Compression and Thermal Expansion Behaviors of Highly Crystalline Polyimide Particles Prepared from Poly(amic acid) and Monomer Salts

Characteristic changes in the structures and properties of polyimides induced by very high pressures up to 8 GPa

Various in situ measurement techniques have been applied to investigate changes in the three-dimensional structures and the properties of fully aromatic polymers (mainly aromatic polyimides: PIs) generated at very high pressures up to 8 GPa. In particular, significant changes occurred in the ordered structures, aggregation states, electronic structures, and intermolecular interactions in the repeating units of the PI molecular chains and were observed by applying pressure with a high-pressure optical cell (up to 0.4 GPa, ca. 4000 atm) or a diamond anvil cell (DAC, up to 8.0 GPa, ca. 80,000 atm). In addition, the structural changes in the PI molecular chain repeating units and interchain distances induced by the ultrahigh pressures were observed with wide-angle X-ray diffraction, and they were compared and contrasted with optical absorption, fluorescent and phosphorescent emission spectra, infrared absorption spectra, and refractive indexes observed under the same conditions. These findings obtained at very high pressures provide molecular design guidelines for new PI materials with novel optical, electronic, and thermal functionalities that are not easy to achieve under ambient conditions.