Synthesis of Poly(Sodium Acrylate) Nanogels Via Semicontinuous Inverse Heterophase Polymerization

The synthesis of superabsorbent poly(sodium acrylate) by semicontinuous inverse heterophase polymerization is reported here. In this process, an aqueous solution of sodium acrylate, initiator, and a cross-linking agent is dosed at a controlled rate over an organic solution containing surfactant. These nanogels exhibit a large swelling ratio (compared to the dry nanoparticles synthesized by inverse microemulsion polymerization), which increase to some extent with temperature, but then at ca. 30 degrees C, they de-swell slightly. Possible explanations to this behavior are the release of residual stresses originated during nanoparticles purification and drying, the association-dissociation of ionic clusters, and the thermoelastic inversion point of the elastic modulus of the nanogels.