Rheological study of a high-performance polyimide. Interpretation of the secondary mechanical relaxations of a nadimide crosslinked system

Thanks to the study of model compounds, we have been able to determine the origin of three rheological transitions observed in the thermomechanical analysis of a crosslinked nadimide resin, in the thermal range (-150 degrees C-400 degrees C). The first one, localized at about 300 degrees C, is attributable to the glass transition of the crosslinked compound. The two others (called gamma and beta) are respectively situated at -100 degrees C and 70 degrees C. They are due to localized motions of rigid segments comprising aromatic structures and imide rings.