Modulation of hydrophobic interactions in associative polymers using inclusion compounds and surfactants
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abstract
We report the modulation of the solution rheology of a comblike, hydrobhobically modified alkali-soluble emulsion (HASE) associative polymer through addition of - and -cyclodextrins (CDs). The ring-shaped CDs with hydrophobic inner cores interact with the pendant macromonomer segments of the associative polymer containing hydrophobic end groups, leading to reduction in polymer solution viscosity and dynamic moduli by several orders of magnitude. We find no interactions between the CDs and the polymer backbone as substantiated by the fact that an analogous parent polymer without hydrophobes reveals no changes in the solution rheology in the presence of CDs. In contrast, the CDs encapsulate the hydrophobic groups on the associative polymer. This is confirmed by the complexation between the CD and a surfactant modified to resemble the hydrophobic macromonomer of the associative polymer as observed using 1H NMR, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). The stoichiometric ratio of complexation between the CD and the hydrophobic macromonomer is determined independently from both NMR and yield data to be 5 mol of CD/mol of hydrophobe. Interestingly, the reduction in polymer viscoelasticity in the presence of CD is reversibly recovered upon subsequent addition of different nonionic surfactants that have a higher propensity to complex with the CD than the hydrophobic segments of the HASE polymer.
