Realizing Excellent Thermal Properties and Optical Transmittance of Polyimides With Amide‐Containing Diamine and Fluorinated Triamine Monomers for Flexible Display and Electronics

ABSTRACT Polyimide (PI) films are very promising as substrates for flexible displays, flexible electronics, and so on. It is expected that they are not only thermally resistant, but also colorless, and mechanically robust. In this work, PIs were chemically synthesized from designed monomers by polycondensation. The monomers such as N , N ′‐(2,2′‐bis(trifluoromethyl)‐[1,1′‐biphenyl]‐4,4′‐diyl)bis(4‐aminobenzamide) (AB‐TFMB) and trifluoromethyl containing triamine 4,4′,4″‐(benzene‐1,3,5‐triyltris(oxy))tris(3‐(trifluoromethyl)aniline) (TFAPOB), together with other commercial monomers, namely 2,2′‐bis(trifluoromethyl)benzidine (TFMB), 2,2′‐dimethyl[1,1′‐biphenyl]‐4,4′‐diamine (DMBZ) were adopted during polymerization. The PI film embedded with hydrogen‐bonding, methyl‐substituted biphenyl, and micro‐cross‐links demonstrates the best overall properties, with a glass transition temperature ( T g ) of 406°C, coefficient of thermal expansion (CTE) of 19.7 ppm/K, transmittance of 80.4% at 450 nm ( T 450 ), tensile strength ( σ ) of 152 MPa, and an elongation at break ( ε ) of 10.2%. These results reflect that it is possible to achieve excellent comprehensive properties of PI film by reasonable molecular design.