Retrograde order–disorder transition of a semi-fluorinated block copolymer induced by supercritical carbon dioxide

Abstract

We investigated the morphological transition of poly(methyl methacrylate-b-perfluorooctylethyl methacrylate) (PMMA-b-PFMA) swollen with CO₂. CO₂ preferentially swells the fluorinated PFMA domain. While such selective swelling usually enhances the repulsive interaction between block copolymer domains, PMMA-b-PFMA exhibited an order–disorder transition in CO₂. Furthermore, a disordered phase emerged at higher pressure and lower temperature. Therefore, CO₂ swelling induced a “retrograde” order–disorder transition, where the disordered phase appears at lower temperature, despite the block copolymer neat bulk showing no ODT.