Recyclable thermoset hyperbranched polymers containing reversible hexahydro-s-triazine

Thermoset materials containing about 70 wt% epoxy resin are widely used in critical aerospace and wind power structures, generating enormous amounts of waste (such as offcuts and damaged, worn and disposed parts) that affect both the environment and the sustainable development of human society. Owing to their irreversible crosslinked networks, thermoset materials pose major challenges for rapid degradation and high-efficiency recycling. Here we report the synthesis of thermoset hyperbranched polymers (HER-HTn) containing a reversible heterocyclic structure (hexahydro-s-triazine) that can be degraded under relatively mild conditions. The cured HER-HTn exhibit excellent mechanical and thermal properties, as well as rapid degradability in more environmentally friendly phosphoric acid solutions. Controlled degradation experiments show that the cured HER-HTn can be completely digested at relatively low temperatures (90 °C) in a short period (2 h) to recover 2-aminobenzyl alcohol at a high recycling efficiency (85.1%). The recovered 2-aminobenzyl alcohol can then be used to produce the initial hexahydro-s-triazine monomer, which demonstrates the reversibility of the hexahydro-s-triazine structure and recoverability of the thermoset hyperbranched polymers. This investigation provides a method for the synthesis of a degradable thermoset matrix and the cyclic use of high-value materials in the thermoset and its composites.