A “Bottom-Up”\nStrategy for High-Performance\nBenzocyclobutene (BCB)-Subnanometer Inorganic Nanocomposites

Developing benzocyclobutene (BCB) nanocomposites with\nultra-small\ninorganic sizes represents a formidable challenge, although it offers\ngreat potential to produce materials with customizable structural\nand rich functional properties. In this study, we present a “bottom-up”\ndesign strategy for creating cross-linked benzocyclobutene (BCB) nanocomposites\nwith highly dispersed nanodomains, such as organoalkoxysilane. This\napproach leverages ring-opening metathesis polymerization (ROMP) and\nthermally induced cycloaddition reactions to embed oligomeric silsesquioxanes,\nachieving a unique molecular structure with promising low-dielectric\napplications. The synthesis involves organoalkoxysilane and BCB as\npendant groups of polynorbornenes that are covalently integrated.\nAdditionally, the methoxyl groups of linear polymers could be further\nhydrolyzed under acidic conditions, and BCB groups could undergo thermal-induced\nring-opening at high temperatures and Diels–Alder addition\nbetween themselves and vinyl groups, respectively. Fourier transform\ninfrared (FTIR) spectroscopy analyses suggested the presence of ladder\nor network structures and high-resolution transmission electron microscopy\n(HRTEM) images presented the well-dispersed inorganic clusters, facilitating\nexcellent dielectric properties with a dielectric constant (<i>D</i><sub>k</sub>) of 2.25 and a dissipation factor (<i>D</i><sub>f</sub>) of 2.27 × 10<sup>–4</sup>. Compared\nwith previously reported low-<i>D</i><sub>k</sub> materials,\nthe cured nanocomposites also exhibited a significantly balanced enhancement\nof their comprehensive properties. This molecular bottom-up strategy\nprovided a simple and universal method for constructing BCB-inorganic\nnanocomposites featuring a subnanometer inorganic structure, paving\nthe way for future investigation into new classes of polymer–inorganic\nnanocomposites with a low <i>D</i><sub>k</sub>.