US Patent 11603440 Polyimide films and electronic devices

In a first aspect, a polyimide film includes a dianhydride and a diamine. The dianhydride, the diamine or both the dianhydride and the diamine include an alicyclic monomer, an aliphatic monomer or both an alicyclic monomer and an aliphatic monomer. The polyimide film has a b* of 1.25 or less and a yellowness index of 2.25 or less for a film thickness of 50 μm. The polyimide film is formed by: (a) polymerizing the dianhydride and the diamine in the presence of a first solvent to obtain a polyamic acid solution; (b) imidizing the polyamic acid solution to form a substantially imidized solution; (c) casting the substantially imidized solution to form a film; and (d) drying the film.