Liquid Crystalline Siloxane-Containing Poly(ester imide)s with Low Dielectric Constant and Low Dielectric Loss at 10...

The development of high-performance polymers exhibiting both low dielectric constant (D_k) and low dielectric loss (D_f) at high frequencies is highly desirable yet challenging for applications in microelectronics and wireless communication technologies. In this work, a series of siloxane-containing poly(ester imide)s (SiPEIs) are designed and synthesized via a two-step polymerization route, using 1,4-phenylene bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate) (TAHQ) as the dianhydride monomer, and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (DMS) together with 4,4'-diaminodiphenyl ether (ODA) as the diamine comonomers. Although the introduction of short siloxane segments lowers the glass transition temperature (T_g) and the tensile strength of the resulting PEIs, they still remain at a relatively high level. Liquid crystalline phase behavior is observed at lower temperature for the siloxane-containing PEIs. Meanwhile, the hydrophobicity and the high-frequency dielectric performance is effectively improved with increasing siloxane content. Notably, SiPEI-20, prepared with 20 mol% DMS, displays an outstanding integrated performance. It exhibits a T_g of 200 °C, a D_k of 2.87 and a D_f of 0.00155 at 10 GHz, as well as an adhesive strength of 0.85 N·mm^-1 on copper foil. Overall, this work provides a feasible strategy by incorporating siloxane into the PEI backbone, enabling the synergistic enhancement of high-frequency dielectric properties (simultaneous reduction in D_k and D_f) and adhesion to copper foil.