A comparative study of pH-responsive polyzwitterions (PZs) with polyampholyte or polybetaine architectures was conducted with well-defined model polymer systems. Low-charge-density PZs, including ampholytic terpolymers composed of acrylamide (AM), sodium 3-acrylamido-3-methylbutanoate, and (3-acrylamidopropyl-)trimethylammonium chloride and carboxybetaine copolymers composed of AM and 3-(3-acrylamidopropyldimethylammonio)propionate, were prepared via free-radical polymerization in 0.5M NaCl to yield ter-and copolymers with random termonomer and comonomer distributions. Sodium formate was used as a chain-transfer agent during the polymerizations to eliminate the effects of the monomer feed composition on the degree of polymerization (DP) and to suppress gel effects and broadening of the molecular weight distributions. The polymer compositions were determined via 13 C-NMR spectroscopy, and the residual counterion content was determined via elemental analysis for Na ϩ and Cl Ϫ . The molecular weights (MWs) and polydispersity indices (PDIs) were determined via size exclusion chromatography/multi-angle laser light scattering (SEC-MALLS); the polymer MWs ranged from 1.4 to 1.5 ϫ 10 6 g/mol, corresponding to DPs of 1.6 -1.9 ϫ 10 4 repeat units, with all the polymers exhibiting PDIs less than or equal to 2.1. The intrinsic viscosities determined from SEC-MALLS data and the Flory-Fox relationship agreed with the intrinsic viscosities determined via low-shear dilute-solution viscometry. Data from the SEC-MALLS analysis were used to analyze the radius of gyration/molecular weight (R g -M) relationships and the Mark-Houwink-Sakurada intrinsic viscosity/ molecular weight ([]-M) relationships for the PZs. The R g -M and []-M relationships and viscometric data revealed that under size exclusion chromatography conditions, the poly[acrylamide-co-3-(3-acrylamidopropyldimethylammonio)propionate] betaine copolymers had more open, random-coil conformations and greater polymer-solvent interactions than the ampholytic poly[acrylamide-co-sodium 3-acrylamido-3-methylbutanoate-co-(3-acrylamidopropyl)-trimethylammonium chloride] terpolymers. The pH-and salt-responsive dilute-solution viscosity behavior of the PZs was examined to assess the effects of the polymer structure and composition on the solution properties. The polyampholyte terpolymers had greater solution viscosities and more pronounced stimuli-responsiveness than the polybetaine copolymers because of their stronger intramolecular interactions and increased chain stiffness.
Low‐charge‐density ampholytic terpolymers composed of acrylamide, sodium 3‐acrylamido‐3‐methylbutanoate (NaAMB), and (3‐acrylamidopropyl)trimethylammonium chloride were prepared via free‐radical polymerization in 0.5 M NaCl to yield terpolymers with random charge distributions. NaOOCH was used as a chain‐transfer agent during the polymerization to eliminate the effects of the monomer feed composition on the degree of polymerization (DP) and to suppress gel effects and broadening of the molecular weight distribution. The terpolymer compositions were obtained via 13C NMR spectroscopy, and the residual counterion content was determined via elemental analysis for Na+ and Cl−. The molecular weights (MWs) and polydispersity indices (PDIs) were determined via size exclusion chromatography/multi‐angle laser light scattering (SEC–MALLS); the terpolymer MWs ranged from 1.3–1.6 × 106 g/mol, corresponding to DPs of 1.6–1.9 × 104 repeat units, with all terpolymers exhibiting PDIs of less than 2.0. Intrinsic viscosities determined from SEC–MALLS data and the Flory–Fox relationship were compared to intrinsic viscosities determined via low‐shear dilute‐solution viscometry and were found to agree rather well. Data from the SEC–MALLS analysis were used to analyze the radius of gyration/molecular weight (Rg–M) relationships and the Mark–Houwink–Sakurada intrinsic viscosity/molecular weight ([η]–M) relationships for the terpolymers. The Rg–M and [η]–M relationships revealed that most of the terpolymers exhibited little or no excluded volume effects under size exclusion chromatography conditions. Potentiometric titration of terpolymer solutions in deionized water showed that the apparent pKa value of the poly[acrylamide‐co‐sodium 3‐acrylamido‐3‐methylbutanoate‐co‐(3‐acrylamidopropyl)trimethylammonium chloride] terpolymers increased with increasing NaAMB content in the terpolymers and increasing ratios of anionic monomer to cationic monomer at a constant terpolymer charge density. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3236–3251, 2004
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