Embedded Direct Ink Writing of Thermoset and Elastomeric Polymers via Frontal Polymerization

ABSTRACT Direct ink writing (DIW) using frontal ring‐opening metathesis polymerization (FROMP) enables rapid, energy‐efficient fabrication of thermoset and elastomeric architectures through a self‐propagating exothermic curing reaction. However, FP‐DIW is constrained by stringent rheological requirements, feature‐size limits from front quenching, and the need for the reaction front to track the nozzle. Here, we overcome these constraints by leveraging embedded 3D printing to implement FP‐DIW with delayed solidification, thereby decoupling shape retention and solidification from ink chemistry and rheology. A yield‐stress support medium stabilizes low‐viscosity inks, suppresses gravitational and capillary instabilities, mitigates quenching at small diameters, and enables complex overlapping and mechanically interlinked features to fuse after deposition. Two thermal initiation strategies are introduced: volumetric dielectric heating via microwaves and surface heating at the support‐bath boundary. Dicyclopentadiene (DCPD), cyclooctadiene (COD), and mixed formulations provide tunable mechanical properties with glass transition temperatures from –50°C to 160°C. The approach enables lattices, springs, mechanically interlocked structures, and multimaterial architectures, substantially expanding the accessible material, feature‐size, and geometric design space compared with FP‐DIW in air.