The Effects of Regioregularity on the Thermotropic Liquid Crystalline Phase Transitions of Poly(3-dodecylthiophene)

We investigate the thermotropic liquid crystalline (LC) phase transition of regioregularity (RR)-controlled poly(3-dodecylthiophene) (P3DDT). Controlling RR of the P3DDT from 95 to 65% provides significantly altered strength of the LC interactions while maintaining the chemical structures the same. As the RR decreases, the P3DDT exhibits progressively decreased phase transition temperatures under polarized microscopy due to weaker interchain interactions. In the X-ray scattering and thermal analysis, the melting of side-chain and backbone leads to entering the nematic and isotropic phases, respectively. Furthermore, as RR decreases, the ratio of Form II/Form I polymorphs increases. Considering the faster breakdown of Form II upon heating, larger Form II/Form I can promote lower transition temperature. Molecular design of the RR provides an effective approach to control the LC interactions and the morphologies of the conjugated polymers.