Stimuli-responsive polyampholytes based on acrylamide and amino acid derived N-substituted acryoyl monomers: Synthesis, characterization, and aqueous solution behavior ofpH- and salt-responsive model systems

The fundamental structure-property-performance relationships of stimuli-responsive polyampholytes synthesized from acrylamido monomers were studied utilizing well-defined model systems. In order to elucidate significant comparisons between polyampholytes of varying compositions, it was necessary to prepare model terpolymers with random charge distributions, homogeneous compositions, and well-defined molecular weights (MW) and molecular weight distributions (MWDs). Thus, low-charge-density amphoteric copolymers and terpolymers composed of acrylamide (AM), (3-acrylamidopropyl)trimethyl ammonium chloride (APTAC), and the amino acid derived monomers (e.g. N-acryloyl valine (AVA), N-acryloyl alanine (AAL), and N-acryloyl aspartate (AAS)) were prepared via free-radical polymerization in aqueous media to yield terpolymers with random charge distributions and homogeneous compositions. Sodium formate (NaOOCH) was employed as a chain transfer agent during the polymerization to suppress gel effects and broadening of the MWD. Terpolymer compositions were determined by 13C and 1H NMR spectroscopy. Terpolymer MWs and polydispersity indices (PDIs) were obtained via size exclusion chromatography/multi-angle laser light scattering (SEC-MALLS) while hydrodynamic diameters were obtained via dynamic light scattering. Intrinsic viscosities determined by SEC-MALLS utilizing the Flory-Fox equation were found to agree with intrinsic viscosities measured via dilute solution viscometry. The data from SEC-MALLS experiments allowed for the comparison of radius of gyration-MW (Rg-M) relationships and the Mark-Houwink-Sakurada intrinsic viscosity-MW ([eta]-M) relationships for terpolymers and provided information regarding the dependence of macromolecular conformation and solvation on terpolymer composition. The Rg-M and [eta]-M relationships indicated little or no excluded volume effects under SEC conditions (expected near theta conditions of the measurements).; The pH- and salt-responsive dilute solution viscosity behavior of the low-chargedensity amphoteric copolymers and terpolymers has been examined to assess the effects of polymer structure and composition on solution properties. The low-charge-density terpolymers display excellent solubility in deionized (DI) water with no phase separation. The charge-balanced terpolymers exhibit antipolyelectrolyte behavior at pH values ≥ (6.5 +/- 0.2). (Abstract shortened by UMI.)...