Patent ID: 8846852

Claim:
A polyimide film obtained from an imide of polyamic acid, said polyamic acid being obtained by polymerizing diamines and acid dianhydrides, wherein an absolute molecular weight is 30,000 to 170,000, and the absolute molecular weight is determined by the following Formula 1: R θ K * ⁢ c = MP ⁡ ( θ ) - 2 ⁢ A 2 ⁢ cM 2 ⁢ P 2 ⁡ ( θ ) Formula ⁢ ⁢ 1 wherein, R θ is the excess Rayleigh ratio; K*=4π 2 n 0 2 (dn/dc) 2 λ 0 −4 N A −1 , wherein n 0 is a refractive index of solvent, N A is Avogadro's number, and dn/dc is a specific refractive index increment, that is differentiated from a change rate of refractive index changed according to a change rate of concentration of dilute solution and is determined within the range of 0.001 to 0.1 g/ml as a concentration change section, when a refractive index is detected by injecting a polyimide film in a state of dilute solution in an organic solvent into a flow cell of differential refractometer; c is a polymer concentration (g/ml) in a solution; M is molar mass, and weight average molecular weight (Mw) in the case of polydisperse sample; A 2 is the second virial coefficient; and P(θ)=R θ /R 0 , wherein said acid dianhydrides comprise (i) 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, and (ii) at least one selected from the group consisting of 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, 4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride), pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, and oxyphthalic dianhydride; 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride is introduced to a polymerization mixture last in the order of introducing the acid dianhydrides; and wherein the polyimide film is obtained by further heating after making film.