Dielectric and Other Properties of Polyimides in Relation to Water Content.

Polyimide films containing up to 3.2 wt % water (H_2O or D_2O) have been studied by dielectric relaxation, diffusion and ^2H NMR spectroscopy. The results of these measurements on thick (>=q50 μm) films reveal the presence of two distinct regions where the water molecules reside, an inner layer and an outer region. There is no evidence of microscopic voids containing isotropically free water, nor is there any indication of strongly bound water molecules. The water appears to be distributed homogeneously throughout the outer layer and somewhat clustered in the inner region as suggested by diffusion and NMR spin-spin relaxation results. Additional measurements on polyimides containing methanol and acetic acid absorbents are also presented.