Latent Vitrimeric Reshaping of Polyesters: Capped Amines and N‑Heterocyclic Carbenes as Triggered Catalysts

We report latent catalysts for a thermally triggered transesterification in polyester vitrimers, enabling a triggered dynamic bond exchange so offering a versatile platform for reprocessable polyesters. The blocked catalysts, such as N-heterocyclic carbenes (NHC-CO₂) and the organic amine salt, triazabicyclo[4.4.0]-dec-5-ene (TBD)-methanesulfonic acid (MSA), TBD:MSA, are inactive under service conditions but active at elevated temperature or shear to enable a triggered, reversible covalent bond exchange. Catalyst activation was validated in model reactions with the salt TBD:MSA as an excellent candidate to promote transesterification at 150 °C with activation energies of 34-36 kJ·mol^-1 as probed by melt-rheology inside a vitrimer composed of poly-(2-hydroxyethyl)-acrylate (PHEA, M _n = 68.7 kDa) and dimethyl glutarate (DMG). Mechanical testing confirmed that both pristine (E = 0.03 MPa) and reprocessed (E = 0.11 MPa) samples retained tensile properties, demonstrating efficient recyclability. In contrast, the blocked N-heterocyclic carbene (NHC-CO₂) allowed an only one-time triggered activation, indicative of permanently crosslinked networks after its initial catalytic activity.