Twist glass transition in regioregulated poly(3-alkylthiophene)

The molecular structure and dynamics of regioregulated poly(3-butylthiophene) (P3BT), poly(3-hexylthiophene) (P3HT), and poly(3-dodecylthiophene) (P3DDT) were investigated using Fourier-transform infrared absorption (FTIR), solid-state C-13 nuclear-magnetic resonance (NMR), and differential-scanning calorimetry (DSC) measurements. In the DSC measurements, the endothermic peak was obtained around 340 K in P3BT, and assigned to enthalpy relaxation that originated from the glass transition of the thiophene-ring twist in crystalline phase from results of FTIR, C-13 cross-polarization and magic-angle spinning (CPMAS) NMR, C-13 spin-lattice relaxation-time measurements, and centerband-only detection of exchange (CODEX) measurements. We defined this transition as a twist-glass transition, which is analogous to the plastic crystal-glassy crystal transition.