X-RAY-DIFFRACTION STUDY OF OCTYLPHENYL-SUBSTITUTED POLYTHIOPHENE

A series of regioregular Poly(3-(4'-octylphenyl)thiophene)s (POPT), pr oduced 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 t reatment in chloroform vapor. Polymer films cast from chloroform solut ion were found to he oriented with their side chains directed normal t o the glass substrates. The diffraction patterns indicate that the pol ymers, both in the amorphous and crystalline phase, pack as relatively straight chains with a long conjugation length as revealed by absorpt ion measurements. The crystalline phase is characterized by a layered structure in which stacks of planar thiophene main chains are uniforml y spaced by the side chains. This structure resembles closely the one of poly(3-octylthiophene), though the stacking distance and the repeti tion distance along the side chains is increased by the presence of th e additional phenyl group.