Metallic polymer composites with bis(ethylenedioxy)-tetrathiafulvalene salts. Preparation–properties relationship

The relationship between preparation conditions and properties of surface-conductive composites obtained by crystallization of low molecular weight organic conductors in polymer matrices (reticulate doped polymers) is investigated. By optimization of the preparation procedure we have obtained the first organic conductive composites which show metallic surface conductivity without any additional treatment. Surface-conductive polycarbonate (PC) films with bis(ethylenedioxy)-tetrathiafulvalene (BEDO-TTF) salts with iodine and bromine as the additives were obtained by the two-step reticulate doping method. BEDO-TTF content in PC was 1 wt.%. Due to the strong tendency of BEDO-TTF to form organic metals the films obtained under optimum conditions show exceptionally high surface conductivity (even above 10−3 S/□ for both I and Br salts), and exhibit metal-like temperature dependence of conductivity in a broad temperature range (even down to at least 10 K). Depending on the preparation conditions (vapour composition, treatment time) it is also possible to obtain highly conductive films showing semiconductor-like temperature dependence or metal–insulator transition. Structure and morphology of the conductive network is characterized using scanning electron microscopy and X-ray diffraction. These results and optical absorption studies permit identification of the salts which are main components of the networks in most of the systems. When the conductive network is made of BEDO-TTF/Br salts the films show also exceptionally high transparency.