TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: Diamine-based monomer includes 10-40 mole% TCHD and 60-90 mole% TFDB. Diamine-based monomer further includes bis-aminohydroxyphenyl hexafluoropropane (DBOH), bis-aminophenoxybenzene (1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene or 1,4-bis(4-aminophenoxy)benzene), bis-aminophenyl hexafluoropropane (33-6F, 44-6F), bis-aminophenyl sulfone (4,4'-diaminodiphenyl sulfone or bis(3-aminophenyl)sulfone), bis-aminophenoxyphenyl hexafluoropropane (4BDAF), bis-aminophenoxyphenyl propane (6HMDA) or bis-aminophenoxydiphenyl sulfone (DBSDA). Dianhydride-based monomer includes 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, cyclobutane tetracarboxylic dianhydride (both preferred), biphenyltetracarboxylic dianhydride, bicyclo(2.2.2)oct-7-ene 2,3,5,6-tetracarboxylic dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, bis-carboxyphenyl dimethylsilane dianhydride, oxydiphthalic dianhydride, bis-dicarboxyphenoxy diphenylsulfide dianhydride, sulfonyl diphthalic anhydride or isopropylidene-bis phenoxy phthalic anhydride. The amount of 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride, cyclobutane tetracarboxylic dianhydride in dianhydride-based monomer includes 20-100 mole%, where the molar ratio of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, cyclobutane tetracarboxylic dianhydride is 1-5:1.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The birefringence index of the polyimide film is less than 0.008. The surface direction phase difference (Ro) is less than 1 nm, and the thickness direction phase difference (Rth) is less than 100 nm (having a thickness of 10-12 mu m). The permeability is more than 88% based on the film thickness (10-12 mu m) when measured using a UV spectrometer at 550 nm. The coefficient of thermal expansion at 50-300 degrees C is less than 40 parts per million/ degrees C. EXAMPLE - Nitrogen was passed in a 1 l reactor, filled with 572.6 g N,N-dimethylacetamide to adjust the temperature of the reactor at 60 degrees C, and then dissolved with 3.43 g (0.03mol) trans 1,4-diamino cyclohexane and 38.43 g (0.12mol) bis-trifluoromethyl benzidine. The obtained solution was cooled to 25 degrees C, and reacted with 53.31 g (0.12mol) 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride and 5.88 g (0.03mol) cyclobutane tetracarboxylic dianhydride at 25 degrees C for 1 hour to obtain polyamic acid solution having a solid content of 15 wt.% and 475 poise viscosity. The obtained polyamic acid solution was applied on a stainless steel plate as 90 mu m cast, subjected to hot-air drying at 150 degrees C for 1 hour, 200 degrees C for 1 hour and 300 degrees C for 30 minutes, cooled and separated from plate to obtain 12 mu m polyimide film.