Polymerization Initiated by the System Triethanolamine/Hydrogen Sulfite with and Without the Cooperation of Hydrogen Peroxide. 1. Polymerization of Acrylamide

Abstract

Attempts to initiate the aqueous polymerization of acrylamide, AAm, by the hydrogen sulfite/oxygen system failed. This is contrary to acrylic acid, whose monomer indeed undergoes initiation by the above initiator. Efforts to start the AAm polyreaction by hydrogen sulfite without air also yielded no polymer. It was discovered, however, that sodium pyrosulfite, PS, coupled with triethanolamine, TEA, in equimolar ratios provides a system, TEA/PS, able to generate radicals even at relatively low temperatures. On the basis of ESR investigations, these proved to be HSO₃ active centers. At three temperature (273, 278, 283 K) at an initiator (TEA/PS) molar concentration range of c ₁₍₀₎ = 0.0066–0.02 mol/dm³, and for a monomer (AAm) concentration range of c _M(0) = 0.43–1.374 mol/dm³, high rates of polymerization lying between r _p = 24.9 × 10⁻⁶ and 727.5 × 10⁻⁶ mol/dm³·s were determined. Linear relationships between lg(r _p) vs lg(c ₁₍₀₎) at constant c _M(0), and lg(r _p) vs lg(c _M(0)), at constant c ₁₍₀₎ display slopes of 1.0 and 2.5, respectively. Due to “cage effects,” the reaction yields are not very high, amounting to 70% at best. By supplementing the TEA/PS system with equimolar amounts of H₂O₂, a significant change of the mechanism of radical generation takes place. According to the ESR spectrum, the unpaired electrons appear here to be centered on the tert-amine molecules. By employing either the TEA/PS or the TEA/PS/H₂O₂ system at temperature levels of 35 or 60°C respectively, under proper conditions, the possibility exists to tailor the molecular masses of polyacrylamides in the [Mbar] _w = 1 × 10⁵ to 4 × 10⁶ g/mol range. The presence of H₂O₂ improves the reaction yield.