Kinetic Description of Ascorbic Acid Decomposition in Redox Initiator Systems for Polymerization Processes

The temperature dependent redox decomposition rate constants of ascorbic acid (AsAc) in aqueous solutions were quantified in the presence of ammonium iron(III) sulfate dodecahydrate (Fe-cat) and tert-butylhydroperoxide (TBHP). Decomposition rates were determined in a temperature range from 35–75 °C with respect to the component ratios. First-order kinetics were observed up to specific conversions (∼20–80%) for AsAc decomposition. The application of a flexible Weibull model provided a good and comparable description (R2 ≥ 0.992) of decomposition processes up to high AsAc conversions (96%) at all studied reaction conditions. The activation energy was determined as a function of AsAc and Fe-cat ratios (38–79 kJ mol–1). Statistical modeling facilitated the prediction of rate constants. Thus, it was possible to adjust the reaction rate of emulsion copolymerizations of vinyl acetate and Versa10 in a broad temperature range (10–70 °C) by variation of the Fe-cat content.