Synthesis and characterization of amide-bridged colorless polyimide films with low CTE and high optical performance for flexible OLED displays

Three novel dianhydride monomers involving amide groups were synthesized and further polymerized with various diamines to afford a series of colorless polyimides (cPI). The resultant cPI films present outstanding optical performance, exceedingly good dimensional stability at high temperature, great film ductility and solution-processability. In particular, chemically imidized AMDA/TFDB has an ultra-low coefficient of thermal expansion value of 5.2 ppm K-A, a relatively high T-g value of 333 degrees C and large elongation at break of 29%, resulting from its rigid-rod backbone and the formation of hydrogen bonding (-C=O center dot center dot center dot NH-) between adjacent molecular chains. Concurrently, it exhibits a high optical transmittance of 87% at a wavelength of 550 nm, a small haze value of 0.71 and low yellow index of 4.29 by reason that the incorporation of bulky trifluoromethyl and cyclohexyl preclude the formation of a charge transfer complex effectively. The high overall performance of the amide-containing cPI films suggests its potential application in the field of flexible OLED displays.

Automated summary

Three novel dianhydride monomers with amide groups were synthesized and polymerized to produce colorless polyimides with excellent optical performance, thermal stability, film ductility, and solution-processability. One of the polyimides exhibited ultra-low thermal expansion coefficient, high T-g value, and large elongation at break due to its rigid-rod backbone and hydrogen bonding between molecular chains. The incorporation of bulky trifluoromethyl and cyclohexyl groups resulted in high optical transmittance, low haze, and low yellow index, indicating potential application in flexible OLED displays.