Complex formation of β-cyclodextrin- and perfluorocarbon-modified water-soluble polymers

The complex formation has been studied by F-19 NMR and viscometry of beta-cyclodextrin (beta-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 C3F13 PEG (M = 5000) derivatives, a formation constant on the order of 10(4) was determined. Addition of beta-CD to this polymer leads to the formation of 1:1 beta-CD-RF complexes that gives CF3 resonances that are very close to that of the monomeric RF groups. Essentially quantitative complex formation with beta-CD was observed in the presence of free beta-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 beta-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 beta-CD was required to completely suppress RF association.