Disk micelles from nonionic coil-coil diblock copolymers

The micellization of an almost symmetric diblock copolymer, 1,2-polybutadiene-b-poly(hexafluoropropylene oxide), with block molecular weights of 6000 and 5700, respectively, was examined in the polybutadiene-selective solvent bis(2-ethylhexyl) phthalate. Cryogenic transmission electron microscopy indicated that the copolymer self-assembled into thin disk micelles, with radii from 20 to 150 nm. Small-angle X-ray scattering measurements were effectively modeled by the form factor for a thin disk and gave a core thickness of approximately 10 nm. Dynamic light scattering measurements gave a distribution of hydrodynamic radii that was fully consistent with the dimensions inferred from microscopy and X-ray scattering. The unprecedented adoption of the flat disk morphology by a nonionic, coil-coil diblock copolymer is attributed to the extremely strong interfacial tension between the fluoropolymer core and the solvated hydrocarbon corona, as anticipated by superstrong segregation theory.