Complex Formation of β-Cyclodextrin- and Perfluorocarbon-Modified Water-Soluble Polymers

The complex formation has been studied by 19F NMR and viscometry of β-cyclodextrin (β-CD) and water-soluble telechelic and one-ended perfluorocarbon derivatives (C6F13 and C8F17) of poly(ethylene glycol)s (PEGs) of molecular weights of 5000 and 10000 and poly(dimethylacrylamide)s containing C8F17 pendent groups. Fluorine-19 NMR of the PEG derivatives shows CF3 resonances at about −80 and −82 ppm corresponding to monomeric and associated structures, respectively. For the case of the one-ended C6F13 PEG (M = 5000) derivatives, a formation constant on the order of 104 was determined. Addition of β-CD to this polymer leads to the formation of 1:1 β-CD−RF complexes that gives CF3 resonances that are very close to that of the monomeric RF groups. Essentially quantitative complex formation with β-CD was observed in the presence of free β-CD concentrations larger than about 10-2−10-3 M. The reduced viscosity of 1.0 wt % aqueous solutions of the telechelic PEG of MW of 10 000 containing C8F17 end groups is greatly reduced as a result of intermolecular hydrophobic association. Addition of stoichiometric β-CD completely suppresses hydrophobic association in this solution, as demonstrated by a virtually complete loss of viscosity due to association. Similar reductions in viscosity were observed for the case of poly(dimethylacrylamide) containing pendent groups. In this case a larger excess of β-CD was required to completely suppress RF association.