Orthogonal Monomer Design Enables Sequentially Cured Hybrid Polymers for Ultralow‐Dielectric Applications

ABSTRACT Precise molecular design and orthogonal reaction pathways offer powerful tools for engineering polymer networks with controlled nanoscale architectures and advanced dielectric properties. Herein, we report an orthogonal monomer design strategy that integrates ring‐opening metathesis polymerization (ROMP), photodimerization, and thermally induced benzocyclobutene (BCB) crosslinking to construct hybrid polymers with sequentially cured, nanoconfined silsesquioxane (SSQ) domains. The modular incorporation of photoreactive anthracene and thermally active BCB units into ROMP‐compatible monomers enables chemically decoupled dual curing. This sequential crosslinking allows precise spatial confinement of SSQ domains within a covalent organic matrix, effectively minimizing interfacial defects and phase separation. The resulting hybrid networks exhibit an ultralow dielectric constant ( D k = 2.08), extremely low dissipation factor ( D f = 6.67 × 10 −4 ), high thermal stability (the 5% weight loss temperature, T d5 > 400°C), hydrophobic surfaces (water contact angle > 100°), and robust mechanical integrity. This work highlights a generalizable chemical design paradigm that links orthogonal monomer reactivity to nanoscale structure control and multifunctional dielectric performance, offering a promising pathway for advanced electronic packaging materials.