Non-contact photothermal initiation of frontal polymerization during 3D printing of polymer composites

Frontal polymerization (FP) offers a rapid and energy-efficient strategy for curing thermoset polymers and their composites during additive manufacturing (AM) processes. Current approaches for initiating FP in FP-enabled AM rely on heated beds or manual contact methods, which limit scalability, process control, and full automation. Here, we demonstrate a compact, low-power laser-based photothermal system capable of remotely initiating FP during direct ink writing (DIW) of thermoset composites. Reliable, sub-second FP initiation is achieved in an epoxy-vinyl ether formulation with energy inputs below 1.5 J, enabling spatially and temporally programmable curing. The effect of various material and process parameters on initiation time are systematically characterized. In addition, multi-point initiation is used to reduce overall cure time in complex geometries and multi-layered structures. The strategy is extended to a dicyclopentadiene-based resin system to fabricate a freeform helical structure cured in midair. Photothermal FP initiation is thereby established as a versatile and broadly applicable technique for 3D printing of thermoset composites, offering precise control over the timing and location of curing.