Abstract: The crystal structure of the CHCl₃-soluble fraction (low molecular weight) of chemically prepared polytbiophene(PT₁) has been investigated using WAXD and TGA techniques. Ruland's method has been used to calculate its crystallinity. Heat treatment for 30 min. at 150℃ in N₂ leads to a significant increase in crystallinity and crystallite size of polymer. From the crystal-lographic data although incomplete at present time, a preliminary model of the polymer structure has been proposed. The results are in consistence with those devised from an orthorhombic or a monoclinic unit cell. In either case the polymer chain axes are found to be along the c-axis. The calculated density is approximately 1.55g/cm³ assuming two chains per unit cell. The preliminary density value of the sample is 1.18g/cm³ in satisfactory agreement with the calculated value since the density of the partially amorphous material is expected to be less than that of the full crystalline polymer. An individual chain structure for PT₁ in which the thiophene units alternate on both sides results in straight chain conformation. FTIR spectra of unannealed and annealed PT₁ powder have been assigned.

Key words: Crystal structure, Polythiophene, Conductive polymer, X-ray diffraction, Heat treatment