Interaction between Fluorocarbon End-Capped Poly(ethylene oxide) and Cyclodextrins

Abstract

Well-defined fluorocarbon end-capped poly(ethylene oxide) (PEO), known as F-HEUR, were synthesized by varying both fluorocarbon end groups and PEO chain length. Their solution properties were studied and compared with those of hydrogenated carbon end-capped PEO. Variation of the end-capped functional group from −C6F13 to −C8F17 gave rise to a significant shift in the solution rheological properties. The interaction between different cyclodextrins and these fluorocarbon derivatives of PEO was systematically examined by rheological, dynamic light scattering (DLS), isothermal titration calorimetric (ITC), and 19F NMR techniques. The viscosity of F-HEUR solution was drastically reduced in the presence of methylated β-cyclodextrin (m-βCD) due to the disruption of intermolecular hydrophobic associations, but not observed for α- and γ-cyclodextrins. The destruction of F-HEUR network structure in the presence of m-βCD was reflected by the large reduction in the plateau modulus ( ). The activation energies (Ea) determined from zero-shear viscosity decreased with m-βCD concentration until a molar ratio of 2; thereafter it remained constant. At high m-βCD concentration, subtle difference was observed for the complexes produced by −C6F13 and −C8F17 hydrophobic moieties. The inclusion complex formation between m-βCD and different fluorocarbon groups derived from ITC thermograms revealed a stoichiometry of 1:1 for C6F13 but 1:1 and 2:1 inclusion complexes for C8F17 at different m-βCD concentrations. DLS results showed a different mechanism for C6F13 and C8F17 fluorocarbon hydrophobes, which were in agreement with the results deduced from activation energies and 19F NMR spectra. A mathematic model was adopted to describe the relationship between and m-βCD concentration.