Correlation between structure and composition of hexylthiophene-octylthiophene copolymers studied by X-ray diffraction

X-ray diffraction has been used to study the structures of two oriented hexylthiophene-octylthiophene copolymers as functions of the hexylthiophene-to-octylthiophene ratio. The results show that the samples are partially crystalline with structures intermediate between those of the homopolymers poly(3-hexylthiophene) and poly(3-octylthiophene). In the crystalline part, stacks of thiophene chains, equally spaced by the side chains, form a lamellar structure. The distance between adjacent stacks is found to vary linearly with the mole fraction of octylthiophene.