Multiple Chain Packing and Phase Composition in Regioregular Poly(3-butylthiophene) Films

Journal article, 2016

On the basis of different film preparation conditions, we address the phase composition and thiophene main-chain and butyl side-chain organization of three regioregular poly(3-butylthiophene) (P3BT) samples prepared by drop-casting. These samples are readily identified by wide-angle X-ray diffraction (WAXD) with the structural P3BT polymorphs commonly referred to as forms I, I?, and II. Here, we show by means of WAXD, solid-state nuclear magnetic resonance (NMR), and Fourier-transform infrared spectroscopy (FTIR) that the P3BT samples identified with these polymeric forms (I, I?, and II) do not contain a single, unique crystalline phase and an amorphous phase, but additionally consist of one (form II) or two (forms I and I?) distinct crystalline phases. Each of the crystalline phases is associated with specific thiophene main-chain packing arrangements and butyl side-chain organizations. We provide a spectroscopic identification for each of the P3BT crystalline phases, enabling a detailed and consistent picture of molecular order and polymer main-chain and side-chain packing. Thus, our results are expected to be valuable in future studies of poly(3-alkylthiophene) (P3AT) thin films, where in particular FTIR studies will permit quick and easy access to both phase composition and identification of multiple thiophene main-chain packing structures.