DIELECTRIC-RELAXATION OF POLYDIMETHYLSILOXANE

In the reported experiments, dielectric studies were performed on crystallized and amorphous polydimethylsiloxane which had been characterized by differential thermal analysis and polarized light microscopy. The crystallized specimen displayed one relaxation near 160 K at 1 kHz while the amorphous specimen showed absorption peaks at 155 and 165 K. For the latter material the high-temperature peak was not due to a true relaxation but resulted from crystal nucleation at 160 K and the subsequent growth of spherulites. The low-temperature peak at 155 K resulted from the relaxation associated with the glass transition. A sharp decrease of dielectric constant was observed for both specimens at the melting point (235 K). For the dielectric relaxation associated with the glass transition in crystallized specimens, the values of the dispersion amplitude, the apparent activation energy at 160 K, and the half-width of the absorption curve are 0. 43 and 29 kcal/mole, and 5. 6 decades, respectively, which are in marked contrast to the corresponding values of 0. 82, 18, and 2. 2 for amorphous specimens.