Water-solvent regulation on complete hydrolysis of thermosetting polyester and complete separation of degradation products

As one of the largest productions of thermosetting plastics, unsaturated polyester resin (UPR) is difficult to be effectively chemcycled after it is discarded due to its dense network structure. Herein, we demonstrate a mild method for efficient alkaline hydrolysis of UPR into useful feedstocks in mixed solvents of polar aprotic solvent and a small amount of H2O by utilizing the fragmentation effect of the solvent on the UPR and the swelling effect of H2O on the subsequent partially hydrolyzed UPR respectively. The mixed solvents also play a key role in the aggregation and solubility of the degradation products. It is worth noting that the tetrahydrofuran (THF)-H2O system achieved 100 % separation of degradation products in an energy-efficient way taking advantage of the insolubility of the carboxylate-containing products in THF and the low boiling point of THF. The participation of non-reactive mixed solvents greatly promotes both the degradation and the separation process of thermosetting polymers.