YOUNGS MODULUS AND SECONDARY MECHANICAL DISPERSIONS IN POLYPYROMELLITIMIDE

Dynamic mechanical properties were determined in polypyromellitimide at acoustic frequencies over a wide temperature range (80–750°K). Two distinct secondary relaxation effects were found: one (β′) at lower temperature, characterized by a loss maximum at 250°K, and another (β) at higher temperatures with a loss maximum at 400°K. The lower temperature peak is shifted towards higher temperature with increasing frequency following an Arrhenius‐type equation (apparent activation energy: 15 kcal/mole); the relaxation strength increases with water content and becomes practically zero when samples dried under vacuum at 200°C are examined. The β′ relaxation process is thus attributed to the presence of adsorbed water molecules. The higher‐temperature (β) dispersion, which persists even after dehydration, on the basis of some results obtained for other polymers containing p‐oxylphenylene rings in the backbone, is tentatively attributed to torsional oscillations of aromatic rings along the chain. Copyright © 1969 John Wiley & Sons, Inc.