TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The solvent is greater than or equal to 2C alkyl substituted tert-amine, preferably N,N-diethylacetamide and/or N,N-diethylformamide.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The polyimide is of formula (II). The solid content of the solution is 10-25 wt.%. The solution has viscosity of 2000-10000 centipoise at 25 degrees C when measure using Brookfield rotational viscometer. The weight-average molecular weight of the polyimide is greater than or equal to 40000. The glass transition temperature of the polyimide is greater than or equal to 250 degrees C. The polyimide film has light transmittance of greater than or equal to 85% at 380-760 nm and film thickness of 10-30 mu m, yellowness (YI) of less than 8, modulus of greater than or equal to 1.5 Gpa, coefficient of thermal expansion of less than or equal to 70 ppm/K at 280 degrees C, the maximum stress value of 40-120 MPa, the maximum elongation of 10-100%, the in-plane phase-difference (Rin) of 0.05-1 nm, and phase-difference value along the thickness direction (Rth) of less than or equal to 100 nm.p, q, r = number of repeating units, where p+q+r is equal to 1, p/(p+q+r) is 0.1-0.9, preferably 0.3-0.7, q/(p+q+r) is 0.1-0.9, and r/(p+q+r) is 0-0.8;X1-X3 = aromatic tetravalent organic group having fluoro substituent, preferably aromatic tetravalent organic group derived from 4,4'-(hexafluoroisopropylidene)diphthalic anhydride;Y11 = divalent organic group derived from aromatic diamine having fluoro substituent, preferably 2,2'-bis(trifluoromethyl)benzidine; andY2, Y3 = divalent organic group derived from aromatic diamine having no fluoro substituent, preferably p-phenylenediamine, m-phenylene diamine, 4,4-diaminodiphenyl ether or 4,4'-(9-fluorenylidene)dianiline. EXAMPLE - 15 g 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride was dissolved in 30 g diethylformamide for 20 minutes under nitrogen atmosphere. A solution prepared by mixing 5.4 g 2,2'-bis(trifluoromethyl)benzidine, 1.82 g m-pheylenediamine and 30 g diethylformamide was added to the obtained solution, heated to 40 degrees C and reacted for 24 hours. The viscosity of the obtained solution was adjusted to 5000 centipoise and the solid content was adjusted to 18 wt.% using diethylformamide. The obtained solutions was homogenized for 24 hours to obtain the polyimide solution.