Green Approaches in Manufacturing Polyimides: From\nEugenol-Based Monomers to Cross-Linked Polyimides with Low Dielectric\nProperties Utilizing γ‑Valerolactone as the Solvent

High-performance\npolyimides (PIs) have attracted lots of interest\nin recent years and can be divided into categories such as colorless,\nlow-dielectric, high thermal stability, etc. Nevertheless, the manufacturing\nprocess of PIs is not eco-friendly. In this circumstance, we focus\non alleviating concerns related to solvents and monomers. In terms\nof solvents, we consider γ-valerolactone (GVL), dimethylformamide\n(DMF), and <i>N</i>-methyl-2-pyrrolidone (NMP) as having\nsimilar physical and chemical properties. Given GVL’s low toxicity,\nwe opt to use it as a replacement for toxic solvents. Regarding monomers,\nwe utilize bioderived eugenol to synthesize bieugenol (BEu), from\nwhich we further develop two diamine monomers, BEu-d and BEu-s. Implementing\nchemical addition followed by radical cross-linking reactions and\ncuring through a low-temperature thermal imidization method, we successfully\nproduce a series of BEu-PI films. The BEu-PIs exhibit decent thermal\nstabilities and demonstrate notably low dielectric properties with <i>D</i><sub>k</sub> values ranging from 2.93 to 2.73 and <i>D</i><sub>f</sub> values from 7.8 to 6.9 × 10<sup>–3</sup>, which are comparable to those of biobased low-<i>k</i> polymers and commercial PIs. All in all, these findings demonstrate\na promising method for producing eco-friendly PIs with low dielectric\nproperties, aiming to offer valuable insights for the realms of microelectronics\nand PIs.