ABSTRACT
Jou and Huang investigated the behavior of blends of rod-like pyromellitic dianhydride-benzidine (PMDA-B) and semiflexible 6F-dianhydride-phenylendiamine polyimides (6FDA-PDA) with several different compositions. According to the results from x-ray diffractometry and Fourier transform infrared (FTIR) spectrometry, these two polyimides were incompatible when mixed at room temperature for 20 min. When mixed at 50°C for 40 h, the polymers, thermodynamically incompatible, became compatible owing to exchange reactions. Bending beam diffusion experiments showed that the diffusion of moisture in these films belongs to case I. The diffusion coefficient Dw was 10-10 cm2 / s in PMDA-B and 1.65 x 10-9 cm2 /s in 6FDA-PDA. In the blends, Dw increased with increasing content of 6FDA-PDA. The slow diffusion in PMDA-B was attributed to its highly crystalline structure and relatively small interchain spacing. The diffusion of
moisture was faster in the compatible films. Regardless of compatibility, diffusion in all the blends was much slower than in pure 6FDA-PDA. This was attributed to the comparatively small average interchain spacing of the blends (34).
