Two aromatic polyimides and the corresponding precursors (polyamic acid), with oxadiazole andpara/meta phenoxyphenylene rings in the main chain, were synthesised and the structure - thermalproperties correlation was followed by dynamic mechanical analysis. Only for the poly(amic acid) withmeta-oriented rings, more flexible than that para-oriented ones, it was possible to emphasize partiallythe glass transition domain because the imidization reaction takes place with increasing temperature.Over 200oC the thermogram starts to monitor the characteristics for the emerging polyimide. Afrequency dependent experiment was performed to calculate the activation energy of the transitionlocalized under 200oC to establish its nature. Consecutive heating – cooling - heating cycles wereaccomplished with the aim to distinguish between the imidization process and α - transitions. Moreover,information on how the imidization process gets forward were obtained. The polymer chain loosesgradually the flexibility and the glass transition temperature corresponding to the residual poly(amicacid) shifts to higher temperature. All phenomena are discussed by deep cross-examination of thestorage modulus (E’), loss modulus (E’’) and loss factor tan δ variation with temperature.
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