From Flower Micelles to Flower Necklaces: Self-Assembly of Dodecyl Succinate−Modified Pullulan in Aqueous Solution

Abstract Fourteen pullulan derivatives bearing dodecyl succinate side chains (PulDDS) were synthesized from seven parent pullulan samples covering wide ranges of weight-average molar mass (Mw) and degree of substitution (DS). Their micellar structures in 25 mM aqueous NaCl were characterized by SEC-MALS, light scattering, small-angle X-ray scattering (SAXS), transmission electron microscopy, and fluorescence measurements. Analysis using flower and flower-necklace models showed that low-Mw PulDDS formed unicore flower micelles, whereas high-Mw PulDDS formed multicore flower-necklace micelles. While unicore flower micelles have been reported for amphiphilic synthetic copolymers, such micelles have been much less explored for amphiphilic polysaccharide derivatives in aqueous media; here we provide a quantitative characterization based on combined scattering and fluorescence measurements. Although water is a good solvent for pullulan, low-DS samples exhibited negative second virial coefficients (A2), indicating attractive interchain interactions and no well-defined micellar structure. In contrast, high-DS samples showed positive A2 values and pronounced micellar SAXS features, consistent with repulsive interactions between looped chains.