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Abstract. Stability of nanostructures of epoxy/acrylic triblock copolymer blends was studied. PMMA-b-PnBA-b-PMMA triblock copolymers (acrylic BCPs) having several compositions on the ratio of the block chains and the molecular weight were initially prepared and were blended with diglycidyl ether of bisphenol-A epoxy thermosets. The blends were cured using phenol novolac with tri phenyl phosphine (TPP) as the catalyst. Several nanostructures, such as spheres, cylinders, curved lamellae, were observed in the cured blends. The nanostructures were controlled by the molecular weight of the immiscible PnBA-block chain and the ratio of the PnBA in the blends. Moreover, the effect of the gel time to the nanostructures was examined by altering the trace amount of the TPP in the blends. The types of the nanostructures were almost kept irrespective of the gel time of the blends when the composition of the blends was maintained. This suggested the stability of the nanostructures of the epoxy/acrylic BCP blends made via the self-assembly mechanism, therefore a phase diagram of the cured blends was proposed.

Epoxy thermosets are applied as structural materials and adhesives in many industries, such as aerospace, automotive, and electronics, due to their excellent mechanical properties and heat/solvent resistance. In the applications, polymer blends have been studied to toughen the epoxy thermosets [1-14]. Among various toughening modifiers, block copolymers (BCPs) consisting of chemically distinct block chains have attracted attention in order to give nanostructured epoxy blends [15-40]. After the finding of the nanostructured epoxy blends with amphiphilic BCPs [15, 16], many BCPs were synthesized to study the nanostructures and the mechanical properties of the cured blends. Dean et al. [21] reported that methylenedianiline-cured DGEBA/ poly(ethylene oxide)-b-poly(butadiene) (PEO-b-PB) block copolymer blends showed a phase transition from spherical micelles to branched cylindrical micelles and finally to vesicles, as the volume fraction of the epoxy-miscible PEO block decreased. Ritzenthaler and coworkers [23, 24] studied epoxy/ ABC triblock copolymer blends. Raspberry-like nanostructures were identified in polystyrene-bpolybutadiene-b-poly(methyl methacrylate

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