Synthesis and properties of low-dielectric hydrophobic polyimides containing alkyl groups and ortho ‑phthalic structures

In this study, two novel aromatic diamine monomers (TBA and DTBA) containing methyl, tert‑butyl and ortho-phthalic twisted structures were designed via molecular design. A series of polyimides were subsequently prepared by one‑step high‑temperature solution polycondensation of these diamines with three dianhydride monomers, namely BPDA, BPADA and ODPA, respectively. The synergistic effects of the introduced bulky side groups and twisted non‑coplanar structures on the solubility, thermal properties, mechanical properties, optical transparency, dielectric constant and hydrophobicity of the resulting polyimides were systematically investigated. The results show that all polyimides exhibit amorphous structures and good solubility. Their glass transition temperatures range from 208 to 292 °C, and the thermal decomposition temperatures were above 500 °C, demonstrating excellent thermal stability. Meanwhile, the polyimide films exhibit low dielectric constants (2.77–2.93 at 1 kHz) and good hydrophobicity (water contact angles in the range of 90.7°–99.8°). This study provides an effective molecular design strategy for developing high‑performance polyimides combining low dielectric constant, hydrophobicity and good processability, showing their potential for application in high‑frequency microelectronic devices.