The synthesis of nylon-6,6 from adipic acid and hexamethylenediamine involves a condensation polymerization reaction. Here's the step-by-step mechanism for this reaction:1. Activation of the carboxylic acid group: Adipic acid, which is a dicarboxylic acid, has two carboxylic acid groups -COOH that can react with the amine groups -NH2 of hexamethylenediamine. The first step in the reaction is the activation of one of the carboxylic acid groups in adipic acid. This is typically done by converting the carboxylic acid group into a more reactive species, such as an acyl chloride -COCl or an ester -COOR . This can be achieved by treating adipic acid with thionyl chloride SOCl2 or an alcohol ROH in the presence of a catalyst.2. Nucleophilic attack by the amine group: Once the carboxylic acid group is activated, the amine group of hexamethylenediamine can attack the carbonyl carbon, forming a tetrahedral intermediate.3. Proton transfer and elimination of the leaving group: The tetrahedral intermediate collapses, transferring a proton to the oxygen atom and eliminating the leaving group either chloride ion or an alkoxide ion . This forms an amide bond between the adipic acid and hexamethylenediamine molecules.4. Chain propagation: Steps 2 and 3 are repeated, with the remaining carboxylic acid group in the adipic acid molecule reacting with another hexamethylenediamine molecule, and the remaining amine group in the hexamethylenediamine molecule reacting with another adipic acid molecule. This process continues, forming a long chain of alternating adipic acid and hexamethylenediamine units, which is nylon-6,6.Changing the reaction conditions can affect the yield and properties of the resulting nylon-6,6 polymer:1. Temperature: Increasing the reaction temperature can increase the rate of the reaction, leading to a higher yield of nylon-6,6. However, excessively high temperatures can cause side reactions or degradation of the polymer, resulting in lower molecular weight and inferior properties.2. Catalysts: The use of catalysts can increase the rate of the reaction and improve the yield of nylon-6,6. Common catalysts for this reaction include tertiary amines and metal salts.3. Solvents: The choice of solvent can affect the reaction rate and the properties of the resulting nylon-6,6. Polar aprotic solvents, such as dimethylformamide DMF or dimethyl sulfoxide DMSO , are often used in this reaction to dissolve the reactants and facilitate the reaction.4. Reaction time: Longer reaction times can lead to higher molecular weight polymers, which can improve the mechanical properties of the resulting nylon-6,6. However, excessively long reaction times can also lead to side reactions or degradation of the polymer.5. Monomer ratio: The stoichiometric ratio of adipic acid to hexamethylenediamine should be 1:1 for the formation of nylon-6,6. Deviations from this ratio can result in incomplete polymerization and lower molecular weight polymers.By carefully controlling these reaction conditions, it is possible to optimize the yield and properties of the resulting nylon-6,6 polymer for specific applications.