Green Approaches in Manufacturing Polyimides: From Eugenol-Based Monomers to Cross-Linked Polyimides with Low Dielectric Properties Utilizing γ-Valerolactone as the Solvent

High-performance polyimides (PIs) have attracted lots of interest in recent years and can be divided into categories such as colorless, low-dielectric, high thermal stability, etc. Nevertheless, the manufacturing process of PIs is not eco-friendly. In this circumstance, we focus on alleviating concerns related to solvents and monomers. In terms of solvents, we consider γ-valerolactone (GVL), dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP) as having similar physical and chemical properties. Given GVL’s low toxicity, we opt to use it as a replacement for toxic solvents. Regarding monomers, we utilize bioderived eugenol to synthesize bieugenol (BEu), from which we further develop two diamine monomers, BEu-d and BEu-s. Implementing chemical addition followed by radical cross-linking reactions and curing through a low-temperature thermal imidization method, we successfully produce a series of BEu-PI films. The BEu-PIs exhibit decent thermal stabilities and demonstrate notably low dielectric properties with D_k values ranging from 2.93 to 2.73 and D_f values from 7.8 to 6.9 × 10^-3, which are comparable to those of biobased low-k polymers and commercial PIs. All in all, these findings demonstrate a promising method for producing eco-friendly PIs with low dielectric properties, aiming to offer valuable insights for the realms of microelectronics and PIs.