Electrolyte- and pH-Responsive Polyampholytes With Potential As Viscosity-Control Agents In Enhanced Petroleum Recovery

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Polymers and High Performance Materials


Low-charge-density amphoteric copolymers and terpolymers composed of AM, the cationic comonomer (3-acrylamidopropyl)trimethyl ammonium chloride, and amino acid derived monomers (e.g., N-acryloyl valine, N-acryloyl alanine, and N-acryloyl aspartate) have been prepared via free-radical polymerization in aqueous media. These terpolymers with random charge distributions have been compared to terpolymers of like compositions containing the anionic comonomer sodium 3-acrylamido-3-methylbutanoate. Terpolymer compositions determined by C-13- and H-1-NMR spectroscopy, terpolymer molecular weights and polydispersity indices obtained via size exclusion chromatography/multi-angle laser light scattering, and hydrodynamic dimensions determined via dynamic light scattering have allowed a direct comparison of the fundamental parameters affecting the behavioral characteristics. The solution properties of low-charge-density amphoteric copolymers and terpolymers have been studied as functions of the solution pH, ionic strength, and polymer concentration. The low-charge-density terpolymers display excellent solubility in deionized water with no phase separation. The charge-balanced terpolymers exhibit antipolyelectrolyte behavior at pH values greater than or equal to 6.5 +/- 0.2. As the solution pH decreases, these charge-balanced terpolymers become increasingly cationic because of the protonation of the anionic repeat units. The aqueous solution behavior (i.e., globule-to-coil transition at the isoelectric point in the presence of salt and globule elongation with increasing charge asymmetry) of the terpolymers in the dilute regime correlates well with that predicted by the polyampholyte solution theories. An examination of the comonomer charge density, hydrogen-bonding ability, and spacer group (e.g., the moiety separating the ionic group from the polymer chain) indicates that conformational restrictions of the sodium 3-acrylamido-3-methylbutanoate and N-acryloyl valine segments result in increased chain stiffness and higher solution viscosities in deionized water and brine solutions. On the other hand, the terpolymers with N-acryloyl alanine and N-acryloyl aspartate segments are more responsive to changes in the salt concentration. An assessment of the effects of the terpolymer structure on the viscosity under specified conditions of the ionic strength and pH from these studies should allow for rational design of optimized systems for enhanced petroleum recovery. (c) 2007 Wiley Periodicals, Inc.

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Journal of Applied Polymer Science





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