Dresden 2011 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 15: Organic Semiconductors III: Aggregation and Nanostructures (jointly with HL, DS)
CPP 15.3: Vortrag
Dienstag, 15. März 2011, 14:30–14:45, ZEU 222
High Crystallinity and Nature of Crystal–Crystal Phase Transformations in Regioregular Poly(3-hexylthiophene) — •Ovidiu F. Pascui1,3, Ruth Lohwassser2, Michael Sommer2, Mukundan Thelakkat2, Thomas Thurn-Albrecht1, and Kay Saalwächter1 — 1Institut für Physik, Martin-Luther-Univ. Halle-Wittenberg, Halle, Germany — 2Makromolekulare Chemie I, Universität Bayreuth, Germany — 3Experimentelle Physik III, TU Dortmund, Germany
Molecular weight and stereoregularity affect the morphology and the crystallinity of conjugated polymers and are thus of pivotal relevance for the mobility of charge carriers in electro-optical device applications. We use 13C solid-state NMR to determine the crystallinity and details on crystal–crystal phase transformations in regioregular head-to-tail poly(3-hexylthiophene) of well-defined molecular weight and demonstrate that the crystallinity was previously severely underestimated. Typical crystallinities are at least around 37% for the lowest molecular weights and as high as about 64% upon increasing MW, corresponding to a corrected maximum value for the reference melting enthalpy of Δ Hm ≈ 37 J/g for use in DSC experiments. Using one- and two-dimensional NMR, we observe that the crystal-crystal phase transition between a 3D- and a 2D-ordered crystalline phase at around 60∘C entails a structural disordering process of the alkyl side chains, while not affecting the backbones. The formation of the 3D-ordered phase is kinetically suppressed at higher molecular weights.
see: O. F. Pascui et al., Macromolecules 43, 9401 (2010).