Dual-responsive epoxy thermosets with controlled degradation and high performance based on serial connection of double dynamic bonds

Covalent adaptable networks relying on dynamic cross-links have been developed to make the conventional thermosets degradable and reprocessable, but the greater challenge lies in how to overcome the trade-off between excellent degradability and mechanical properties. It remains a formidable challenge to achieve complete degradation of high mechanical materials (such as epoxy) especially at more moderate conditions. Herein, dual-responsive epoxy thermosets that were serially cross-linked by double dynamic bonds of disulfide bonds and cation-π interactions were prepared from diglycidyl ether of bisphenol A (DGEBA), dithiodianiline (DTDA), N-expoxypropane-indole (EIN) and MgCl2. The dual-responsive epoxy exhibited moderate mechanical properties with the tensile strength of 55 MPa, while the glass transition temperature (Tg) was 85 °C. In addition, the dual-responsive epoxy could be degraded by either DTT or PPi, due to the thiol-disulfide oxidation/reduction reaction and the complexation reaction of PPi and Mg2+. Furthermore, the degradation times could be controlled from <100 to 2700 min with optimal conditions by varying the concentration of reactive molecules and temperature. Meanwhile, the dual-responsive epoxy also exhibited excellent reprocessing properties. The dual-responsive dynamic epoxy thermoset is expected to be useful for coatings, adhesives, and matrix polymers of composites that require controlled degradation and recyclability.