Synthesis of amphiphilic block copolymers based on tert-butyl methacrylate and 2-(N-methylperfluorobutanesulfonamido)ethyl methacrylate and its behavior in water

Di- and triblock copolymers of tert-butyl methacrylate (tBMA) and 2-(N-methylperfluorobutanesulfonamido)ethyl methacrylate (FMA) were synthesized by sequential anionic polymerization. These polymers were characterized by size-exclusion chromatography and H-1 and F-19 NMR spectroscopy. The microphase separation of bulk samples was studied by atomic force microscopy and small-angle X-ray scattering. Thermal annealing of the block copolymers at 200 degreesC yielded inter- and intramolecular anhydrides due to the splitting of the ester having tert-butyl groups connected with isobutene formation. This conversion was followed by time-resolved Fourier transform infrared (FT-IR) spectroscopy. The anhydrides can be transformed into the sodium salt of methacrylic acid units in 1 N NaOH under reflux. The thermal ester splitting of the tBMA block at 200 degreesC did not influence the FMA block. The obtained block copolymers were soluble in water when the FMA content was less than 10 mol %. The behavior of these solutions was studied by various experimental methods. The critical micelle concentration was obtained by surface tension measurements. The micelle dimensions were determined by dynamic light scattering. The size and inner structure of the micelles were investigated by small-angle X-ray scattering and could also be observed by transmission electron microscopy after transfer of the diluted solutions onto carbon films. Typical polyelectrolyte effects were observed by viscosity measurements for PtBMA only. For block copolymers the aggregation behavior is dominating even at very low concentrations.