Ultrastrong, Ductile, Tear- and Folding-Resistant Polyimide Film Doubly Reinforced by an Aminated Rigid-Rod Macromolecule and Graphene Oxide

As a high-performance polymer with exceptional mechanical, thermal, and insulating properties, polyimide (PI) has been widely used as flexible circuit substrates for microelectronics, portable electronics, and wearable devices. Due to the growing demand for further thinning and lightweighting of electronic products, PI films need to have further enhanced mechanical properties. Traditional nanofiller-reinforced PI films often exhibit reduced ductility and limited improvements in strength. Therefore, it remains a challenge to simultaneously improve the strength and toughness of PI films while preserving their ductility. In this study, we report an exceptionally strong and ductile PI doubly reinforced by one-dimensional rigid-rod para-aramid, poly(p-aminophenylene aminoterephthalamide ((NH2)(2)-PPTA), and two-dimensional graphene oxide (GO) nanosheets. The amino side groups of (NH2)(2)-PPTA react with the anhydride end groups of PI, forming covalent bonds. At a (NH2)(2)-PPTA content of only 0.4 wt %, the (NH2)(2)-PPTA/PI film displays significantly enhanced mechanical properties. When 0.4 wt % of GO is added together with (NH2)(2)-PPTA, the tensile strength, tensile toughness, and strain at break reach 284.8 +/- 5.3 MPa, 277.9 +/- 7.6 MJ/m(3), and 132.6 +/- 3.8%, which are similar to 178, similar to 312, and similar to 51% higher, respectively, than those of pure PI. Moreover, the doubly reinforced PI film also exhibits a 206% increase in tear strength and significantly enhanced folding resistance. The dual reinforcement of PI with (NH2)(2)-PPTA and GO improves the mechanical properties more efficiently than any single reinforcing agents previously reported and overcomes the disadvantage of most inorganic nanofillers that reduce ductility.