SIDE-CHAIN ORDER IN POLY(3-ALKYLTHIOPHENES)

The structures of unoriented films of poly(3-alkylthiophenes) were studied by X-ray diffraction, infrared spectroscopy, and organic vapor sorption. Side-chain crystallization takes place in these films when the alkyl groups contain 12 or more carbon atoms. The disordering of the side chain upon melting results in a large increase in the amount of hexane vapor absorbed by poly(3-tetradecylthiophene) (PTDT) when the temperature is raised to above the melting point. The effective distance of side-chain overlap, as measured by hexane as the diffusional probe, is estimated to be 6.7 angstrom along the a-axis. The distance of overlap is about 2.6 angstrom for poly(3-octylthiophene) (POT). When the conformational information obtained from infrared spectroscopy is combined with the results of X-ray and vapor sorption studies, a model can be constructed which accounts for all the experimental observations.