Self-association of water-soluble fluorinated diblock copolymers in solutions

The self-association of the fluorinated diblock copolymer, poly(methacrylic acid)–block–poly(perfluorooctylethyl methacrylate) (PMAA-b-PFMA), in water has been investigated by light scattering, potentiometry, atomic force microscopy, and transmission electron microscopy. The size of the polymer micelles increases, as the degree of dissociation of the PMAA blocks increases. Since the charged PMAA block takes the stretched structure, PMAA-b-PFMA can easily form large micelles due to the low steric hindrance of PMAA blocks. Addition of NaCl shielded electrostatic repulsion in the PMAA chain and induced the formation of smaller micelles than water without NaCl did because of the bulky structure of the PMAA chain in the shell of the micelles. The micelle of PMAA-b-PFMA in ethanol is larger than that of poly(t-butyl methacrylate)–block–poly(perfluorooctylethyl methacrylate) (PtBMA-b-PFMA) in ethanol as a result of the higher steric hindrance of the PtBMA block. The dimensions of the core and shell of the micelles were estimated. The micelle of PMAA-b-PFMA in water possesses a rather thick shell and a large volume per molecule, consistent with the extended PMAA chain. On the other hand, the shell of the micelle in an ethanol solution of PtBMA-b-PFMA is thin but has a large surface area. Facts are consistent with the shrunk structure of the PtBMA block in poor solvent.