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

Abstract

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.