Characterization of penetrant interactions in Kapton polyimide using a gravimetric sorption technique

Sorption of pure anhydrous ammonia and pure sulfur dioxide in Kapton polymide has been measured at 30 and 35°C at subatmospheric pressures using a McBain quartz spring balance. The sulfur dioxide sorption and desorption was well described by the Fickian transport model; however, the ammonia sorption exhibited significant deviations from Fickian behavior. A substantial fraction of the initially sorbed ammonia remained in the film after extended periods under vacuum at 35°C. Infrared analysis of the treated film revealed the presence of new carbonyl and nitrogen–hydrogen stretching peaks characteristic of primary and secondary amides. These observations suggest that the ammonia reacts chemically with some of the imide linkages. Based on infrared analysis of the ammonia‐exposed Kapton, heating the sample under vacuum at 120°C caused re‐formation of most of the orginally disturbed imide structures, with attendant evolution of ammonia as a condensation product.