Synthesis route of polyimide

Polyimide has many varieties and forms, and there are many ways to synthesize it, so it can be selected according to various application purposes. This flexibility in synthesis is also difficult for other polymers to have. The synthesis is introduced as follows: Polyimide is mainly synthesized from dibasic anhydride and diamine. Compared with many other heterocyclic polymers, such as polybenzimidazole, polybenzothiazole, polyquinoline and other monomers, these two monomers have a wide source of raw materials and are easier to synthesize. There are many varieties of dianhydride and diamine, and different combinations can obtain polyimide with different properties.

Polyimide can be obtained by low-temperature polycondensation of dianhydride and diamine in polar solvents such as DMF, DMAC, NMP or THE/methanol mixed solvents to obtain soluble polyamic acid, which can be heated to about 300°C for dehydration and cyclization to convert into polyimide after film formation or spinning; acetic anhydride and tertiary amine catalysts can also be added to polyamic acid for chemical dehydration and cyclization to obtain polyimide solution and powder. Diamine and dianhydride can also be heated and polycondensed in high-boiling point solvents such as phenolic solvents to obtain polyimide in one step. In addition, polyimide can be obtained by the reaction of dibasic esters of tetrabasic acids and diamines; polyamic acid can also be converted into polyisoimide first and then into polyimide. These methods are convenient for processing. The former is called PMR method, which can obtain low-viscosity, high-solid solution, and has a window with low melt viscosity during processing, which is particularly suitable for the manufacture of composite materials; the latter increases solubility and does not release low molecular weight compounds during the conversion process.