\u2022 Adipic acid, the most important dicarboxylic acid from an industrial point of view: This white crystalline powder is produced annually at approximately 2.5 billion kilograms, mainly as a precursor for the production of nylon. Otherwise, adipic acid is rarely found in nature. About 60% of the 2.5 billion kg of adipic acid produced annually is used as a monomer for the manufacture of nylon by forming nylon 66 through a polycondensation reaction with hexamethylenediamine. . Other major uses also include polymers. It is a monomer used to make polyurethane and its ester is a plasticizer.