Owing to their stable three-dimensional cross-linked network and excellent mechanical and electrical insulation properties, anhydride-cured epoxy resins are widely used in dry-type transformers. 1,5,7-triazidobicyclo4.4.0deca-5-ene (TBD), a common catalyst for the ring-opening reaction of anhydrides and transesterification reactions, is widely applied in anhydride-cured epoxy resins. However, the high crystallinity of TBD results in poor compatibility with epoxy-anhydride thermosets, causing precipitation during mixing and nonuniform curing of the resin. In addition, the strong basicity of TBD induces excessive reactivity, undesirably narrowing the processing window. To overcome these limitations, a thermally latent catalyst (PTBD) was designed and synthesized. PTBD remains chemically inert at room temperature, significantly extending the processing window. Upon heating to 120 °C, PTBD dissociates into TBD, which efficiently catalyzes the transesterification reaction, thereby imparting excellent dynamic reversibility to the cured resin. This study achieves the synergistic enhancement of processability (processing window exceeding 190 min at 80 °C), mechanical performance (tensile strength up to 102.82 MPa) and degradability (complete degradation at 130 °C for 4 h) in epoxy resin systems.
Wang et al. (Mon,) studied this question.