Ultralow Dielectric Benzocyclobutene Nanocomposites via Subnanometer Engineering of Covalently Dispersed Silsesquioxane Domains

Next-generation, high-frequency communication systems demand polymer nanocomposites with simultaneously ultralow dielectric constant (Dk < 2.0) and high thermomechanical stability while addressing the critical challenge of reconciling nanoscale dispersion uniformity with interfacial compatibility. Herein, we propose a molecular engineering strategy to covalently anchor oligomeric silsesquioxane domains within a benzocyclobutene resin (BCB) matrix via synergistic click chemistry and thermally triggered Diels–Alder cross-linking. The silsesquioxane precursors are precisely synthesized through platinum-catalyzed hydrosilylation and hydrolysis-polycondensation, enabling the formation of ladder/cage-like and networked Si–O–Si structures. This covalent integration strategy ensures uniform silsesquioxane dispersion at the subnanoscale, as evidenced by small-angle X-ray scattering (SAXS) and high-resolution transmission electron microscopy (TEM). The optimized nanocomposite exhibits an ultralow dielectric constant (Dk = 1.78) and loss (Df = 2.73 × 10–3) at 1.15 kHz, outperforming most reported BCB hybrids. This work establishes a molecular-scale engineering paradigm for low-Dk materials, offering transformative potential in 5G/6G communications and high-density integrated circuit technologies.