Synthesis of Polyacrylamide Nanogels by Intramolecular Disulfide Cross-linking

Nondegradable polyamides with protein-like properties were designed and prepared as a copolymeric hydrogel by the free-radical polymerization of acrylamide with a disulfide-containing cross-linking agent, N, N-bisacryloylcystamine. Copolyacrylamides containing pendent thiol groups (BSH) were obtained after reduction of the disulfide bonds in the hydrogel, followed by precipitation in methanol. Ellman's analysis and gel-permeation chromatography (GPC) were used to characterize the copolymer. Redissolution of the copolymer in water at very dilute concentrations, followed by air oxidation under physiological conditions (pH 7.5), resulted in nanoparticles (nanogels). The dilute concentration favored intramolecular disulfide crosslinking in the polymer chain, resulting primarily in a single-chain nanogel. Nanogel formation was confirmed and characterized using GPC, dynamic light scattering and atomic force microscopy. The size of the nanogels ranged from 20–200nm.