| 摘要 |
PROBLEM TO BE SOLVED: To obtain a polyimide having a constant loss of optical transmission by reacting a tetracarboxylic acid dianhydride having a specified or higher purity with a diamine having a specified or higher purity. SOLUTION: A tetracarboxylic acid dianhydride (e.g. pyromellitic dianhydride or (trifluoromethyl)pyromellitic dianhydride) having a purity of 95% or higher and diaminodiphenyl ether or 2,2'-bis(trifluoromethyl)-4,4'-diaminoethyl having a purity of 95% or higher, at least either of which must be a fluoro compound, are dissolved in a diamine/tetracarboxylic acid molar ratio of 1/(0.95-1.05) in a polar solvent such as N,N-dimethylacetamide. Next, the solution is subjected to a reaction at 0-50 deg.C to produce a solution of a polyimide precursor having a weight average molecular weight of 10,000-1,000,000. This solution is applied to an optical substrate such as made of glass, and the wet film is heated to 150-400 deg.C to effect closure into imide rings, dried and cured to obtain a polyimide film. |
