Poly(amic diethyl ester) [PAE] precursors of four different polyimides with various chain rigidities were synthesized and thermally converted to the polyimides in thin films: rodlike poly(p-phenylene pyromellitimide) [PMDA- PDA] and poly(4,4'-biphenylene pyromellitimide) [PMDA-BZ], pseudo-rodlike poly(p-phenylene biphenylenetetracarboximide) [BPDA-PDA] and semiflexible poly(4,4-oxydiphenylene pyromellitimide) [PMDA-ODA PAE]. For the polyimide films, water sorption behaviors were investigated by gravimetry and then compared with those of the polyimides prepared from the corresponding poly(amic acid) [PAA] precursors. In addition, their morphological structures were examined by X-ray diffraction. For all the polyimides, both water sorption and morphological structure were dependent upon the history of precursor origin. All the polyimides except PMDA-ODA revealed relatively higher diffusion coefficient of water, higher water sorption, lower intermolecular packing order and lower population of a more ordered phase in the PAE-derived polyimide films than the corresponding PAA-derived polyimide films. For PMDA-ODA, the variations in the water diffusion and sorption due to the precursor origin were relatively small in spite of a relatively large change in the morphological structure. Overall, the effect of precursor origin on the water diffusion and sorption is significantly high in the rodlike or pseudo-rodlike polyimides having a high chain rigidity and high intermolecular packing order, but relatively low in the semiflexible polyimide with a relatively low chain rigidity. In comparison, regardless of the precursor origins, the diffusion coefficient of water was in the decreasing order PMDA-ODA > PMDA-PDA > PMDA-BZ > BPDA-PDA and, however, the water sorption was in the decreasing order PMDA-PDA > PMDA-BZ > PMDA-ODA > BPDA-PDA. These water diffusion and sorption behaviors were understood by considering their chemical affinities to water in addition to the morphological structures. (C) 1999 Elsevier Science Ltd.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Materials Chemistry