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

The development of high-performance polymers exhibiting both low dielectric constant (Dk) and low dielectric loss (Df) 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 (Tg) 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 aTgof 200 °C, a Dkof 2.87 and a Dfof 0.00155 at 10 GHz, as well as an adhesive strength of 0.85 N·mm−1on 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 Dkand Df) and adhesion to copper foil.