The role of the ratio (PEG:PPG) of a triblock copolymer (PPG-b -PEG-b -PPG) in the cure kinetics, miscibility and thermal and mechanical properties in an epoxy matrix

The aim of this study was to evaluate the role of different poly(ethylene glycol):poly(propylene glycol) (PEG:PPG) molar ratios in a triblock copolymer in the cure kinetics, miscibility and thermal and mechanical properties in an epoxy matrix. The poly(propylene glycol)‐ block ‐poly(ethylene glycol)‐ block ‐poly(propylene glycol) (PPG‐ b ‐PEG‐ b ‐PPG) triblock copolymers used had two different molecular masses: 3300 and 2000 g mol −1 . The mass concentration of PEG in the copolymer structure played a key role in the miscibility and cure kinetics of the blend as well as in the thermal–mechanical properties. Phase separation was observed only for blends formed with the 3300 g mol −1 triblock copolymer at 20 wt%. Concerning thermal properties, the miscibility of the copolymer in the epoxy matrix reduced the T g value by 13 °C, although a 62% increase in fracture toughness ( K IC ) was observed. After the addition of PPG‐ b ‐PEG‐ b ‐PPG with 3300 g mol −1 there was a reduction in the modulus of elasticity by 8% compared to the neat matrix; no significant changes were observed in T g values for the immiscible system. The use of PPG‐ b ‐PEG‐ b ‐PPG with 2000 g mol −1 reduced the modulus of elasticity by approximately 47% and increased toughness ( K IC ) up to 43%. Finally, for the curing kinetics of all materials, the incorporation of the triblock copolymer PPG‐ b ‐PEG‐ b ‐PPG delayed the cure reaction of the DGEBA/DDM (DGEBA, diglycidyl ether of bisphenol A; DDM, Q3‐4,4′‐Diaminodiphenylmethane) system when there is miscibility and accelerated the cure reaction when it is immiscible. All experimental curing reactions could be fitted to the Kamal autocatalytic model presenting an excellent agreement with experimental data. This model was able to capture some interesting features of the addition of triblock copolymers in an epoxy resin. © 2018 Society of Chemical Industry