Heterogeneous waste integration of PET and cyanate ester thermosets for developing fully upcyclable co-crosslinked polymers via nucleophilic aromatic substitution

The exponential accumulation of polymeric waste presents a critical environmental challenge. Recycling thermosets remains particularly formidable compared to thermoplastics due to their intractable, permanently crosslinked networks. Addressing this, chemical strategies that precisely target recyclable linkages within these robust structures offer a pathway to circularity. Here, we demonstrate an efficient chemical recycling protocol that successfully depolymerizes waste polyethylene terephthalate (PET) and cyanate ester (CE) resins into high-value small molecules, which are recovered with high purity via a streamlined separation process. Significantly, we establish a 'full-waste upcycling' paradigm based on heterogeneous waste integration, converting these recovered precursors into robust, novel cyanate ester thermosets. Unlike traditional thermosets, these fully waste-derived materials exhibit thermal shape-memory behavior, solvent-assisted chemical healing capability, and closed-loop recyclability. We elucidate a diol-mediated nucleophilic aromatic substitution (S_NAr) mechanism that facilitates the chemical recycling of these networks, enabling the regeneration of copolymers without compromising their fundamental physicochemical properties. Demonstrated as degradable electrical insulating coatings, these materials highlight a versatile and sustainable route for the circular economy of high-performance polymers.