Intercalation behavior of polyimide/organoclay nanocomposites during thermal imidization

To understand the intercalation behavior of polyimide (PI)/clay nanocomposites during thermal imidization, two different types of poly(amic acid) (PAA) were synthesized, and the corresponding hybrids with organically treated clays (O-MMT) were also prepared. The changes in molecular structure of the polymer matrix, interlayer spacing, and fracture morphology with a series of thermal imidization steps were investigated. The PAA/clay nanocomposites initially showed two X-ray diffraction peaks, indicating two levels of intercalation. As the temperature at which the thermal imidization step was performed increased, the peak intensity of the higher angle peak increased, and it remained as a unique peak at 2θ=6.70 (d-spacing of 13.2Å) for both PI(1), based on pyromellitic dianhydride (PMDA)+4,4′-oxydianiline (ODA), and PI(2), based on PMDA+4,4′-(9-fluorenylidene)-dianiline (9FDA). However, the lower angle peak became smaller and broader, and the angle became higher. This peak finally disappeared after thermal treatment at 300 °C for PI(1), but did not disappear completely for PI(2), although the peak showed a marked decrease in intensity and became broader.