Hydrolysis and recycling of tert‑alcohol chain-extended thermoset polyurethane elastomer under moderate temperature without catalyst

The recycling of end-of-life thermoset polyurethane with covalently cross-linked structure is an urgent problem to be solved. However, the chemical recycling strongly relies on acid/base catalysts or high-temperature conditions due to its high chemical stability. To address this challenge, a bifunctional tert ‑alcohol is incorporated into the backbone of polyurethane. The steric hindrance of tert ‑alcohol substituent can promote cleavage of urethane linkages, thereby enabling efficient hydrolysis of thermoset polyurethane under catalyst-free conditions at moderate temperature. The thermoset polyurethane elastomer was prepared with commercial 2,5-dimethyl-2,5-hexanediol (DMHDO) replacing bifunctional primary alcohol as a chain extender. The results revealed that the thermoset polyurethane elastomer underwent catalyst-free hydrolysis in a water-acetone mixture at 140∼150°C. That is, its cross-linked network was nearly completely disconnected to generate linear or branched polyurethane, diphenylmethane diamine (MDA) and DMHDO. The hydrolysis mechanism was inferred based on kinetics analysis of the model compound and trapping experiment of the intermediates. Additionally, the hydrolysis products were recycled for the preparation of polyurethane elastomer. This work provides an available strategy for the hydrolysis and recycling of thermosetting polyurethane elastomers.