Dresden 2009 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 40: POSTERS Electronic and Optical Properties
CPP 40.9: Poster
Donnerstag, 26. März 2009, 17:00–19:30, P3
About the molecular weight and temperature dependence of the microstructure of regioregular poly(3-hexylthiophene) — •Zhiyong Wu1, Albrecht Petzold1, Thomas Thurn-Albrecht1, Ruth Lohwasser2, Michael Sommer2, and Mukundan Thelakkat2 — 1Institut für Physik, Martin-Luther-Universität Halle-Wittenberg — 2Makromolekulare Chemie I, Universität Bayreuth
We report about structural investigations of a series of regioregular poly(3-hexylthiophene) (P3HT) with different, well defined molecular weight using a combination of x-ray scattering techniques (WAXS, SAXS) and calorimetry (DSC). The semicrystalline structure of P3HT shows a complex temperature dependence. It undergoes a solid-to-solid phase transition at around 60°C and melting occurs in two steps with an intermediate layered structure with smectic symmetry. Wide angle x-ray diffraction (WAXD) experiments give evidence for an orthorhombic crystal unit cell consistent with previous reports in the literature. We propose a structure at room temperature with polyethylene-like packing of the side chains tilted with respect to the main chains and without interdigitation. At the phase transition side chain melting occurs and the side chains acquire a disordered state. The corresponding ordering process during cooling is kinetically hindered for higher molecular weight. DSC measurements show, that the melting temperature as well as the enthalpy of melting strongly increase with increasing molecular weight, indicating an increase both of the thickness of the crystallites and of the crystallinity. This result is confirmed by direct structural analysis using small angle x-ray scattering.