Separation of microphase morphologies of epoxy resins with PMMA-b-PnBA-b-PMMA acrylic triblock copolymers during curing was confirmed by in situ small-angle X-ray scattering (SAXS)/differential scanning calorimetry (DSC). Cured blends contain a variety of nano-ordered structures via self-assembly of PMMA-b-PnBA-b-PMMA upon curing; however, the mechanism was unclear. As the curing reaction proceeded, size and interdomain spacing of the micelles increased. Late in curing, the morphologies rapidly re-organized until the miscible PMMA chains were pinned in the epoxy network, which was driven by strong repulsion between the PnBA domains and the polymerized epoxy. During this process, length of the PMMA chains played an important role in disordering of phase separation; the longer PMMA chains prevented the re-organization of the neighboring micelles and the disordering of the phase-separated domains. (C) 2016 Elsevier Ltd. All rights reserved.