A comparative study of epoxy resin cured with a linear diamine and a branched polyamine

The molecular topology of amine curing agents is expected to greatly affect the curing reaction and properties of the epoxy resins, yet the exact influence still remains little understood. Herein we find out two representative aliphatic amines: linear propanediamine (PDA) and branched N,N,N′,N′-tetra(3-aminopropyl)-1,3-propanediamine (TAPA), and use them to cure diglycidyl ether of bisphenol A (DGEBA). The curing reaction, dynamic mechanical properties, and thermal stability of DGEBA/PDA and DGEBA/TAPA are systematically investigated and compared. Differential scanning calorimetry (DSC) confirms TAPA and PDA have very close reactivity much higher than that of commercial Jeffamine T-403 with the branched molecular structure. The curing kinetic analysis shows TAPA causes the higher isothermal conversion at the lower temperature (e.g., 40 °C), the autocatalysis and diffusion-associated kinetics feature the isothermal reactions, and the extended Kamal model turns out to be able to well predict the curing rate. Then, the isoconversional analysis with the Vyazovkin methods demonstrates compared to PDA, TAPA leads to the lower effective activation energy at the very beginning due to its catalytic tertiary amino groups, but the reversed trend emerges in the deep-conversion stage, especially, in the glass-transition regime, owing to its flexible aliphatic molecular chains. Furthermore, the isothermal conversion at the higher temperatures is predicted from the nonisothermal experiments. Finally, dynamic mechanical analysis (DMA) shows cured DGEBA/TAPA exhibits the higher glass- and β-relaxation temperatures and crosslink density than DGEBA/PDA, and thermogravimetric analysis (TGA) reveals TAPA-cured epoxy has the excellent thermal stability with the higher char yield.

► We select two model aliphatic amines (linear PDA and branched TAPA) to cure epoxy resin (DGEBA).
► TAPA and PDA have much higher reactivity than Jeffamine T-403, and TAPA can better cure DGEBA.
► The extended Kamal model with a diffusion term can well describe the reaction rates.
► Different from linear PDA, the tertiary amine of TAPA is found to be able to catalyze the reaction.
► TAPA endows cured DGEBA with the higher crosslink density, glass temperature and char yield.