Micellar Structure of a Hydrophobically Modified Pullulan in an Aqueous Solution

Narrow distribution pullulan (PUL) samples with different degrees of polymerization (=142-4540) were reacted with octenyl succinic anhydride (OSA) to obtain a hydrophobically modified pullulan (PUL-OSA). The micellar structure formed by PUL-OSA in 0.05 M aqueous NaCl was investigated by small-angle X-ray scattering (SAXS) and fluorescence from pyrene solubilized in the aqueous PUL-OSA solution. SAXS profiles for PUL-OSA solutions were fitted using the flower necklace model consisting of nc unit flower micelles, and nc values estimated by SAXS were almost consistent with results from fluorescence decay of the solubilized pyrene. The micellar structure of PUL-OSA characterized by SAXS and fluorescence was considerably different from that of the alternating copolymer of sodium maleate and dodecyl vinyl ether, P(MAL/C12), an amphiphilic vinyl polyelectrolyte. The flower necklace of PUL-OSA has smaller unit flower micelles and a larger global dimension than the flower necklace of P(MAL/C12), probably due to differences in the hydrophobic alkyl chain length and the bulkiness of the backbone chain.