Manipulation of hydrophobic interactions in associative polymers using cyclodextrin and enzyme

Abstract

We examine a new approach to reversibly modulate hydrophobic interactions in associative polymers using cyclodextrins (CD) and enzymes that cause scission of the α-1, 4 linkages in cyclodextrins. The associative polymers have a comb-like structure with pendant hydrophobic groups randomly attached to the polymer backbone. The intermolecular interaction between hydrophobic groups forms a transient network resulting in thickening of solutions containing the polymer. The CDs, doughnut-shaped cyclic polysaccharides, encapsulate the hydrophobes within their hydrophobic cavity and eliminate hydrophobic interactions. This results in several orders of magnitude reduction in solution viscosity and other viscoelastic properties. Subsequent degradation of the CDs by enzymes restores the hydrophobic interactions and the original rheological properties. A rheokinetic model is developed to describe the kinetics of the enzymatic reactions. The model accounts for equilibrium between the CD bound to the hydrophobes and free CD in solution and assumes the enzyme hydrolyzes only the free CD in the solution, which causes the release of the bound CDs in order to maintain equilibrium. The reaction is assumed to follow Michaelis Menten kinetics and the kinetic parameters are determined by tracking the changes in the viscoelastic properties of the polymer solution during the enzymatic scission of CD. The effects of enzyme concentration, polymer concentration and temperature on the rate of recovery of the original rheological properties are experimentally determined, and used to validate the trends of the rheokinetic model.