Imidazole- and alkyl urea-functional polymers as thermal latent curing agents for one-component epoxy resins

Official URL: https://dx.doi.org/10.1016/j.polymer.2026.129598

One-component epoxy resins (OCERs) offer simplified processing and improved handling, but achieving long-term storage stability while independently controlling cure temperature remains challenging. In this study, polymeric thermal latent curing agents (TLCs) with covalently bound imidazole and long alkyl urea functionalities were synthesized via post-polymerization modification of poly(2-ethyl-2-oxazoline) (PEOZ). A series of imidazole-functional hydrophilic homopolymers (HPs) and imidazole-/alkyl urea-functional amphiphilic copolymers (CPs) were prepared and mixed with diglycidyl ether bisphenol A (DGEBA) to systematically evaluate their dispersion quality, and the curing behavior and stability of the resulting OCERs. Differential scanning calorimetry (DSC) revealed that hydrophilic HP TLCs exhibit high cure onset temperatures (∼170–180 °C), confirming that covalent attachment of imidazole suppresses its reactivity with epoxy resin, while the hydrophilic nature of the HPs limits their miscibility with DGEBA. In contrast, amphiphilic CP TLCs exhibited lower and tunable cure temperatures because the incorporation of hydrophobic alkyl chains improved their dispersion in the nonpolar DGEBA resin, while the tunable melting temperature of the alkyl side chains provided additional control over cure onset. OCERs formulated with 5 mol% CP TLCs remained stable at −18 °C for two years, showed no curing at 60 °C for 3 h, and fully cured at 130 °C within 1 h. These results indicate that cure latency is primarily governed by polymer-epoxy miscibility and imidazole accessibility, with side-chain crystallinity providing an additional handle to modulate cure onset. Overall, this work establishes a molecular design strategy for polymeric TLCs that enables independent control over storage stability and cure kinetics in OCERs.