Preparation, curing kinetics, and properties of a novel low-volatile starlike aliphatic-polyamine curing agent for epoxy resins

A novel low-volatile starlike aliphatic polyamine with extraordinarily high –NH2 functionalities, N,N,N′,N′,N′′-penta(3-aminopropyl)-diethylenetriamine (PADT), is synthesized and its molecular structure is confirmed by the FTIR, 1H NMR and ESI-MS analysis. Then PADT is employed as the curing agent for the epoxy resin of diglycidyl ether of bisphenol A (DGEBA) and the isothermal reaction of DGEBA/PADT is systematically investigated with differential scanning calorimetry (DSC) according to the model-fitting approach and model-free advanced isoconversional method developed by Vyazovkin. The result shows that PADT possesses the high reactivity and the reaction is autocatalytic in nature. The further reaction kinetic analysis indicates that the Kamal model can well fit the reaction rate at the reaction-controlled stage, whereas the extended Kamal model with a diffusion term can provide an excellent match throughout the isothermal reaction. On the other hand, the model-free kinetic analysis reveals a strong dependence of effective activation energy, Eα, on fractional conversion, α, which could mirror the drastic change of the reaction mechanisms, in particular, the rapid drop in Eα observed in the deep-conversion regime due to the diffusion-controlled reaction kinetics. Then, a dynamic mechanical analysis (DMA) of the cured DGEBA/PADT network discloses three relaxations from the low- to high-temperature range: β (Tβ = −34.4 °C), α′ (Tα′ = 68.0 °C) and α (Tg = 144.3 °C). Moreover, compared to linear propanediamine, PADT can much increase the crosslink density and glass temperature of the cured epoxy resin. Finally, the thermogravimetric (TG) analysis reveals PADT, like propanediamine, can impart the cured epoxy resin with the excellent thermal stability with the initial decomposition temperature as high as ∼300 °C. On the basis of these experimental data, we can conclude that PADT exhibits a great potential to partially replace conventional high-volatile aliphatic-amine curing agents of low molecular weights.