TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The second solvent has a polarity lower than that of the first solvent. The first solvent comprises at least one of meta-cresol, N-methyl-2-pyrrolidone (NMP), dimethyl formamide (DMF), dimethyl acetamide (DMAc), dimethyl sulfoxide (DMSO), acetone, diethyl acetate; a low boiling point solvent; or a low absorbing solvent. The second solvent comprises at least one of water, alcohols, ethers or ketones. The aromatic dianhydride comprises at least one of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydro-naphthalene-1,2-dicarboxylic anhydride (TDA) or 4,4'-(4,4'-isopropylidene-diphenoxy)bis(phthalic anhydride) (HBDA), and at least one of pyromellitic dianhydride (PMDA), biphenyl tetracarboxylic dianhydride (BPDA) or oxy-diphthalic dianhydride (ODPA). The aromatic diamine comprises at least one of 2,2-bis(4-(4-aminophenoxy)-phenyl)propane (6HMDA), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (2,2'-TFDB), 3,3'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (3,3'-TFDB), 4,4'-bis(3-aminophenoxy)diphenylsulfone (DBSDA), bis(3-aminophenyl)sulfone (3DDS), bis(4-aminophenyl)sulfone (4DDS), 1,3-bis(3-aminophenoxy)benzene (APB-133), 1,4-bis(4-aminophenoxy)benzene (APB-134), 2,2'-bis(3(3-aminophenoxy)phenyl)hexafluoropropane (3-BDAF), 2,2'-bis(4(4-aminophenoxy)phenyl)hexafluoropropane (4-BDAF), 2,2'-bis(3-aminophenyl)hexafluoropropane (3,3'-6F), 2,2'-bis(4-aminophenyl)hexafluoropropane (4,4'-6F) and oxydianiline (ODA). EXAMPLE - While nitrogen was passed through a 100 ml three-neck round bottom flask reactor equipped with a stirrer, a nitrogen inlet, a dropping funnel, a temperature controller and a condenser, 31.82 g of N,N-dimethyl acetamide (DMAc) was placed in the reactor, the temperature of the reactor was decreased to 0 degrees C. 2,2'-Bis(trifluoromethyl)-4,4'-diaminobiphenyl (2,2'-TFDB) (3.2023 g) was dissolved in it, and then this solution was maintained at 0 degrees C. Further, 4.164 g of 4,4'-(4,4'-isopropylidene-diphenoxy)bis(phthalic anhydride) (6HBDA) was added to it and stirred for 1 hour thus completely dissolving the 6HBDA after which 0.58844 g of biphenyl tetracarboxylic dianhydride (BPDA) was added to it, thus completely dissolving the BPDA. The solid content was thus 20 wt%. The solution was then stirred at room temperature for 8 hours, thus obtaining a polyamic acid solution having a viscosity of 1900 cps at 23 degrees C. The polyamic acid solution thus obtained was added with 2-4 equivalents of each of acetic anhydride and pyridine and was then heated at a heating rate of 1-10 degrees C/minutes at 20-180 degrees C for 2-10 hours, thereby imidizing the polyamic acid solution. The imidized solution (30 g) was added to 300 g of water, after which the precipitated solid was filtered and milled thus obtaining powder, which was then dried in a vacuum oven at 80-100 degrees C for 2-6 hours, giving about 8 g of solid resin powder. The solid resin thus obtained was dissolved in 32 g of DMAc or DMF serving as a polymerization solvent, thus obtaining a 20 wt.% polyimide solution. The polyimide solution was heated at heating rate of 1-10 degrees C/minutes at 40-400 degrees C for 2-8 hours, resulting in polyimide films (test) having a thickness of 50-100 mu m. As in test example, 5.1846 g of 2,2'-bis(4(4-aminophenoxy)phenyl)hexafluoropropane (4-BDAF) was dissolved in 38.5084 g of DMAc, after which 4.4425 g of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) was added to it and stirred for 1 hour, thus completely dissolving the 6FDA. The solid content was thus 20 wt.%. The solution was then stirred at room temperature for 8 hours, thus obtaining a polyamic acid solution having a viscosity of 1300 cps at 23 degrees C. The polyamic acid solution obtained after the completion of the reaction was spread to a thickness of 500-1000 mu m on a glass substrate using a doctor blade, and was then dried in a vacuum oven at 40 degrees C for 1 hour and at 60 degrees C for 2 hours, thus obtaining a self-supporting film, which was then heated in a high-temperature oven at 80 degrees C for 3 hours, 100 degrees C for 1 hour, 200 degrees C for 1 hour, and 300 degrees C for 30 minutes at a heating rate of 5 degrees C/minutes, thereby affording polyimide films (control) having a thickness of 25 mu m, 50 mu m and 100 mu m. The test/control films were evaluated for 50% cut-off, coefficient of linear thermal expansion and yellowing index. The results for test/control films were: 50% cut-off (nm) = 392/411; coefficient of linear thermal expansion (ppm/ degrees C) = 33/52.3; and yellowing index = 1.35/9.7.