Multi-Generation Recycling of Thermosets Enabled by Fragment Reactivation.

Thermosets are used in numerous industrial applications due to their excellent stabilities and mechanical properties; however, their covalently cross-linked structures limit chemical circularity. Cleavable comonomers (CCs) offer a practical strategy to impart new end-of-life opportunities, such as deconstructability or remoldability, to thermosets without altering critical properties, cost, or manufacturing workflows. Nevertheless, CC-enabled recycling of thermosets has so far been limited to one cycle with a 25% recycled content. Here, we introduce a "fragment reactivation" strategy, wherein the oligomeric fragments obtained from CC-enabled thermoset deconstruction are activated with functional groups that improve fragment solubility and reactivity for subsequent rounds of recycling. Using polydicyclopentadiene (pDCPD), an industrial hydrocarbon thermoset material, containing low loadings of a siloxane-based CC, we first demonstrate two rounds of chemical recycling by incorporating 40 wt % norbornene silyl ether-reactivated fragments derived from the prior generation's deconstruction. Then, we show that the two-step sequence of deconstruction and reactivation can be unified into a single-step process, referred to as "deconstructive reactivation." Using this approach, we demonstrate three rounds of chemical recycling with 40-45 wt % fragments incorporated per cycle while maintaining key material properties and deconstructability. These three generations of recycling effectively extend the lifespan of deconstructable pDCPD thermosets by ∼2.6 times. Combined with CCs, fragment reactivation presents a promising and potentially generalizable strategy to improve the chemical recycling efficiency of thermosets.