Facile synthesis of high-performance colorless polyimide films bearing amide groups with enhanced optical and thermal stability

The rapid development of flexible displays has spurred the rational design and performance optimization of colorless polyimide films (CPI) with superior integrated properties. In this work, a series of amide-bridged CPI films were fabricated via polycondensation of the as-synthesized dianhydrides ( p -DAMDA, m -DAMDA, F-DAMDA) with commercial diamines, including 2,2′-bis(trifluoromethyl)benzidine (TFDB) and trans-1,4-diaminocyclohexane (t-CHDA). The results demonstrated p -DAMDA/TFDB exhibited the most favorable comprehensive performance, featuring a high optical transmittance of 86% at 550 nm, a low CTE value of 8.7 ppm K -1 and a relatively high T g of 334°C. Besides, the effects of meta-substituted structure and aromatic fluorination on the optical and thermal properties of as-prepared CPI films were systematically investigated. The results showed the aromatic fluorination (i.e., hydrogen atoms substituted by fluorine), effectively enhanced the optical performance while retaining excellent dimensional stability. For instance, the optical transmittance and CTE value of F-DAMDA/t-CHDA film reached 87% and 16 ppm K -1 , respectively. By contrast, the introduction of meta-substituted structure disrupted the ordered packing of molecular chains and increased the free volume, thus leading to an elevated CTE and deteriorated thermal dimensional stability, even though a relatively high optical transparency was retained. As a representative example, the m -DAMDA/t-CHDA film showed an optical transmittance of 86% and a CTE value of 35.3 ppm K -1 , respectively. This work provided valuable insights into the structure-performance relationship of amide-bridged CPI films, offering a feasible molecular design strategy for advanced flexible electronic applications.