Development of Polyimides with Low Dielectric Loss Tangent by Incorporating Polysiloxanes with Phenyl Side Groups

Abstract Owing to their low dielectric constant (Dk), processability, and mechanical properties, siloxane‐based polymers have attracted attention as insulating materials for next‐generation communication. However, a major challenge regarding siloxane‐containing materials is their high dielectric loss tangent (dissipation factor) (Df). A polymer is designed and synthesized by combining polysiloxanes with phenyl side groups on the main chain and a polyimide structure (polysiloxane‐imide) to improve the Df value. Compared with conventional dimethylsiloxane‐based polymers, the resulting polysiloxane‐imide, obtained as a bendable, self‐supporting film, exhibits a significantly reduced Df value. The rigidity of the phenyl group‐containing polysiloxane presumably contributes to the improvement in the Df value. Furthermore, polysiloxane‐imides exhibit excellent hydrophobicity and high heat resistance with their 5% weight loss temperature of over 400 °C. The synthesized polysiloxane‐imides with phenyl side groups, which possess various properties, including low Dk, low Df, and excellent hydrophobicity, are expected to contribute to the future practical application of siloxane‐based insulating materials.