Nature of the double melting peaks of regioregular poly(3-dodecylthiophene)

The structure evolution of poly(3-dodecylthiophene) (P3DDT) during heating was investigated by differential scanning calorimetry (DSC) and in-situ wide and small-angle X-ray scattering (WAXS/SAXS). Four regions were classified in the heating process, i.e. below the melting temperature of the side chain (I), side-chain melting region (II), below main chain melting region (III) and the melting of the main chain region (IV). Melting of side chains in region II introduced an expansion of the (1 0 0) plane spacing, resulting in a lower crystalline phase density and therefore a lower crystalline/amorphous density contrast. The reorganization process during heating was observed. The double melting peaks during heating were shown to result from melting and recrystallization. No evidence of liquid crystalline phase or mesophase was observed above the melting temperature of P3DDT.