Catalytic Arene-Norbornene Annulation toward All-Hydrocarbon Benzocyclobutene-Based Polymers with Ultralow Dielectric Constants

The development of ultralow dielectric constant (Dk < 2.5) materials with high thermal stability and mechanical robustness faces a critical bottleneck: traditional strategies relying on fluorination or nanoporosity inevitably compromise processability or environmental compatibility. Here, we report a catalytic arene-norbornene annulation (CANAL) strategy to synthesize all-hydrocarbon benzocyclobutene (BCB)-based polymers with intrinsic microporosity. By leveraging the rigid and twisted norbornene-bridged BCB architecture, the optimized polymer (P-NBD-BCB) achieves an ultralow Dk of 2.37 at 10 GHz. Combined experimental and computational analyses reveal that the synergy between norbornene-induced free volume (22.2%) and suppressed chain polarization underpins the reduced dielectric constants, while Diels–Alder cross-linking stabilizes the network against thermal decomposition (Td5% = 483 °C). The material further demonstrates 5G-compatible dielectric loss and exceptional mechanical properties. This work establishes a robust strategy for designing sustainable ultralow dielectrics through precise control of hydrocarbon topology, addressing the escalating demands of high-frequency communication and three-dimensional heterogeneous integration.