Polymorphism and Structural Transition around 54 °C in Regioregular Poly(3-hexylthiophene) with High Crystallinity As Revealed by Infrared Spectroscopy
Аннотация:Poly(3-hexyllthiophene) (P3HT) with high crystallinity was prepared by controlling the solvent evaporation rate together with the aid of chloroform vapor annealing. According to the infrared spectroscopy combined with the thermal analysis and the X-ray diffraction (XRD) data, a new crystal modification named as form I′ was identified for P3HT sample crystallized under extremely slow evaporation rate at low temperature (13 °C). Such crystal modification has shorter interlayer distance than that of the more common but more disordered form I of P3HT. Moreover, it demonstrates a distinct endothermic peak around 54 °C and a characteristic IR band at 823 cm–1, which have never been reported for P3HT in the literature. The origin of the structural transition around 54 °C is investigated in detail by temperature-dependent infrared spectroscopy combined with the in situ synchrotron WAXD measurement. It is found that, during the heating process of P3HT form I′ crystal, there is the form I′-to-form I phase transition from 30 to 60 °C, which belongs to the solid-to-solid phase transition.
