Synthesis of High-Performance Colorless Polyimides with Asymmetric Diamine: Application in Flexible Electronic...

Colorless polyimides (CPIs) are widely used as high-performance materials in flexible electronic devices. From a molecular design standpoint, the industry continues to encounter challenges in developing CPIs with desired attributes, including exceptional optical transparency, excellent thermal stability, and enhanced mechanical strength. This study presents and validates a method for controlling 2-substituents, with a specific emphasis on examining how these substituents affect the thermal, mechanical, optical, and dielectric characteristics of CPIs. The presence of two CF₃ groups on the same side of the diamine structure ensured the transmittance of the film. The charge transfer effect and the molecular distance are dynamically regulated by changing the 2-substituent (-OCH₃/-CH₃/H/F). The polyimide exhibited a well-maintained equilibrium between transparency and thermal stability, with a T_500nm value ranging from 86.2 to 89.6% in the visible region, and a glass transition temperature (T_g) ranging from 358.6 to 376.0 °C. Additionally, the 6FDA-2-MTFMB compound, when combined with methyl, excels as a protective layer and base material, exhibiting excellent performance in various aspects. It has been verified as an appropriate option for flexible photodetectors and wearable piezoresistive sensors. In summary, this systematic investigation will provide a comprehensive and demonstrative methodology for developing CPIs that are capable of adapting to flexible electronic devices.