Aqueous polysaccharide associations mediated by β-cyclodextrin polymers

Macromolecular assemblies were elaborated by mixing in water hydrophobically modified dextrans (MDCn) and P-cyclodextrin polymers (p beta CD) interacting by inclusion complexation between the hydrophobic moieties of MDCn and the P-cyclodextrin cavities of p beta CD. Dextrans have been modified by grafting alkyl groups (C-n) of varying chain lengths (n = 8-16) and grafting ratio (3-6 mol%). Different p beta CD polymers were synthesized by polycondensation of P-cyclodextrin and epichlorohydrin. The polymer-polymer interactions have been studied by fluorimetry, isothermal titration microcalorimetry, phase diagrams, and viscosimetry. The viscoelastic properties of the temporary networks (in the semidilute range) have been studied by rheology. The interaction mechanisms between the MDCn and p beta CD can be understood taking into account the strength of the interaction between the alkyl group and the beta-cyclodextrin cavity (mainly controlled by the alkyl chain length), the density of junctions between the chains (depending on the alkyl grafting density and the p beta CD molecular weight), and additional cooperative effect (arising for high alkyl grafting density).