Programmable topological regulation of hierarchically organized crosslinked epoxy thermosets for improved dielectric and thermal properties

Abstract

Thermosetting epoxy resins with low dielectric loss and high thermal stability are highly desirable for high-frequency electronic applications, yet these properties remain difficult to balance because reducing polarity in conventional curing systems often compromises intermolecular cohesion. Herein, a series of vinyl-functionalized active esters were synthesized to introduce a programmable vinyl-mediated curing motif into epoxy thermosets. Spectroscopic and calorimetric analyses revealed that ester–epoxy coupling dominated the early curing stage, generating a low-polarity primary network, whereas vinyl crosslinking remained kinetically suppressed until higher temperatures and conversion levels were reached. This programmed “epoxy-first, then vinyl” curing pathway subsequently enabled delayed vinyl polymerization to lock the pre-formed epoxy matrix, thereby generating a hierarchically organized crosslinked network. As a result, the optimized thermoset exhibited a dielectric constant of 2.90 and a dielectric loss of 0.0051 at 10 GHz, together with a high glass-transition temperature of 198 °C, a reduced coefficient of thermal expansion of 54.7 ppm K⁻¹, and a tensile strength of 65.2 MPa. Dynamic mechanical, thermomechanical, and thermal analyses further suggested enhanced molecular confinement and increased crosslink density induced by the late-stage polyvinyl network locking process. Overall, these findings show that programmed sequential curing can serve as a promising route to alleviate the conventional trade-off between dielectric and thermal–mechanical properties, providing a useful strategy for designing low-loss thermosetting dielectrics through network evolution control rather than simple compositional modification.