Synthesis and characterization of hydrophobically modified twin-tailed associative polymers using micellar polymerization: Terpolymers based on methacrylamide, acrylic acid, and N,N-dialkylacrylamides

Geoffrey Lawrence Smith


The overall goal of this research has been to develop twin-tailed hydrophobically modified water-soluble polymer systems which exhibit responsive associative thickening behavior. These twin-tailed amphiphilic polymer systems have been synthesized and their tendency to form predominantly intermolecular associations has been evaluated. Also, their capacity to thicken aqueous solutions under different conditions of pH and surfactant concentration has also been examined. Series of terpolymers containing acrylic acid, methacrylamide and a N,N-dialkylacrylamide, twin-tailed hydrophobic monomer (DiC6 AM, DiC8 AM or DiC 10 AM have been synthesized using micellar polymerization methods. Characterization of these polymer systems was performed using light scattering, viscometry, and fluorescence methods. Changes in the energy transfer efficiency and viscosity behavior as a function of pH are consistent with a concentration-dependent transition from closed to open associations. The interactions of these terpolymers, with different surfactants is also investigated. These surfactants include a similarly charged surfactant (SDS), an oppositely charged surfactant (CTAB), and a nonionic surfactant (Triton X-100). Viscosity measurements performed on the DiC 6 AM and DiC8 AM indicate similar noninteraction with SDS, extreme interaction and gelation with CTAB, and hemimicelle formation followed by polymer hydrophobe solubilization with the Triton X-100. Surface tension measurements confirm this interaction by indicating the presence of a critical aggregation concentration. Fluorescence measurements performed on a dansyl labed DiC 10 Am terpolymer in the presence of increasing amounts of each of the three different surfactants indicate that CTAB interacts the most with the polymer followed by Triton X-100 and SDS, confirming viscosity and surface tension results. A similar series of terpolymers composed of acrylic acid, methacrylamide and a more hydrophobic, twin-tailed N,N-dialklyacrylamide monomer (DiC 12 AM, DiC14 AM, or DiC16 AM) has also been synthesized using micellar polymerization methods. Results indicate that a critical pH between 6.5 and 9 for each terpolymer, is required to cause network disruption and chain reorganization. Finally, fluorescence energy transfer measurements performed on the DiC 12 AM terpolymer indicated the onset of association occurring at ∼0.04 g/dl. (Abstract shortened by UMI.)