Ultrastrong, Ductile,\nTear- and Folding-Resistant\nPolyimide Film Doubly Reinforced by an Aminated Rigid-Rod Macromolecule\nand Graphene Oxide

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