Rapid Chemical Recycling of Eugenol-Derived Epoxy Thermosets via Cleavable Silyl Ether Linkages with High Chemical Recovery

A chemically depolymerizable eugenol-based epoxy resin (SE-EP) containing cleavable silyl ether linkages was successfully synthesized. The SE-EP was cured with methyltetrahydrophthalic anhydride (MeTHPA) to form a cross-linked network with a cross-link density of 0.00145 mol·cm–3. The resulting SE-EP/MeTHPA thermoset exhibited excellent mechanical and thermal properties, including a tensile strength of 23 MPa, a modulus of 800 MPa, an elongation at break of 6.3%, and a glass transition temperature of 51 °C. Remarkably, in mildly acidic conditions (0.01–0.20 M HCl at 50 °C), the network exhibited rapid chemical depolymerization following a pseudo-first-order rate constant of k = 0.162 min–1, demonstrating a reaction rate 10,000 times faster than that of previously reported chemically depolymerizable epoxy resins. Crucially, FT-IR, 1H NMR, and GC-MS analyses confirmed the selective cleavage of the Si–O bonds and the almost quantitative recovery of the eugenol-derived materials. Specifically, 96% of the eugenol-derived monomers and 86% of the MeTHPA curing agent-derived monomers were successfully recovered. The ability to recover these monomers with such high yield and purity offers an excellent recycling method for circular resource management, as it enables the repetitive reuse of the feedstock-derived species while maintaining favorable mechanical and thermal performance in the resulting polymer, unlike conventional recycling. Therefore, the introduction of silyl ether bonds provides an effective molecular design strategy for achieving rapid chemical depolymerization and high-value circularity while maintaining the desired mechanical properties of epoxy thermosets.