Solvable bio-based intrinsic black polyimides containing furanyl-pyridine units: synthesis, structures and properties

Black Polyimides (BPIs) have very important prospectives in aerospace, microelectronics, and advanced optical devices. To the aim, three bio-based aromatic diamines containing furanyl-pyridine units, such as 4-furanyl-2,6-(4-aminophenyl)pyridine (PFDA), O-FPDA with ether bond (−O-) and 6F-FPDA with −CF₃ groups, were designed and successfully synthesized via the Hantzsch reaction using the furfural as original materials. More fine structures of three diamines were determined by using FT-IR, ¹HNMR and XRD analysis. Then, the novel intrinsic BPIs, such as FPPI, O-FPPI and 6F-FPPI, were prepared by polycondensation between three diamines and pyromellitic dianhydride (PMDA), respectively. All BPIs exhibit excellent solubility in many polar solvents such as DMF, DMAc, and DMSO at room temperature. Among them, FPPI and O-FPPI are easily dissolved in low-boiling point solvents such as tetrahydrofuran (THF), which would provide the better formability and processability. Under N₂ atmosphere, these BPIs also show the outstanding thermal stability. Especially, O-FPPI sample displays the initial thermal decomposition temperature (T₅) of 478 °C and the residual carbon rate (Y_c) of over 71 % at 800 °C. Meanwhile, all BPI films exhibit the super-strong light absorption in UV–Vis districts. FPPI film has almost full spectrum absorption, with the cutoff wavelength (λ_cut) about 702 nm and the relative transmittance only of 2.85 % at 760 nm. Due to these outstanding properties and bio-based characteristics, these diamines with furanyl-pyridine units could provide the green renewability and easy availability of raw materials for BPIs in the future sustainable applications.