X-RAY-DIFFRACTION STUDY OF OCTYLPHENYL-SUBSTITUTED POLYTHIOPHENE

A series of regioregular Poly(3-(4'-octylphenyl)thiophene)s (POPT), produced with a varying ratio of monomer to coupling agent (FeCl3), was studied by X-ray diffraction. The results show that POPT is a polymer with a low degree of crystallinity, which could be increased by using a more gentle polymerization condition and further increased by heat treatment in chloroform vapor. Polymer films cast from chloroform solution were found to he oriented with their side chains directed normal to the glass substrates. The diffraction patterns indicate that the polymers, both in the amorphous and crystalline phase, pack as relatively straight chains with a long conjugation length as revealed by absorption measurements. The crystalline phase is characterized by a layered structure in which stacks of planar thiophene main chains are uniformly spaced by the side chains. This structure resembles closely the one of poly(3-octylthiophene), though the stacking distance and the repetition distance along the side chains is increased by the presence of the additional phenyl group.