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 °C and glass transition in the range of 165–183 °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® 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®. The dielectric spectroscopy data corroborated with the dynamo-mechanical analysis ones showed distinct sub-glass transitions for these polymers: γ relaxations with activation energies of 44 and 45 kJ/mol, and a β relaxation with an activation energy of 107 kJ/mol. The dielectric properties are discussed in comparison with those of Kapton HN® film measured under the same conditions.

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