Optimisation des conditions de transformation du poly(phénylvinylsulfoxyde) en poly(acétylène)

Institut Charles Sadron, CRM-EAHP, CNRS-ULP, 6, rue Boussingault, 67083 Strasbourg Cedex, France.

Résumé

Des chaînes linéaires de poly(acétylène) (PA) de longueur contrôlée ont été obtenues par chauffage de poly(phénylvinylsulfoxyde) (PPVS) préparé anioniquement. L’étude de cette transformation par spectrophotométrie IR et UV/Vis montre qu’en diminuant la température, la longueur des séquences conjuguées obtenues augmente. Les séquences les plus longues sont obtenues vers 50-60°C, la vitesse de conversion devenant trop faible pour les températures inférieures. Ces PA (ex-PPVS) ont été dopés n et p.

Abstract

Linear polyacetylene with defined chain length were obtained by heating anionically prepared polyphenylvinylsulfoxides. In order to determine the best conditions for the synthesis of this PA, we studied the thermal transformation by spectrophotometry. The appearing of an isosbestic point in the UV/Vis spectra, for an isothermic treatment, proves that this transformation corresponds to a simple reaction. During this conversion, the position of the absorption maximum relative to the conjugated product, directly related to the conjugation length, does not move; this indicates a "zip" mechanism. The conjugation length can be increased by decreasing the conversion temperature. The best results are obtained around 50-60°C, the kinetics becoming too slow at lower temperatures. This observations can be interpreted by assuming that lowering the temperature decreases the number of "zip starting sites" created on the chain, without decreasing the "zip propagation rate" in the same proportion. The UV/Vis/NIR characterization of the n and p doped compounds indicates that for low doping levels, the longest sequences are doped preferencially.