TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The organic solvent is dimethylformamide, dimethylacetamide, N-methylpyrrolidone, m-cresol, tetrahydrofuran and/or chloroform.    TECHNOLOGY FOCUS - POLYMERS - Preferred Method: (III) is obtained by polymerizing 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl. The polyimide film is formed by a copolymer that is obtained by 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 3,3',4,4'-biphenyltetraamine. The content of 3,3',4,4'-biphenyltetraamine in the polyimide film relative to 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride content is 0.1-10 mole%. The copolymerization reaction is performed under inert atmosphere at -10 to 60 degrees C for 1-24 hours. The imidization is performed by thermal imidization or chemical imidization method or by both methods. Preferred Components: The polyimide film has thickness of less than or equal to 100 mu m, transmittance of more than 80%, a yellow index of less than 3, b value of less than 2, a storage modulus at 50 degrees C of more than 1.8 GPa and a glass transition temperature (Tg) of more than 330 degrees C. Preferred Definitions:    R = biphenyl, diphenyl ether, diphenyl ketone or diphenyl sulfone moiety.    EXAMPLE - 51.2 g 2,2'-Bis(trifluoromethyl)-4,4'-diaminobiphenyl and 0.034 g 3,3',4,4'-biphenyltetraamine were dissolved in 489.7 g dimethylformamide under nitrogen atmosphere at 10 degrees C. Then 71.2 g 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride was added to the obtained solution and reacted for 24 hours at 10 degrees C and polyamic acid solution was obtained. To the solution of polyamic acid, 20.6 g isoquinoline and 49 g acetic anhydride were added and stirred at 60 degrees C for 3 hours and polyimide solution was prepared. The polyimide solution was precipitated in 5 times weight ethanol and polyimide solid was obtained. The solid was filtered and dried at 90 degrees C for 24 hours and polyimide powder was obtained. The obtained polyimide powder was dissolved in 220 g dimethylformamide and 20 wt.% polyimide solution was obtained. Then the solution was heated to 80-300 degrees C at a heating speed of 2 degrees C/minute and the polyimide film with thickness of 40 mu m was formed.