Viscoelastic and dielectric behaviour of thin films made from siloxane-containing poly(oxadiazole-imide)s

Siloxane-containing poly(oxadiazole-imide)s were prepared by polycondensation reaction of two aromatic diamino-oxadiazoles with a dianhydride containing tetramethylsiloxane moiety. Free-standing flexible films having good mechanical properties were made therefrom. The polyimides exhibited high thermal stability with initial decomposition temperature being above 440 degrees C and glass transition in the range of 165-183 degrees C. The dielectric constant values, measured at room temperature and in the frequency domain of 1 Hz-1 MHz, are in the range of 2.69-2.90, being significantly lower in comparison with that of Kapton HN (R) film, whose dielectric constant values ranged from 3.13 to 3.24. The dielectric loss values are low, in the same range with those of Kapton HN (R). The dielectric spectroscopy data corroborated with the dynamo-mechanical analysis ones showed distinct sub-glass transitions for these polymers: gamma relaxations with activation energies of 44 and 45 kJ/mol, and beta relaxation with an activation energy of 107 kJ/mol. The dielectric properties are discussed in comparison with those of Kapton HN (R) film measured under the same conditions. (C) 2010 Elsevier Ltd. All rights reserved.