Thermoset polymers and composite materials are integral to today's aerospace, automotive, marine and energy industries and will be vital to the next generation of lightweight, energy-efficient structures in these enterprises, owing to their excellent specific stiffness and strength, thermal stability and chemical resistance. The manufacture of high-performance thermoset components requires the monomer to be cured at high temperatures (around 180 °C) for several hours, under a combined external pressure and internal vacuum . Curing is generally accomplished using large autoclaves or ovens that scale in size with the component. Hence this traditional curing approach is slow, requires a large amount of energy and involves substantial capital investment. Frontal polymerization is a promising alternative curing strategy, in which a self-propagating exothermic reaction wave transforms liquid monomers to fully cured polymers. We report here the frontal polymerization of a high-performance thermoset polymer that allows the rapid fabrication of parts with microscale features, three-dimensional printed structures and carbon-fibre-reinforced polymer composites. Precise control of the polymerization kinetics at both ambient and elevated temperatures allows stable monomer solutions to transform into fully cured polymers within seconds, reducing energy requirements and cure times by several orders of magnitude compared with conventional oven or autoclave curing approaches. The resulting polymer and composite parts possess similar mechanical properties to those cured conventionally. This curing strategy greatly improves the efficiency of manufacturing of high-performance polymers and composites, and is widely applicable to many industries.

Bioinspired vascular networks transport heat and mass in hydrogels, microfluidic devices, self-healing and self-cooling structures, filters, and flow batteries. Lengthy, multistep fabrication processes involving solvents, external heat, and vacuum hinder large-scale application of vascular networks in structural materials. Here, we report the rapid (seconds to minutes), scalable, and synchronized fabrication of vascular thermosets and fiber-reinforced composites under ambient conditions. The exothermic frontal polymerization (FP) of a liquid or gelled resin facilitates coordinated depolymerization of an embedded sacrificial template to create host structures with high-fidelity interconnected microchannels. The chemical energy released during matrix polymerization eliminates the need for a sustained external heat source and greatly reduces external energy consumption for processing. Programming the rate of depolymerization of the sacrificial thermoplastic to match the kinetics of FP has the potential to significantly expedite the fabrication of vascular structures with extended lifetimes, microreactors, and imaging phantoms for understanding capillary flow in biological systems.

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The retention and transport of different fluids inside synthetic microvascular fiber-reinforced polymer (FRP) composites enable environmentally adaptive functions, including thermal regulation, self-healing, and electromagnetic modulation. However, manufacturing of vascularized components involves an energy- and time-intensive multistep process to cure the host matrix (several hours at elevated temperature) and then evacuate the embedded sacrificial template (12–24 h at 200°C under vacuum). Here, we demonstrate rapid (minutes), energy-efficient, and scalable fabrication of vascularized FRP composites at room temperature using the exothermic frontal polymerization of a dicyclopentadiene host matrix. The chemical energy released during frontal curing of the host resin facilitates the endothermic depolymerization of an embedded sacrificial thermoplastic to create structures with high-fidelity microchannels, reducing the thermal energy for fabrication by nearly four orders of magnitude compared to previous methods. The presence of fiber reinforcement in this tandem curing and vascularization strategy presents several challenges related to successful frontal curing and microchannel formation. Increasing the volume fraction of fiber reinforcement ( Vf) decreases the volume of the host resin matrix, generating less energy for sustaining the curing and vascularization processes. Heat retention for several minutes after completion of frontal curing using thermally insulating tooling is crucial for obtaining clear microchannels in composite specimens with Vf = 60%. Simulation of the vascularization process confirms the slower depolymerization of the sacrificial templates in high- Vf composites. A nominal decrease in channel circularity also occurs with an increase in the compaction pressure required for high Vf of composite panels. We leverage this rapid manufacturing strategy to fabricate hybrid composites with vascular networks that span the bulk of the composite and a surface coating for potential self-healing applications.

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