STRUCTURAL AND THERMOCHROMIC PROPERTIES OF MIXTURES OF POLY(3-HEXYLTHIOPHENE) AND POLY(3-OCTYLTHIOPHENE)

For the first time, the structural and thermochromic properties of mix tures of poly(3-hexylthiophene) (PHT) and poly(3-octylthiophene) (POT) have been studied. X-ray diffraction and optical absorption spectrosc opy were employed, the latter on spin-cast films in the temperature ra nge 20-210-degrees-C. The results show that the mixtures are single-ph ase materials that are structurally intermediate between PHT and POT. It was found that the longest interchain distance a in the crystalline part of the polymer and the thermochromic transition temperature T(t) both vary nonlinearly with composition in such a way that T(t) and a are approximately linear to each other. This indicates that the side c hains act primarily as spacers between main chains, rather than being directly involved in the thermochromic transition. This transition may instead be induced by a melting of the polymer backbone.