Photodegradation of Aromatic Polyimides

The photolysis results for a soluble polyimide, 6F-ODA, based on 2,2- bis(3',4'-dicarboxyphenyl) hexafluoropropane dianhydride (6F) and 4,4'- oxydianiline (ODA) were compared to the polyimides, PMDA-ODA and BTDA-ODA, based on, pyromellitic dianhydride (PMDA) and 3,3'4,4'-benzophenone tetracarboxylic dianhydride (BTDA), which were reacted with ODA. All the photolyses involved the exposure of thin polymeric films to a medium pressure mercury lamp (unfiltered) in air. The IR, UV, and weight loss results for the polymers suggest that an ablative process occurs upon photolysis. The spectral and weight loss changes were much greater for 6F-ODA. Dilute solution viscometric and gel permeation chromatographic analyses of the pristine and photolyzed 6F-ODA points toward a very rapid and efficient chain scission process along the polymer backbone. The strength of the charge transfer (CT) interactions in the respective polymers may explain in part the greater UV stability observed for the PMDA-ODA and BTDA-ODA.