Toughening of epoxy thermosets with nano‐sized or micron‐sized domains of poly(ethylene oxide)‐b‐poly(butadiene‐co‐acrylonitrile)‐b‐poly(ethylene oxide) triblock copolymers synthesized using room temperature ester coupling reaction

Abstract

AbstractPoly(ethylene oxide)‐b‐poly(butadiene‐co‐acrylonitrile)‐b‐poly(ethylene oxide) (PEO‐b‐PBN‐b–PEO) triblock copolymers with three different compositions were synthesized from poly(ethylene glycol) methyl ethers and carboxylic acid‐terminated poly(butadiene‐co‐acrylonitrile) (CTBN) by ester coupling reaction at room temperature. The PEO‐b‐PBN‐b‐PEO was incorporated into anhydride cured epoxy thermosets to improve the fracture toughness by the formation of either nano‐sized spherical micelles or micron‐sized vesicles. The polymer chemical structure was confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and gel permeation chromatography. The morphology of PEO‐b‐PBN‐b–PEO within the epoxy thermosets was investigated using a transmission electron microscope, an atomic force microscope, and a scanning electron microscope. Also, we conducted impact testing and plane‐strain fracture toughness testing to evaluate the fracture toughness in terms of the impact strength and the critical stress intensity factors (KIC) for the modified epoxy thermosets. The results revealed that all the PEO‐b‐PBN‐b‐PEO triblock copolymers are more effective in the toughening of epoxy thermoset compare to CTBN. We found that the 5 wt% PEO‐b‐PBN‐b‐PEO modified epoxy thermoset containing micron‐sized vesicles exhibited the highest KIC, which was 3.23 times as high as the KIC of pristine epoxy thermoset. Besides, the glass transition temperature remained and the tensile modulus did not reduce remarkably when the amount of PEO‐b‐PBN‐b‐PEO added into epoxy was 5 wt%.