Highly tough, colorless, transparent polyamide-imide films from one reaction vessel without purification

Polyamide-imide varnishes and films were prepared from one reaction vessel through a continuous process of amidation, chemical imidization, and acid removal reactions using commercially available aromatic monomers. The acid by-products generated from the amidation and chemical imidization were effectively removed using propylene oxide as a reactive additive. The varnishes had viscosities of 2300–2400 cP at 10wt% concentration in N, N-dimethylacetamide. The solubility parameters of the polymers were determined to be 23–24 MPa^1/2, which are very close to that of the solvent, and their fractional free volumes were determined to be 0.20–0.21, which are quite large as expected for common amorphous polymers. The polymer films showed extremely high mechanical strength (elastic moduli of up to 7.0 GPa and tensile strength of up to 134 MPa) and thermodynamic stability (glass transition temperature of up to 370 °C) as well as excellent optical transparency (transmittance at 440 nm: > 88%) and low yellow index (< 2.0). Graphical abstract: Polyamideimides were prepared from one reaction vessel through a continuous process of amidation, chemical imidization, and acid removal reactions without purification. The polymer film showed extremely high elastic moduli of up to 7.0 GPa and tensile strength of up to 134 MPa depending on the content of amide bond while its glass transition temperature reached up to 370 °C and its optical transmittance and yellow index reached > 88% and < 2.0, respectively.[Figure not available: see fulltext.].