Nylon -66 can be obtained by polycondensation of adipic acid and hexamethylene diamine. In industry, in order to react adipic acid and hexamethylenediamine with equal molar ratio, nylon -66 salt is generally made first, and then polycondensation is carried out. When water comes out, amide bonds are formed and linear polymers are formed. Therefore, the diffusion speed of water in the system determines the reaction speed, so it is the key to discharge water from the reaction system efficiently in a short time. The polycondensation process can be carried out continuously or intermittently.

There are side reactions such as macromolecular hydrolysis, amine hydrolysis (when there is too much amine), acid hydrolysis (when there is too much acid) and high temperature pyrolysis in the polycondensation process, which reduces the molecular weight of nylon 66.