The optimal stoichiometric ratio of adipic acid and hexamethylenediamine for the synthesis of nylon-6,6 is 1:1. This is because one molecule of adipic acid reacts with one molecule of hexamethylenediamine to form one molecule of nylon-6,6 and two molecules of water.Adipic acid: HOOC- CH2 4-COOHHexamethylenediamine: H2N- CH2 6-NH2The reaction can be represented as:HOOC- CH2 4-COOH + H2N- CH2 6-NH2 [-OC- CH2 4-COO- CH2 6-NH-]n + 2nH2OVarying the stoichiometric ratio of adipic acid and hexamethylenediamine can affect the yield and properties of the final product. If there is an excess of one reactant, the reaction will not go to completion, and the yield of nylon-6,6 will be reduced. In addition, the presence of unreacted starting materials can lead to impurities in the final product, which can affect its properties such as mechanical strength, thermal stability, and chemical resistance.To obtain the highest yield and best properties of nylon-6,6, it is essential to maintain a 1:1 stoichiometric ratio of adipic acid and hexamethylenediamine during the synthesis process.