Micelle-like association of polysaccharides with hydrophobic end groups

• Dextran derivatives with hydrophobic end groups were prepared by reductive amination.
• Nano-scaled micelle-like aggregates are formed in aqueous solutions.
• Attachment of cationic groups to dextran main chain preserves the aggregation capacity of end-modified polymers.
• Crosslinking of dextran micelle shell stabilizes the micelles against dilution.

New dextran derivatives with hydrophobic end groups were synthesized by reductive amination of dextran chain ends, followed by chemical modification of the dextran main chain by attachment of cationic groups and/or by crosslinking. Properties of the aggregates formed by hydrophobic association of the end groups were studied by fluorescence, dynamic light scattering, atomic force microscopy and transmission electron microscopy and depended on the length of the dextran chain (6, 10, 25 kDa) and the hydrophobicity of the end group (alkyl, dialkyl, bile acid). All neutral derivatives were able to form micelle-like aggregates above a critical aggregation concentration (0.008–0.159 g/dL). Polarity of the micelle hydrophobic core was close to or lower than that of neutral low molecular surfactants (polarity parameter I1/I3 ≈ 0.8–1.13), aggregation number was 20–30 and hydrodynamic radius 20–30 nm. Attachment of cationic groups to the dextran main chain increased critical aggregation concentration and core polarity, but cationic polymeric surfactants with good association ability could be obtained by an appropriate choice of the content and hydrophobicity of the cationic groups. Cross-linking of the micelle shell with divinylsulfone increased micelle stability to dilution.