Influence of disulfide bonds on the thermo-oxidative stability of aromatic epoxy-amine networks: DGEBA-AFD vitrimer versus DGEBA-DDM

This study investigates the influence of disulfide bonds, associated with covalent adaptable network behavior, on the thermal stability of aromatic epoxy-amine networks. To this end, a network synthesized by curing aromatic epoxy (DGEBA) with a disulfide-containing aromatic diamine (AFD) was aged at 160°C, and its performance was compared to a reference network composed of DGEBA cured with methylene dianiline (DDM). The degradation process was monitored using thermal (DSC), thermogravimetric (TGA), and Fourier Transform Infrared (FTIR) analyses. The results demonstrate that the DGEBA-AFD network degrades significantly slower than its DGEBA-DDM counterpart, which exhibited substantial changes in mass and glass transition temperature ( T g ). FTIR analyses confirmed these findings by revealing the accumulation of various carbonyl compounds while no oxidation of the disulfide bonds was detected. The chain scission yield per oxidation event was found to be approximately 0.47 ± 0.02 for DGEBA-DDM and nearly zero for DGEBA-AFD. We propose that internal stresses mechanically assist chain scission in DGEBA-DDM, whereas stress relaxation via disulfide exchange during curing limits this coupling in DGEBA-AFD. The results indicate that aromatic disulfide vitrimers have great potential for structural applications requiring high durability under the following conditions examined: glassy-state, network at stoichiometric and ageing at 160°C in air.