Spontaneous formation of giant vesicles with tunable sizes based on jellyfish-like graft copolymers
Abstract
For self-assembly studies, a series of “jellyfish-like” graft copolymers with shorter backbones and longer branch chains were adopted in this work. Chitooligosaccharide (COS), the oligomer of chitosan, was chosen as the hydrophilic short rigid backbone and poly(ε-caprolactone) (PCL) as the hydrophobic long branch chain. It was found that these special graft copolymers in 1,4-dioxane–water mixture could self-assemble into giant vesicles with diameter in the range of 0.5–54 μm. The structure parameters of COS-g-PCLs have a significant effect on their self-assembly behavior. The average number of PCL chains per COS unit and the average degree of polymerization of the PCL branch chain are the key factors for the vesicles obtained. The greater the number of PCL chains and the longer PCL chains there are on the COS unit, the larger the vesicles become. In comparison to other copolymer vesicles, the obtained giant vesicles show unusual properties. One is that the polymer vesicles undergo sequential morphology changes upon heating. With the temperature increasing, the vesicles gradually disappear in the mixed solvent. But when the temperature is reduced, the giant vesicles appear again, with a sharper size distribution compared to the original vesicles. The other property is that the polymer vesicles have a great number of amino and hydroxyl groups on their surface. These groups could be utilized for the further modification of the obtained giant vesicles, such as cross-linking of vesicles, chelating of metal ions to vesicles and so on.
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