A combination of fracture mechanisms including shear deformation, crack tip blunting, and matrix ductility enhancement contributed toward helped enhance the toughness. The specific side-groups of eSBS46-AEP containing secondary amines and ternary amines increased the reactivity to epoxy matrices. Various measurements including transmission electron microscopy (TEM), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), and measuring stress field factor (KIC) analysis were employed to investigate the morphology, fracture graph, storage modulus, glass transition temperature (Tg), and fracture toughness of the epoxy thermosets containing these BCPs. These findings were compared with data obtained from the same epoxy thermoset formulation containing the eSBS46. At 5 wt% loading of this BCP material, the fracture toughness was improved by 51% over the neat epoxy. As a result of the oxirane ring-opening achieved (to a conversion degree of 10 mol%) by reaction with AEP, the nanostructured morphology was converted from spherical micelles in the case of eSBS46 to branched wormlike micelles for eSBS46-AEP. In the present work, a novel block copolymer was obtained from a commercial poly(styrene-block-butadiene-block-styrene) (SBS) triblock copolymer precursor by a two-step process including reaction with hydrogen peroxide in a water/dichloroethane biphasic system to achieve an epoxidized derivative with a 46 mol% degree of epoxidation (thus denoted as eSBS46), which was then followed by reaction with 1-(2-aminoethyl)piperazine (AEP, thus yielding eSBS46-AEP) as a reactive functional group that was incorporated to prepare nanostructured epoxy thermosetting blends. Block copolymers (BCPs) have stimulated widespread research interest due to their applications as facile templates in the fabrication of optimized thermosets with micro– or nanostructured morphologies.
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