Systematic investigation of mechanical properties and fracture toughness of epoxy networks: Role of the polyetheramine structural parameters

Polyetheramine (PEA)-modified epoxies with various types of PEAs were prepared and respective effects on characteristics of epoxy networks were studied. The used PEAs were polyethylene glycol diamine (PEG-amine) and polypropylene glycol diamine (PPG-amine) with two different molecular weights (i.e., 200 and 400 g mol^?1). According to mechanical tests, the structural parameters of PEAs played an important role in final properties of epoxy/amine systems. PEG₄₀₀-amine and PPG₂₀₀-amine had the highest and lowest effects on the properties of epoxy networks, respectively. Whereas 10 phr PEG₄₀₀-amine increased critical stress intensity factor (K_IC) and critical strain energy release rate (G_IC) of the epoxy up to 82 and 294%, the same number of PPG₂₀₀-amine chains caused to increase the K_IC and G_IC up to 11 and 34%. This discrepancy could be assigned to higher flexibility index (φ = 26.22), longer chain length (~27 atoms), and higher secondary interactions δ = 9.69 (cal cm^?3)^0.5] of PEG₄₀₀-amine in comparison with PPG₂₀₀-amine with φ = 8.08, ~10 atoms in chain, and δ = 8.98 (cal cm^?3)^0.5]. Shear yielding as a toughening mechanism was proposed based on microscopy of the crack tips. These in-depth studies could uncover underlying structure–property relationships in a relevant class of PEA-like modifiers, shedding light on the future design of top-performing homogeneous tough polymer networks. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47121.