Mechanically Robust and Transparent Polyamideimide Films via Consecutive Polycondensation, Amidation, Acid Removal, and Bluing Agent Addition

Polyamideimides were prepared via consecutive high-temperature polycondensation imidization and amidation. The acid byproduct generated during amidation was removed using propylene oxide as a reactive additive, avoiding cumbersome purification. All of the varnishes had appropriate viscosities for film casting: 2300–6300 cP at 15 wt % concentration in a mixed solvent of γ-butyrolactone and N,N-dimethylacetamide. The solubility parameters of the obtained polymers were around 24.0 MPa1/2, close to that of N,N-dimethylacetamide; the densities and fractional free volumes of the polymer films were determined to be approximately 1.39 g/cm3 and 0.22, respectively. The polymer films were quite tough with an elastic modulus of up to 6.5 GPa and a tensile strength of up to 200 MPa, and their glass transition temperature reached 366 °C. A colorless and transparent film with a transmittance of 84.8% at 440 nm and a low yellow index of 1.77 was obtained by adding a bluing agent.