magnitude. An attempt is made to elaborate a kinetic model for the doping process and the activation energies are calculated. INTRODUCTION PA was synthesized for the first time in 1958 by the Natta group /2/, but only in 1977 Heegher and Shyrakawa /3,4/ showed that, by doping a PA film with several chemical agents, one could obtain a polymeric material with electrical properties ranging from the insulator to the metallic state. Many physical, chemical and structural /5-12/ studies have been carried out on this material, shading light on its interesting nature and properties. Impurities, oxygen and thermal effects all make difficult the handling of this polymer and cause possible large error of measurement. We have then tried to have a sufficient number of data in order to estimate the measurement reproducibility on the variation of electrical conducti­vity in the initial stage of the doping process of PA. EXPERIMENTAL PA films were sinthesized in the ASS0RENI Laboratories of S. Donato Milanese following the Shyrakawa technique /l/. Catalist residues, after washing, were present as ~ 1.0% . The thickness of the films was-^30 f and cis content was 42.4% and 24.2%, as determined by the Ito procedure /13/. The iodination of the sample was done in vapour phase, allowing thermalization of the I before reaching the sample. Experiments were carried out either in vacuum either under helium flow. *Present address : Istituto di Chimica Fisica - Universita di Roma - 00100 Rome, Italy Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983333