Abstract
Wholly aromatic polyamide-hydrazides (PAHs) are one of the most important classes of high-performance organic polymers due to their very high thermal and thermo-oxidative stabilities and exceptionally high mechanical resistance. These properties originate from their chemical structures, which are composed of aromatic nuclei, amide, and hydrazide linkages, which create the rigid rod-like macromolecular chains that allow for the establishment of strong intermolecular hydrogen bonds. These bonds create an effective crystallinity and high packing efficiency. Most of the wholly aromatic PAHs are soluble in dimethyl sulfoxide (DMSO), which can be used for spinning. Wholly aromatic PAHs do not have true melting points. These transitions are obscured by the cyclodehydration reaction that results in polyamide-1,3,4-oxadiazoles. Monsanto X-500 class of fibers, derived from poly[4-(terephthaloylamino)benzoic acid hydrazide], have a very high strength and ultra-high modulus, superior to glass fiber and steel wire. They can be successfully applied in fabrics, rigid composites, tire-cord, and impact-absorbing devices such as for single-use aircraft arresters and safety harnesses and also for ballistic protection. Wholly aromatic PAH films are used as reverse-osmosis membranes for water pollution control and for the concentration of fruit juices and as semipermeable membranes for the desalination of artificial and natural seawater. Wholly aromatic PAH-multiwalled carbon nanotube composites and modified wholly aromatic PAH--transition metal chelates are good semiconductors for electricity.