Mechanism of Supplemental Activator and Reducing Agent Atom Transfer Radical Polymerization Mediated by Inorganic Sulfites: Experimental Measurements and Kinetic Simulations.

The mechanism of atom transfer radical polymerization (ATRP) mediated by sodium dithionite (Na2 S2 O4 ), with CuII Br2 /Me6 TREN as catalyst (Me6 TREN: tris[2-(dimethylamino)ethyl]amine)) in ethanol/water mixtures, was investigated experimentally and by kinetic simulations. A kinetic model was proposed and the rate coefficients of the relevant reactions were measured. The kinetic model was validated by the agreement between experimental and simulated results. The results indicated that the polymerization followed the SARA ATRP mechanism, with a SO2 •- radical anion derived from Na2 S2 O4 , acting as both supplemental activator (SA) of alkyl halides and reducing agent (RA) for CuII /L to regenerate the main activator CuI /L. This is similar to the reversible-deactivation radical polymerization (RDRP) procedure conducted in the presence of Cu0 . The electron transfer from SO2 •- , to either CuII Br2 /Me6 TREN or R-Br initiator, appears to follow an outer sphere electron transfer (OSET) process. The developed kinetic model was used to study the influence of targeted degree of polymerization, concentration of CuII Br2 /Me6 TREN and solubility of Na2 S2 O4 on the level of polymerization control. The presence of small amounts of water in the polymerization mixtures slightly increased the reactivity of the CuI /L complex, but markedly increased the reactivity of sulfites.