Polyesterimide resin composition, polyesterimide resin layer, flexible metal foil laminate, and methods of preparing the same

A method of preparing a polyesterimide resin composition, the method comprising:

• preparing a polyamic acid through a reaction between a diamine and a dianhydride;
• and
• thermally or chemically converting the polyamic acid,
• wherein the polyesterimide resin composition comprises a compound having a structural unit represented by Chemical Formula 1:
• wherein, in Chemical Formula 1,
• m and n are mole fractions,
• “m+n=1”, “0.2≤m≤0.8”, and “0.2≤n≤0.8” are satisfied,
• Ar1 and Ar2 are the same as or different from each other and are each independently a tetravalent organic group having at least one aromatic ring,
• R1, R2, and R4 to R6 each independently comprise at least one selected from a group consisting of —H, —F, —CH3, —OCH3, —CF3, and —OCF3, and
• R3 is an ester group and comprises —COO— or —OOC—, and
• wherein the diamine comprises at least one selected from a group consisting of 4,4′-diamino-3,3′-dimethylbiphenyl (o-tolidine, CAS No. 119-93-7), 4,4′-diamino-2,2′-dimethylbiphenyl (m-tolidine, CAS No. 84-67-3), 2,2′-bis(trifluoromethyl)benzidine (22TFMB, CAS No. 341-58-2), 3,3′-bis(trifluoromethyl)benzidine (33TFMB, CAS No. 346-88-3), 1,4-phenylene-di-4-aminobenzoate (ABHQ, CAS No. 22095-98-3), and bis(4-aminophenyl)terephthalate (BPTP, CAS No. 16926-73-1).

A method of preparing a polyesterimide film, the method comprising:

• applying a polyamic acid-based resin composition convertible into a polyesterimide resin onto a metal belt;
• forming a gel film by thermally or chemically imidizing the polyamic acid-based resin composition;
• and
• separating the gel film from the metal belt.