Polyesterdiimide prepolymers containing synthesized diimide-diacid monomer (DIDAn) were synthesized under conditions previously reported. One-component varnishes were obtained by mixing the synthesized prepolymers with phenol-blocked toluene diisocyanate (TDI) and/or hexamethylene diisocyanate (HMDI). The solubility parameter of diimide-modified polyester prepolymer was investigated using an intrinsic viscosity measurement. Thermal behavior and pyrolysis activation energy were also investigated using thermogravimetric analysis. The thermal stability increased with an increase in the content of DIDA. The diimide-modified polyester one-component varnishes coated onto an aluminum panel were found to be acceptable, according to the specification of ASTM D-3794.