Multirecyclable, Self-Healable, Chemically Degradable, and High-Strength Epoxy Vitrimers Containing Tailorable Imine Bonds

Epoxy (EP) vitrimers are considered the ideal substitutions for conventional thermosetting EPs due to their sustainability. However, for industrial applications, the high strength of vitrimers usually contradicts a high recovery ratio. Herein, we synthesized a series of hardeners containing imine bonds via the reaction of a Schiff base between p-phenylenediamine and vanillin, which were then used to prepare EP vitrimers with various imine bond contents according to stoichiometric ratios. EP vitrimers exhibited a tensile strength of at least 54.9 MPa, and all of the vitrimers can be self-healed and reprocessed at high temperatures. Moreover, with the increase of imine bond content, the activation energy (E_a) and topology freezing transition temperature (T_v) of the vitrimers decreased, leading to the improved recovery ratio. The optimal comprehensive properties of the EP vitrimer were achieved for EPV-VP-1.5, with a T_g of 132.7 °C, a tensile strength of 82.4 MPa, an elongation at break of 5.5%, and a recovery ratio of 91.5% in the first recycling process. Even after recycling three times, a tensile strength of 62.8 MPa was retained. Moreover, all EP vitrimers can be dissolved completely in 0.5 mol L^-1 HCl with DMF solutions at 50 °C after 2 days. Therefore, this work demonstrated a strategy to prepare EP vitrimers with both high strength and a high recovery ratio.