Aqueous solution polymerization of neutralized acrylic acid using Na ₂S₂O₅ (NH₄)₂S ₂O₈ redox pair system under atmospheric conditions

Thickening is one of the main attributes of high molecular weight poly(sodium acrylate) as a water-soluble polymer. The acrylate polymer was prepared through polymerization of NaOH-neutralized acrylic acid in aqueous solution. The reaction mixture was open to the atmosphere, providing unrestricted access to oxygen. The sodium metabisulfite/ammonium persulfate redox system was used as an initiator in the free-radical polymerization. After prevailing on a few synthetic practical problems, certain parameters affecting the reaction and product characteristics were studied. The parameters were the initiator and monomer concentration, reaction temperature, pH, and chain transfer agent (i.e., isopropanol). Assynthesized polymers were purified and evaluated viscometrically by a Brookfield viscometer (0.5 Wt% polymer solution in distilled water at 25°C). Intrinsic viscosity, [η], was also measured to calculate the viscosity average molecular weight (Mv) based on the corresponding Mark-Hawink-Sakurada equation. Changes of the isolated polymer yield, viscosity, Mv, and a couple of indirect kinetic factors including gelation/reaction times and temperature were investigated according to the mechanism and known kinetic relationships of the free-radical addition polymerization. Finally, a useful Brookfield viscosity-Mv curve was obtained and suggested to use for facile estimation of the average molecular weight of a typical poly(sodium acrylate) sample having medium to high molecular weight.