Dielectric relaxations in thermotropic liquid crystalline polypeptides

Thermally stimulated depolarization current (TSDC) and thermally stimulated polarization current (TSPC) measurements and the differential scanning calorimetry (DSC) method have been used for the investigation of thermal transitions in thermotropic poly( gamma -stearyl- alpha , L-glutamate). The beta peak (-80 degrees C) and alpha /sub 1/ and alpha '/sub 1/ peaks registered between -50 degrees C and 25 degrees C were attributed to movements of side chain dipoles. The alpha /sub 2/ peak, observed approximately=43 degrees C, was indicative of the melting of paraffinic side chains. The activation energies were determined for beta peaks and alpha /sub 2/ peaks at different heating rates. A good correlation between heating rate and the square of the maximum peak temperature was found, showing that these peaks are of dipolar origin. The alpha /sub 1/ and alpha /sub 2/ peaks were strongly influenced by thermal treatments. The position of alpha /sub 2/ was close to that determined by DSC. Depending on the thermal history of samples, the paraffinic side chain segments melted and crystallized over a large temperature range, suggesting the formation of crystallites with different dimensions.<
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