Polyimide, especially PMDA / ODA system can be used as material quickly enter one of the reasons the market, is a diamine and the dianhydride in an aprotic polar solvent in the polymerization of a polyamic acid prepolymer soluble. After heating the film from the polyamic acid imidization obtained insoluble polyimide. This solves the previously insoluble polymer in the heat-resistant polymer research often encountered, does not melt, difficult processing problems. However, generally an aprotic polar solvent having a higher boiling point. It is worth noting that these solvents can form molecular complexes with the polyamide acid. Even at very high temperatures nor can it be removed (it has been reported in at 300 ℃ can still find traces of residual solvent). This situation research and some applications difficult, which amount can reach 50% or even higher. Specific method is: the second solvent is mixed with DMF was added an equivalent amount of PMDA and ODA, stirring polymerization, the solid content of 15%. The second solvent may be gradually added to a stirred solution of polyamic acid in DMF, and stirring was continued until a homogeneous solution was obtained.
When mixed solvent is used in addition to the processing (e.g. coating) drying quickly, since the system still contains high-boiling polar solvent. Other circumstances (such as DMF to form complexes with the amide acid) is not much different when used alone DMF.