Investigating the properties of sulfone-containing transparent polyimide films through the combination of experimental and computational approaches

Abstract

In this study, two diamine monomers, 4,4′-(propane-2,2-diyl)bis(2-aminophenol) (PPAP) and 4,4′-sulfonyl bis(2-aminophenol) (SFAP), were copolymerized with three dianhydrides, 4,4′-(hexafluoroisopropylidene)phthalic anhydride (6FDA), cyclobutanetetracarboxylic dianhydride (CBDA), and 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA), to fabricate a series of colorless transparent polyimide (CPI) films. The influence of the diamine composition and the dianhydride type on the thermal, optical, and structural properties of the resulting films was systematically investigated. Theoretical calculations reveal that the designed molecular structures exhibit excellent transparency due to suppressed intramolecular charge transfer (ICT). Among the prepared films, CPI-1-6 exhibits the shortest charge transfer distance (5.545 Å), which effectively inhibits ICT and results in a pronounced blue shift in UV absorption (λ_max = 261.33 nm). Experiments show that the increase of SFAP content can improve the thermal stability. When PPAP : SFAP = 1 : 3 (CPI-1-3), the performance is optimal, T_g = 253.08 °C, T_d5% = 435.31 °C, and the optical performance is excellent (L* = 96.06, a* = −1.11, b* = 2.05). By comprehensive comparison, CPI-1-3 achieves the best balance between thermal stability and optical properties, which provides an important reference for the design of transparent polyimides for flexible displays.