Fabrication of Amide‐Incorporating Polyimide Films With Ultra‐Low <scp>CTE</scp> and High Mechanical Performance for Flexible Displays

ABSTRACT Flexible polyimide (PI) films with outstanding dimensional stability, great heat resistance and excellent mechanical performance were crucial to the application and reliability of flexible displays. In this study, a series of amide‐incorporating polyimides have been fabricated via the polycondensation of as‐synthesized dianhydride monomers (AMDA, m‐DAMDA, p‐DAMDA, F‐p‐DAMDA) and 4,4′‐diaminobenzanilide (DABA). The results revealed AMDA/DABA stood out for the sake of ultra‐low coefficient of thermal expansion (CTE) at 2.6 ppm K −1 , high glass transition temperature ( T g ) at 415°C and great tensile strength of 326 MPa, elongation at break of 13% and tensile modulus of 6.9 GPa, which resulted from a highly linear molecular backbone linked by numerous hydrogen bonds arising from amide groups. In particular, AMDA/DABA exhibited superior mechanical performance to pyromellitic dianhydride/4,4′‐diaminobenzanilide (PMDA/DABA: σ m = 261 MPa, ε b = 5.3%) and 4,4′‐biphthalic anhydride/4,4′‐diaminobenzanilide (BPDA/DABA: σ m = 174 MPa, ε b = 9.8%) previously reported. Hence, the AMDA/DABA film could be one of the promising candidates for application as polymer substrates for flexible displays.