Polyoxazolines with an imidazole terminal group as thermal latent curing agents for one-component epoxy resins

Official URL: https://dx.doi.org/10.1002/mame.202500468

Poly(2-oxazoline)-imidazole (POZ-Im) polymers were synthesized by one-pot termination of 2-ethyl, 2-propyl-, and 2-phenyl-2-oxazoline homopolymers with imidazole and evaluated as thermal latent curing agents (TLCs) for one-component epoxy resins (OCERs). 1H NMR, FTIR, and MALDI-TOF confirmed successful synthesis of polymers. The polymers were amorphous, exhibiting glass transition temperatures of 43°C (PEOZ-Im), 24°C (PPrOZ-Im), and 91°C (PPhOZ-Im) and showed thermal stability with onset degradation at 364°C–375°C. When incorporated into DGEBA at a fixed 5 phr Im-to-epoxy ratio, their miscibility and curing performance varied with side-chain chemistry. PPhOZ-Im was fully miscible, PPrOZ-Im was partially miscible, and PEOZ-Im formed fine dispersed domains. Dynamic DSC revealed left-limit temperatures of 91.75°C (PEOZ-Im), 94.22°C (PPhOZ-Im), and 103.28°C (PPrOZ-Im). Rheological analysis showed that PPrOZ-Im/DGEBA exhibited the longest gelation time, followed by PEOZ-Im/DGEBA and PPhOZ-Im/DGEBA. Shelf-life estimations based on viscosity doubling times and Arrhenius extrapolation indicated stability of 88 days (PPrOZ-Im/DGEBA), 34 days (PEOZ-Im/DGEBA), and 32 days (PPhOZ-Im/DGEBA) at −20°C. These results demonstrate that POZ-Im polymers provide tunable latency and curing behavior suitable for advanced composite applications.