Preparation and Characterization of Colorless and Transparent Polyimide Films With Excellent Thermal Stability for Flexible Displays

ABSTRACT Colorless and transparent polyimide films (CPIs) have gained widespread attention as a crucial substrate material for flexible organic light‐emitting diode (OLED) displays. This study discusses the synthesis of a series of CPI films (CPI‐X) featuring novel structures, using diamine monomers containing highly electronegative sulfone groups (m‐BAPS), dianhydride monomers with fluoroalkyl groups (6FDA), and dianhydride monomers with noncoplanar structures (a‐BPDA). The successful synthesis of the CPI films was confirmed through FTIR, 1 H NMR, and XRD. The optical properties were optimized by adjusting the ratio of dianhydride monomers, and UV–vis tests indicated that the CPI‐6 film exhibited superior transmittance, reaching 86% at 450 nm. Notably, these films displayed excellent thermal stability, with a maximum thermal decomposition temperature at 5% weight loss of 476.2°C, which may be attributed to the synergistic interaction between the two dianhydrides achieving an optimal thermodynamic balance between molecular packing density and free volume. Additionally, the CPI‐6 film demonstrated exceptional folding endurance, showing no significant surface changes after 10,000 folding cycles. In summary, this study provides a novel and effective structural design for high‐performance CPIs in the flexible electronics field.