Fabrication of high-performance polyimide films by tailoring coordination bond and chain rigidity

Coordination bonds and chain rigidities play severe roles in crystalline structure and property of polyimides (PIs). This study developed various polyimides with metal-diimine coordination bonds and varying chain rigidities. How coordination bonds and chain stiffness affect the semi-crystalline structure of polyimide films was investigated. Results from Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra confirmed the successful synthesis of coordinated polyimide films. Wide-angle diffraction (WAXD) results revealed that the crystallization behavior of PIs with flexible chains is significantly affected by additional coordination bonds, while the crystallization of PIs with rigid structures is primarily influenced by the chain rigidities. Compared to coordinated PIs with amorphous structure, PIs with both coordination bonds and semi-crystalline structures exhibited enhanced heat resistance, crystallinity, and dimensional stability. Notably, the coordinated PI-BP-Cu film with the highest chain rigidity in this study demonstrated excellent mechanical properties, with a tensile strength of 280 MPa, initial modulus of 5.7 GPa, and outstanding dimensional stability, characterized by a linear thermal expansion coefficient of 8.9 ppm/K (40–300 °C). These findings significantly enhance its suitability for use in metal/non-metal bonding composite materials.