Bicontinuous polycyanurate/ethynyl-resin linked interpenetrating polymer networks via interphase-controlled nanophase separation with high toughness and low dielectric constant

High-performance printed circuit board (PCB) substrates require polymer matrices combining high thermal stability, mechanical robustness, and low dielectric constant. However, conventional polycyanurate resins suffer from intrinsic brittleness owing to highly crosslinked triazine networks, limiting their broader use in advanced PCB substrates. Herein, we developed nanophase-separated linked interpenetrating polymer networks (LIPNs) based on bisphenol A dicyanate (BADCy) and ethynyl phenyl azophenol-biphenylene resins (EPABNs). By regulating nanophase-separated domains (R_m) and interfacial thickness (l_int), the toughness of the LIPNs was significantly improved. The LIPNs were constructed via a gradient temperature curing protocol, during which iminocarbonate linkers formed in situ to chemically bridge the networks and suppress macrophase separation. By tuning the linkers and ethynyl content, the LIPNs exhibited a transition from agglomerated domains to a highly interconnected bicontinuous morphology, accompanied by systematic changes in l_int and segmental dynamics. Dynamic mechanical analysis (DMA) and small-angle X-ray scattering (SAXS) reveal balanced interfacial confinement and coordinated segmental dynamics in the optimized LIPN. As a result, the optimized polycyanurate/ethynyl-resin LIPN achieved a high glass transition temperature (T_g) of 274 °C, a flexural modulus of 3.2 GPa, and an impact strength of 30 kJ m⁻². Furthermore, basalt fiber reinforced polymer composites (BFRPCs) based on this LIPN exhibited a low dielectric constant of 2.84 at 1 MHz and a high flexural strength of 566 MPa. The reduced dielectric constant is attributed to the dense interconnected network, which restricts polar-group mobility and mitigates moisture-induced interfacial polarization. This work highlights interphase-controlled nanophase separation as an effective strategy for constructing toughened polycyanurate LIPNs for high-performance PCB substrates.