Aqueous degradation of polyimides

Abstract

The effect of an aqueous environment on the tensile properties of Kapton polyimide film has been investigated. Immersion of specimens in distilled water at 25° to 100°C for time periods ranging from one hour to several hundred hours resulted in a decrease in the ultimate tensile strength of the polymer from 23 ksi to approximately 14 ksi, and a corresponding decrease in elongation to failure from 38% to approximately 5%. The kinetics of this decrease in mechanical properties are second order and yield an activation energy of approximately 15.6 kcal/mole. The reaction is slightly dependent on pH in the range 2.0 to 12.0, but is highly dependent on the pH in the range 0.4 to 2.0. The decrease in mechanical properties at pH 2.0 to 6.0 appears to be due to hydrolysis of either uncyclized amic acid linkages or diamide functional groups present in the polyimide, whereas that at pH below 2.0 is probably the result of hydrolysis of both imide and amide bonds. Prolonged reflux of the polyimide in water resulted in the extraction of a water‐soluble, amide‐containing material.