Highly soluble and well-defined polysaccharide-based micelle in aqueous media: Decyl succinic anhydride-modified pullulan

A pullulan-based polymeric micelle was obtained by modifying pullulan with decyl succinic anhydride (PulDS) to achieve a degree of substitution ranging from 0.46 to 0.72. SEC-MALS, static and dynamic light scattering, small angle X-ray scattering (SAXS), and fluorescence measurements were performed to characterize the micelle structure of PulDS in 25 mM aqueous NaCl at two different pH of 7 and 10. The scattering and fluorescence data clearly showed that the PulDS is molecularly dispersed as flower necklace micelles in the aqueous solvents. The size distribution of the unit micelles is significantly narrower than that of the previously investigated succinic anhydride modified pullulan. The resulting unit micelle size was found to depend less on chain length and degree of substitution, but the unit flower micelle was larger at pH 7 than at pH 10, suggesting that excess ionized OH groups on the glycosidic ring provide repulsive forces between the polymer chains. These features, namely the well-defined micelle structure and high solubility in aqueous media without large aggregates, indicate potential applications in drug delivery systems and as food additives.