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Recently we reported the critical content threshold of epoxidized polybutadiene (PBep) units to induce total miscibility between poly(styrene-b-butadiene) (SB) block copolymers (BC) and uncured epoxy resin. In this work we investigate the different mechanisms involved through morphology development, depending on the content of epoxidized polybutadiene (PBep) in the initial mixture. PBep contents higher than, close below, or far below the critical threshold lead to long-range order nanostructures through reaction-induced microphase separation (RIMS) of PS block, a combination of both self-assembly and RIMS leading to vesicles or long wormlike micelles with a bilayered structure, or macroscopic phase separation, respectively. Nanoindentation was employed to identify the microphase-separated domains. Epoxy matrix can be significantly toughened for high BC contents in both prior to or through curing microphase-separated mixtures. Phase-separated domain size but also extent of interactions between them and their shape seem to be the factors contributing to toughness enhancement.

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