Covalent Adaptable Networks with Dual Dynamic Covalent Bonds for Self-Repairing Infrared Transmitting Materials

Infrared transmitting materials (IRTMs) are prone to mechanical and corrosion damage during long-time exposure to harsh outside environments. However, conventional IRTMs frequently lack self-repairability that limit their lifespan. To address the limitation, thioctic acid-based epoxy resins (TAEs) are developed from natural thioctic acid and commercial epoxy monomers. The double ring-opening polymerization (ROP) reactions of thioctic acid and epoxy groups result in dual dynamic covalent bonds with varying bond energies containing relatively weak disulfide bonds and strong ester bonds. As compared with conventional covalent adaptable networks (CANs) that present rapid creep properties when heated, TAEs maintain their geometric stability during rapid self-repairing at a mild temperature of 80 °C by enhancing network integrity through stable ester crosslinking points. The feature renders TAEs self-repairing capability while maintaining precise geometrical dimensions, which is suitable for infrared transmitting devices. On the other hand, TAEs exhibit high near-infrared transmittance (>80%). Therefore, TAEs with self-repairability and high infrared transmittance demonstrate they can be used as superior polymeric IRTM.