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.

Nowadays, more and more people are keen on investing in their own personal fitness. In this paper, a series of experiments were conducted to investigate the feasibility of using ethylene-vinyl acetate (EVA) foam for comfort fitting, with a special reference to shoes applications. Based on the experimental results obtained, it was concluded that the EVA foam examined in this study could satisfy most of the requirements for comfort fitting shoes in terms of shape fixity, shape recovery, and elasticity. The two problems spotted in this study may be easily solved by reducing the porosity ratio of the EVA foam and slightly decreasing the glass transition temperature of the foam.

Frontal ring-opening metathesis polymerization (FROMP) is a rapid, low-energy manufacturing reaction that is useful for curing thermosetting materials. FROMP of dicyclopentadiene (DCPD) results in poly­(dicyclopentadiene) (p­(DCPD)), a tough thermoset with excellent mechanical performance and chemical stability. Like most thermosets, p­(DCPD) cannot be reprocessed and is therefore difficult to recycle. Previous work demonstrated that the incorporation of a small quantity of cleavable units in the strand segments of p­(DCPD) networks enables their deconstruction. Here, we report that a commercially available multifunctional comonomer, 2,3-dihydrofuran (DHF), both acts as a potent Grubbs catalyst inhibitor during FROMP and introduces acid cleavable units. The resulting materials retain high performance characteristics, including glass-transition temperatures ranging from 115 to 165 °C and ultimate strength ranging from 35 to 40 MPa. The addition of DHF above critical loading levels enables deconstructable thermosets. We further demonstrate freeform three-dimensional (3D) printing of deconstructable thermosets via frontal polymerization.

significant challenges remain for rapid fabrication of complex structures with high strength, stiffness, and thermal stability. High-speed printing of complex, high-resolution structures has been achieved through photocuring, [13,14] but the thermomechanical properties are often inferior to thermally cured counterparts. DIW is an extrusion-based technique highly suitable for 3D printing thermally cured thermosets with excellent properties. [15] The ability to add reinforcing fibers and particles further enhances the engineering properties of DIW materials. [16,17] However, the inherent viscoelasticity of DIW inks invariably leads to creep and slumping of deposited structures, especially gap-spanning features, often limiting the size and geometrical complexity of the manufactured part. [11,[18][19][20] More recently, Qi and co-workers combined light-and thermal-curing resins to enable rapid initial solidification by photocuring followed by thermal post-curing to achieve desired engineering properties. [21,22] An alternative printing approach for thermoset resins relies on frontal polymerization (FP) during DIW to enable rapid curing of printed structures in tandem with the printing process. [23] FP is initiated by a thermal or photo stimulus, triggering an exothermic cure front that propagates by transport of heat and continued reaction in the monomer. During FP-DIW,The ability to manufacture highly intricate designs is one of the key advantages of 3D printing. Achieving high dimensional accuracy requires precise, often time-consuming calibration of the process parameters. Computerized feedback control systems for 3D printing enable sensing and real-time adaptation and optimization of these parameters at every stage of the print, but multiple challenges remain with sensor embedment and measurement accuracy. In contrast to these active control approaches, here, the authors harness frontal polymerization (FP) to rapidly cure extruded filament in tandem with the printing process. A temperature gradient present along the filament, which is dependent on the printing parameters, can impose control over this exothermic reaction. Experiments and theory reveal a self-regulative mechanism between filament temperature and cure kinetics that allows the frontal cure speed to autonomously match the print speed. This self-regulative printing process rapidly adapts to changes in print speed and environmental conditions to produce complex, high-fidelity structures and freestanding architectures spanning up to 100 mm, greatly expanding the capabilities of direct ink writing (DIW).