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 (T_g) 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 T_g 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.