Processable Aromatic Polyimides

This review article deals with aromatic polyimides that are processable from the melt or soluble in organic solvents. Conventional aromatic polyimides represent the most important family of heat resistant polymers, but they cannot be processed in the melt, and their application in the state of soluble intermediates always involves a hazardous step of cyclo-dehydration and elimination of a non-volatile polar solvent. A major effort has therefore been devoted to the development of novel soluble and/or melt-processable aromatic polyimides that can be applied in the state of full imidation. The structural factors conducive to better solubility and tractability are discussed, and representative examples of monomers showing favourable structural elements have been gathered and listed with the chemical criteria. Experimental and commercial aromatic polyimides are studied and evaluated by their solubility, transition temperatures and thermal resistance. An example is also given of the methods of computational chemistry applied to the study and design of polyimides with improved processability.