Reaction of β-Ketoester and 1,3-Diol to Access Chemically Recyclable and Mechanically Robust Poly(vinyl alcohol) Thermosets through Incorporation of β-(1,3-dioxane)ester.

The development of mechanically robust, chemically stable, and yet recyclable polymers represents an essential undertaking in the context of advancing a circular economy for plastics. Here, we introduce a novel cleavable β-(1,3-dioxane)ester (DXE) linkage, synthesized through the catalyst-free reaction of β-ketoester and 1,3-diol, to cross-link poly(vinyl alcohol) (PVA) for the formation of high-performance thermosets with inherent chemical recyclability. PVA, modified with β-ketoester groups through the transesterification reaction with excess tert-butyl acetoacetate, undergoes cross-linking reactions with the unmodified 1,3-diols within PVA itself upon thermal treatment. The cross-linking architecture improves PVA's mechanical properties, with Young's modulus and toughness that can reach up to 656 MPa and 84 MJ cm, i.e. approximately 3- and 12-fold those of linear PVA, respectively. Thermal treatment of the cross-linked PVA polymers under acid conditions leads to deconstruction of the networks, enabling the excellent recovery (>90 %) of PVA. In the absence of either thermal or acidic treatment, the cross-linked PVA maintains its dimensional stability. We show that the recovery of PVA is also possible when the treatment is performed in the presence of other plastics commonly found in recycling mixtures. Furthermore, PVA-based composites comprising carbon fibers and activated charcoal cross-linked by the DXE linkages are also shown to be recyclable with recovery of the PVA and the fillers.