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X-Ray Diffraction Study of Polyimide Blends Compatibility

An X-ray diffractometry method has been employed to investigate the compatibility characteristics of two polyimide blend systems. From the in-plane and out-of-plane X-ray diffraction patterns, it is learned that the higher in chain rigidity, the higher ordering and film orientation can one observe in the on-substrate cured polyimide films. By comparing the out-of-plane diffraction patterns from the stacked films of the blends, laminates, random copolymers, and alternating copolymers, it can be concluded that the blends of PMDA-ODA/PMDA-PDA (pyromellitic dianhydride-oxydianiline/pyromellitic dianhydride-p-phenylenediamine) are compatible at all compositions except at above 90% PMDA-PDA. The blends of PMDA-ODA/PMDA-B (pyromellitic dianhydride-benzidine) are not compatible. Kept mixed longer, the characteristic diffraction peak intensities of the blends with PMDA-B composition less than 50% have decreased and become undistinguishable from those of the corresponding random copolymers, and those with higher PMDA-B composition have also decreased significantly. It is plausible to say that the blends with diffraction patterns undistinguishable from those of the corresponding random copolymers have actually converted to random copolymers due to exchange reactions occurred among the amic acid compounds when in the solution state.