Structural properties of doped polyacetylenes

Abstract

Among polymers that become highly conducting upon doping, polyacetylene, (CH)_x, plays a special role: this simplest conjugated polymer can be obtained under high crystallinity, which gives the opportunity to study the relationship between structural and electrical properties. However polyacetylene cannot be obtained as single crystals, at least up to now, but under the form of films constituted of randomly distributed fibers with diameters ranging from about 200 A to 500 A. The fibers can be more or less aligned preferentially, for example by stretching the films. Nevertheless, X-ray spectra show only Debye-Scherrer diffraction rings, which in addition are limited in number (10 to 12). Thus the general approach consists in imagining a structural model a priori and then in comparing observed positions and intensities of diffraction peaks with those calculated from the model. Also of interest are lattice packing calculations and analysis of molecular packing in model compounds.