Fig. 2

A FT-IR spectra of polyimide (PI) and PAA, with PI-B6 as a representative. The FT-IR spectrum of the representative PAA (B6) exhibited characteristic peaks at 1726 cm⁻¹ (carboxyl C=O) and 1661 cm⁻¹ (amide C=O stretching), as well as a peak at 1536 cm⁻¹ corresponding to amide C‒N stretching. In the FT-IR spectrum of the prepared PI (B6), the peaks for the amic acid groups disappeared, and the characteristic imide peaks at 1775 cm⁻¹ (imide C=O asymmetric stretching), 1722 cm⁻¹ (imide C=O symmetric stretching), and 1372 cm⁻¹ (imide C–N stretching) appeared, indicating complete imidization. B Appearance of the newly synthesized PI films