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

Owing to their low dielectric constant (D_k), 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) (D_f). 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 D_f value. Compared with conventional dimethylsiloxane-based polymers, the resulting polysiloxane-imide, obtained as a bendable, self-supporting film, exhibits a significantly reduced D_f value. The rigidity of the phenyl group-containing polysiloxane presumably contributes to the improvement in the D_f 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 D_k, low D_f, and excellent hydrophobicity, are expected to contribute to the future practical application of siloxane-based insulating materials.