Curing of epoxy resins with in situ-generated substituted ureas

An epoxy resin based on bisphenol‐A diglycidylether (DGEBA) was cured with a substituted urea generated in situ from the reaction of piperidine with an equivalent amount of toluenediisocyanate (TDI). Curing at 100°C or higher temperatures, during 24 h, led to a complete conversion of epoxy groups and the appearance of aliphatic ethers and oxazolidone rings as revealed by IR spectra. The epoxy conversion was proportional to the oxazolidone concentration. The reaction heat was (−ΔH) = 61 kJ/eq. The maximum Tg was 102°C, e.g., the same value as the one obtained with piperidine alone. Thus, the cure with the substituted urea leads to a similar network but has the following advantages: increase in the latency of the initial formulation, absence of secondary amine volatilization (reproducible curing schedule), and decrease in the reaction heat per epoxy equivalent.