High Heat-Resistant Polyimide Films Containing Quinoxaline Moiety for Flexible Substrate Applications

The development of thermostable polyimides (PIs) is urgently required for application in traditional aerospace and newly designing flexible-display substrates. The root to obtain intrinsic heat-resistant PIs is to seek novel monomers. Based on the high bond energy of quinoxaline, several quinoxaline diamines, including 3/2-(4-aminophenyl)-2/3-quinoxalin-6-amine (QHDA), 3/2-(4-aminophenyl)-2/3-phenyl quinoxalin-6-amine (QBDA), and 3/2-(4-aminophenyl)-2/3-methylquinoxalin-6-amine (QMDA) were synthesized, and the corresponding PI films were prepared with four aromatic dianhydrides. The introduction of a quinoxaline moiety provided the PI films with excellent thermal properties and an advanced mechanical performance. The QHDA-PIs possessed a high thermal stability with a 5% mass-loss temperature (T-d(5%)) of 528-560 degrees C, a glass-transition temperature (T-g) of 413-444 degrees C and a low coefficient of thermal expansion (CTE) of 1 ppm/K for QHDA-m because of its better linearity and closer packing. This study established design rules to tune the properties of quinoxaline PIs by sidegroup modification.