Polyimide films with high strength and toughness synthesized utilizing a synergistic strategy of stiffness-flexibility harmonization

In this manuscript, polyimide (PI) films with high strength and toughness are achieved by adjusting the stiffness and flexibility of the PI macromolecules utilizing rigid mixed diamine monomers, namely benzimidazole (PABZ) /benzoxazole (BOA) and flexible bisphenol A dianhydride (BPADA) monomer. Meanwhile, the stiffness of the PI is modulated as well by the coordination crosslinking between benzimidazole motifs of PABZ and Cu 2+ validated by FTIR, XPS and UV-vis spectra, respectively which could boost the arrangement and packing of the PI molecules confirmed by the packing coefficient. The comprehensive properties of the polyimide film are synergistically increased by combining the rigidity/flexibility of the macromolecules and the reversible coordination effect, with a strength and toughness of the PI film reaching 132.43 ± 1.73 MPa and 21.24 ± 2.13 MJ/m 3 respectively, as well as the decomposition temperature 5% weight loss (T d5% ) and glass transition temperature (Tg) attaining at 514°C and 251°C. More interestingly, the PI films exhibit excellent wear resistance with the volume wear rate reduced from 15.578 × 10 -6 mm 3 /Nm to 2.936 × 10 -6 mm 3 /Nm which accounts for a reduction of 81.2% compared to neat PI. Therefore, high-strength/toughness, improved thermal stability and excellent wear-resistant PI films can be fabricated utilizing a synergistic strategy of stiffness-flexibility harmonization which is expected to provide a novel design strategy for the high-performance PI application.