Degradable and Recyclable Unsaturated Polyester Resin Based on the Selective Cleavage of a Hindered C-O Bond

The extensive use of unsaturated polyester resins and their composites has resulted in an increasingly aggravating problem of waste materials which are difficult to remold or degrade endowed by their highly crosslinked network. A simple and facile recovery method to fully degrade resins remains challenging so far. Here, a hindered C-O bond with a carbonyl group in the β-position of steric ester was introduced into the design and preparation of a dimethacrylate monomer and its self-polymerized unsaturated polyester resin. The obtained resin with good thermal, mechanical, and solvent-resistance properties could be efficiently degraded within 3.5 h at 90 °C at an 80% concentration of aqueous hydrazine hydrate. Selective cleavage of the hindered bond due to steric and electronic effects was activated by the prior addition of the introduced carbonyl group. Degradation products rich in benzene and carboxyl/carboxylate groups respectively could be separated readily according to the water solubility, being expected to be reused as a flocculant and other functional additives. This work provides a promising strategy for the facile recycling of unsaturated polyester resins.