Early in its polyimide insoluble in organic solvents, as one of the characteristics. For example, pyromellitic dianhydride and diamine polyimide ether can be dissolved in concentrated sulfuric acid, fuming nitric acid, or a mixture of SbCl3 SbCl3 and ASCl3 in, insoluble in organic solvents. With the development of technology, for there can be dissolved in an organic solvent requirements polyimide more urgent. This also contributed to the study of soluble polyimide. Ways to improve the basic polyimide solubility are two: one is the introduction of the solvent having an affinity for structures, such as the introduction of fluorine, silicon or phosphorus group. Another is to make the structure of the polymer becomes loose, such as the introduction of bridging groups, pendant, ring, can also be used on non-symmetrical structure of the monomer or copolymer macromolecular chains disrupted order and symmetry . In fact, the introduction of fluorine, silicon or phosphorus groups typically also have to make the structure of the polymer becomes loose action. In particular introduction hexafluoropropyl. It should be noted that the solubility of the polyimide and its synthesis method, in particular has a lot to cyclization process. Typically, compared with a thermal chemical cyclization to give the cyclized polyimide has good solubility. This is in addition to high due to the heat caused by the molecular chain orientation. Even crystallized, the high temperatures may also lead to cross-linked polymers. As a wholly aromatic, non-substituted polyimide, the most commonly used solvents are phenols, such as phenol, m-cresol and p-chloro-phenol. For example, containing ether or thioether dianhydride can be synthesized polyimide was dissolved in phenol and cresol. Biphenyl ether dianhydride and diamine or p-phenylene diamine polyimide can be dissolved in p-chlorophenol. The fluorine-containing polyimide dissolved in a more polar aprotic solvents, and even some of the common low-boiling solvent. Such as tetrahydrofuran, a halogenated hydrocarbon, or ketone solvents. Such as acetone, cyclohexanone, methyl ethyl ketone or the like. Polyimide and other pyridine base is unstable, especially at high temperatures, and therefore can not be practically used as a solvent for the polyimide. Some solvents can dissolve the polyimide having effect against, respectively, i.e., two kinds of solvents can dissolve the polyimide, but the mixture is no longer soluble.