PI synthesis process and route: two-step method is commonly used

The synthesis methods of polyimide(PI) are mainly divided into one step, two step and three step. Among them, the two-step method is the common synthesis method, and the three-step method is relatively new and gradually attracted attention.

One-step method: the earliest synthesis method, the choice of reaction solvent is the key. The one-step method is the direct polymerization of dianhydride and diamine in a high boiling point solvent to produce PI, that is, the monomer does not go through the polyamide acid and the direct synthesis of PI. The reaction conditions of this method are milder than that of heat treatment, and the key is to choose the appropriate solvent. Two-step method: Now commonly used synthesis method, chemical imide method is the core technology. I

n the two-step process, the precursor polyamide acid is obtained from dianhydride and diamine, and then polyimide is formed by heating or chemical method, and the intramolecular dehydration is closed loop. 1. The thermal method is to heat the polyamide acid, dehydrate it and imide it in a closed loop to make a film. 2. Chemical iminization method is to add a certain amount of dehydrating agent and catalyst in the polyamide acid solution with the temperature kept below -5 ° C, quickly mix and evenly, and heat to a certain temperature to dehydrate the closed-loop iminization and make a film. In the manufacture of polyimide film, compared with chemical imide method, thermal imide process and equipment is simpler. Usually, the chemical imide method has a high production capacity and the obtained film has good physical and chemical properties, but almost all manufacturers in China use the thermal imide method. The two-step process is mature, but the polyamide acid solution is unstable and sensitive to water vapor, and often decomposes during storage. Three-step method: Novel synthesis methods that are gaining attention.

The three-step method is stable by polyisimide structure, as the precursor of polyimide, due to the heat treatment will not release water and other low molecular substances, easy to isomerize imide, can produce excellent performance of polyimide. This method is relatively new and is receiving wide attention. The coating methods of PI film can be divided into dipping method, casting method and bidirectional drawing method according to the different processes. The film prepared by bidirectional tensile method has the best performance, and the process is difficult and has high technical barriers.