The reaction between adipic acid and hexamethylenediamine in the synthesis of nylon-6,6 is a condensation polymerization reaction. The mechanism involves the formation of an amide bond between the carboxylic acid group of adipic acid and the amine group of hexamethylenediamine, with the elimination of a water molecule. The process is repeated multiple times, leading to the formation of a long-chain polymer known as nylon-6,6.The mechanism can be described in the following steps:1. Nucleophilic attack: The lone pair of electrons on the nitrogen atom of the amine group in hexamethylenediamine attacks the carbonyl carbon of the carboxylic acid group in adipic acid.2. Proton transfer: A proton from the amine group is transferred to the oxygen atom of the carboxylic acid group, forming an intermediate.3. Elimination of water: The intermediate collapses, releasing a water molecule and forming an amide bond between the two monomers.4. Chain growth: The process is repeated with more adipic acid and hexamethylenediamine molecules, leading to the formation of a long-chain polymer nylon-6,6 .For the reaction to occur efficiently, specific conditions are required:1. Temperature: The reaction is typically carried out at elevated temperatures, around 200-300C, to facilitate the formation of the amide bond and promote the elimination of water.2. Catalyst: A catalyst, such as phosphoric acid, is often used to increase the reaction rate and improve the yield of nylon-6,6.3. Pressure: The reaction is performed under high pressure to ensure that the monomers are in close proximity, which promotes the formation of the polymer.4. Removal of water: As the reaction is reversible, it is essential to continuously remove the water produced during the reaction. This can be achieved by using a Dean-Stark apparatus or by carrying out the reaction under a nitrogen atmosphere to prevent the reverse reaction hydrolysis from occurring.5. Purification: After the reaction is complete, the nylon-6,6 polymer is purified by washing with water to remove any unreacted monomers and catalysts. The purified polymer is then dried and processed into fibers or other forms for various applications.