Synthesis and characterization of tough colorless poly(amide‐imide)s containing cyclohexanedicarbonyl chloride with different trans:cis ratios.

With the rapid development of flexible optoelectronic devices, colorless polyimide films with excellent comprehensive performance have received widespread attention. In this work, a series of poly(amide‐imide)s (PAIs) were synthesized by copolymerization of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride, 1,4‐cyclohexanedicarbonyl chloride (CHDC) and 2,2′‐bis(trifluoromethyl)benzidine. The thermal dimensional stability and mechanical properties of the PAI films were improved due to the introduction of rigid rod‐like amide bonds in the polymer chain. In addition, the PAIs with more trans‐CHDC content showed higher glass transition temperature (Tg) and lower coefficient of thermal expansion (CTE). At the same time, the cooperative conformational transitions of cyclohexane rings in trans‐CHDC promoted molecular chain slip and improved the film toughness. Moreover, with the introduction of the cyclohexane moiety, these PAIs had excellent optical transparency and solubility. In particular, PAI‐6 exhibited high Tg of 364 °C, low CTE of 29.8 ppm K−1, high transmittance of 87% at 400 nm, tensile modulus of 3.6 GPa and elongation at break of 9.7%. Therefore, the incorporation of cyclohexane structures and amide bonds into the main chain through copolymerization with CHDC provided a simple method for the synthesis of tough colorless PAIs with excellent comprehensive properties. © 2025 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]