Berlin 2001 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 16: Poster: Dynamics of Molecular Systems, Polymer Dynamics, Glass Transition, Crystallization, Electronic Properties of Polymers

CPP 16.11: Poster

Montag, 2. April 2001, 12:30–15:00, AT1

Time and Length Scales in Amorphous Poly(ethyl-methacrylate) Melts Revealed by Solid-State NMR Spectroscopy — •Robert Graf¹, Michael Wind¹, Lothar Brombacher¹, Werner Steffen¹, Andreas Heuer², and Hans W. Spiess¹ — ¹Max-Planck-Institut für Polymerforschung, Postfach 3148, 55021 Mainz — ²Westfählische Wilhelms-Universität Münster, Schloßplatz 2, D-48149 Münster

The current knowledge of structure and complex dynamics of amorphous polymer melts is still insufficient for understanding important polymer properties on a fundamental level. Here, advanced solid-state NMR spectroscopy provides a powerful probe for investigating the segmental and translational chain dynamics of molten poly(ethyl-methacrylates) (PEMA).

50 degrees above the glass transition, a lineshape corresponding to an axially symmetric chemical shift tensor is observed in ¹³C spectra for the carboxyl carbon. This occurs on account of the local β-process becoming fast on the NMR time scale. Further line narrowing with increasing temperature is attributed to a randomization due to translational chain motion. Assuming a random jump model, line shape analysis leads to correlation times for the chain motion, which are in good agreement with those determined by alternative NMR techniques. For longer time scales, the translational dynamics in the melt leads to a complete loss of correlation and therefore yields an isotropic 2D exchange pattern. A typical length scale for the local ordering in PEMA can be estimated by small-angle X-ray measurements.