Confirmation of the presence of imine bonds in thermally cured polyimides

Model compounds for imines formed during the thermal curing of short chain polyimides have been synthesized and characterized. These compounds have imine bonds (CN) formed by the nucleophilic attack of primary amines on imide carbonyls. The CN stretching mode appears at 1649–1664 cm−1 in the Raman and infrared spectra of these compounds and the band assigned to the carbonyl mode in an imide ring with an imine bond appears near 1740 cm−1. These compounds have been prepared and characterized to verify the conclusions of a previously reported study in which bands observed in thermally cured short chain polyimides at 1656 and 1742 cm−1 were assigned as the CN and associated CO modes, respectively. It has also been confirmed that the CN stretching mode in the imide model compounds is inherently IR weak and can only be seen if the concentration of imine species is high. © 1993 John Wiley & Sons, Inc.