Preparation and Characterization of Colorless Polyimide Films Containing Benzimidazole and Amide Groups Toward Thermally Stable Substrates for Next‐Gen Flexible Optoelectronics

ABSTRACT High‐performance polyimide (PI) films are highly valued for their exceptional comprehensive properties and are considered promising candidates for industrial production and application as optically transparent polymer materials. In this study, we introduced an asymmetric benzimidazole structure functionalized with amide groups via molecular engineering. The key molecular innovation lay in the synergistic integration of both benzimidazole and amide functionalities within the diamine (ABZ) skeleton. This design incorporated bulky side groups to reduce interchain packing efficiency, which enhanced solubility and processability, while the rigid biphenyl moieties helped offset any potential loss of thermal stability resulting from the disrupted chain packing. The diamine monomer was copolymerized with cyclobutane‐1,2,3,4‐tetracarboxylic dianhydride and 1,2,4,5‐cyclohexane tetracarboxylic dianhydride via a high‐temperature one‐step method to produce novel PI films. The resulting materials retained high thermal stability ( T d5% > 424°C) and demonstrated significantly improved overall performance with low coefficient of thermal expansion (29.5 ppm K −1 ), high optical transmittance (68% at 400 nm), and high glass transition temperatures ( T g > 359°C). They also exhibited excellent mechanical properties (tensile modulus E > 3.5 GPa, tensile strength σ > 137 MPa) and good solubility in common organic solvents. This strategy achieved an optimal balance between optical transparency, thermal stability, and mechanical performance, facilitating the development of high‐temperature‐suitable CPIs for next‐generation flexible electronics.