Hyperbranched Oxime-Ester Covalent Adaptive Network for Recyclable Ultralow-Dielectric Epoxy

Epoxy thermosets are indispensable in high-frequency (5G/6G) electronics, but their permanent crosslinks hinder recyclability and worsen e-waste. Although covalent adaptable networks (CANs) offer recyclability, their polar dynamic bonds exacerbate dielectric losses at gigahertz (GHz) bands due to dipolar relaxation. Here, we develop generation-tunable dendritic dynamic crosslinkers that yield recyclable epoxy-based printed circuit board (PCB) with ultralow dielectric performance. O-acylation reaction of a vanillin-derived tetrahedral aldoxime with phthalic anhydride affords precise control over generations, branching degree, and nanomorphology of the crosslinkers. This controlled synthesis yields porous coral-like architecture, which in turn produces graded-branched epoxy CANs with enhanced free volume and steric confinement. Within the rigid constrained topology, the network containing spherically distributed oxime-ester motifs exhibits restricted dipolar relaxation and achieves low dielectric loss in GHz bands, while remaining acid-cleavable for closed-loop recycling at 80 °C. The resulting PCB exhibits a record-low dielectric constant/loss (2.02/0.005@10 GHz), 71.53% improved X-band impedance matching, a tensile strength of 256 MPa, and V-0 flame retardancy, alongside a 98.9% reduction in ecotoxicity after recycling. This work demonstrates how precision dendrimer synthesis and topology regulation can reconcile the tradeoff between circularity and high-frequency performance in sustainable electronics.