This paper reports the appearance of a unique foam structure and pressure-induced order-order transition (OOT) of semifluorinated block copolymers in supercritical carbon dioxide (scCO 2 ). The morphological transition of block copolymers with the fluorinated block in scCO 2 is induced by the increasing apparent volume fraction of the fluorinated domain, which is preferentially swollen with CO 2 . The poly(styrene-b-perfluorooctylethyl methacrylate) (PS-PFMA) and PS-PFMA/homoPS blend were swollen with CO 2 and showed OOT from as-cast state cylinders to lamellae at 10 MPa. However, as the pressure increased, neat PS-PFMA showed a phase transition from lamellae to a 100 nm-order ''foam'' structure instead of the typical inverted phases. On the other hand, the copolymer/ homopolymer blend was transformed into a PFMA/CO 2 -rich inverted phase such as a sponge-like bicontinuous structure.

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