Comprehensive Performance of Polyimide Reinforced by Multiple Hydrogen Bonds for Flexible Electronics Application

Multiple hydrogen bonds (multi-HBs) can not only realize supramolecular polymerization but also significantly improve the mechanical properties of materials. Although it is known that hydrogen bonding can strengthen polymeric properties, the effect of multi-HBs has not been explored for high-performance polymers, especially polyimides (PIs). Here, a diamine monomer capable of forming multi-HBs, N,N′-(6-oxo-1,6-dihydropyrimidine-2,5-diyl)-bis(4-aminobenzamide) (DAPyBA), has been successfully designed and synthesized, and corresponding PI films have been prepared by polymerization of DAPyBA and 4,4-diaminodiphenyl ether (ODA) at different molar ratios with pyromellitic dianhydride (PMDA). All the PI films exhibited excellent heat resistance, with glass transition temperatures (T_g) ranging from 354 to 397 °C and 5% weight loss temperatures (T_d5) in the range from 455 to 574 °C. All the films also showed good mechanical properties and low coefficients of thermal expansion (CTE), and the mechanical properties and thermal dimensional stability of the PIs improved with increasing DAPyBA content due to the formation of multi-HBs. In particular, PI-50 presented a high tensile modulus (5.2 GPa), a low CTE (6.7 ppm K^–1), and a high T_g (354 °C), meeting the requirements of the flexible electronics and flexible printed circuit board. Meanwhile, the introduction of DAPyBA can effectively increase the adhesion of PI films on substrates due to the high contents of N and O atoms therein.