Transparent polyimide films with ultra-low coefficient of thermal expansion

According to the application requirements of colorless transparent polyimide (CPI) film for low coefficient of thermal expansion (CTE) in the field of OLED display, the new aromatic dianhydride monomers with amide bond structure were synthesized, namely s-ABDA, i-ABDA, EADA. Furthermore, a series of CPI films were prepared by two-step method from the reaction of as-synthesized dianhydrides with 2.2(')-bis (trifluoromethyl) -4.4(')-diaminobiphenyl (TFMB) or trans-1.4(')-cyclohexanediamine (t-CHDA). Based on the analysis of performance results, the incorporation of amide group and biphenyl, benzene or ether bond into dianhydride monomer helped this new type of transparent polyimide film with excellent optical properties (T-550 nm> 88%), great heat stability (CTE < 4.4 ppm/K; Tg > 314 degrees C; Td5% > 478 degrees C) and good mechanical strength (sigma > 208 MPa). The film s-ABDA/TFMB showed ultra-low CTE value at 4.4 ppm/K, aligning with the maximum birefringence, indicating that the role of hydrogen bonding was of great benefit to the regulation of thermal expansion.

Automated summary

New aromatic dianhydride monomers with amide bond structure were synthesized for the application of colorless transparent polyimide (CPI) film with low coefficient of thermal expansion (CTE) in the field of OLED display. CPI films were prepared and showed excellent optical properties, heat stability, and mechanical strength by incorporating amide groups and biphenyl, benzene, or ether bonds into the dianhydride monomer.