Thermally switchable catalysts for industrially relevant dynamic epoxy-anhydride composites

In response to the increasing global demand for sustainable materials and circular design strategies, this work introduces the concept of thermo-latent catalysis in thermally cured dynamic epoxy-anhydride networks. In particular, an oxalate-based quaternary ammonium salt is used. It releases 1,5,7-triazabicyclo(4.4.0)dec-5-ene (TBD) at elevated temperature and is easily accessible at high yields via a one-pot synthesis at room temperature. The salt benefits from a high thermal stability and low volatility based on the formation of an ionic pair between the protonated cation [TBDH]+ and the oxalate anion. Incorporated in a dynamic epoxy-anhydride system, the catalyst remains inactive during thermal curing, allowing processing of defect-free samples. Once activated upon heating at 190 °C for 5 min, the released TBD efficiently catalyses bond exchange reactions as confirmed by stress relaxation and reshaping experiments. Deactivation (190 °C for 90 min) and related evaporation of the liberated TBD restores static network properties and creep resistance. Bond exchange reactions can be switched ON and OFF not only in neat resins but also in glass-fibre-reinforced composites. Reprocessing experiments confirmed that welding and consolidation are only possible in the activated state, highlighting the control over bond exchange dynamics. Overall, this work demonstrates a scalable strategy for integrating dynamic behaviour into high-performance thermosets, bridging the gap between dynamic polymer chemistry and industrial applications such as fibre reinforced composites.