Macromolecules, 2018, vol 51, 20, pp. 8306-8315
Understanding the deformation mechanism of conjugated polymers is essential for developing flexible or stretchable electronic devices. In this work, the mechanical properties of poly(3-dodecylthiophene) (P3DDT) and poly(3-hexylthiophene) (P3HT) are measured at different temperatures, and the underlying deformation mechanism is explored by using in situ X-ray scattering and pole figure. It is observed that the modulus and fracture strength of P3DDT decrease with increasing stretching temperature. The elongation at break of P3DDT exhibits a sharp increase when the stretching temperature reaches 45 °C. The general deformation process of the two polymers is in line with the traditional deformation mechanism established for flexible crystalline polymers with several special features. Well-defined yielding is not detected even at temperatures below the main-chain glass transition temperature, which corresponds to the microscopic observation of the absence of a well-defined lamellar–fibrillar transition. By analysis of the orientation features, P3DDT and P3HT show different orientation features at 30 °C while they exhibit similar c-axis orientation at 110 °C. Crystallographic slip is proposed to be the main deformation mechanism at 30 °C, while evidence for stress-induced melting and recrystallization is observed at 110 °C.