Theoretical Study of Reactions between Oxygen-Centered Radicals (•OH and SO4•) and Vinyl Monomers in Aqueous Phase

In this work, reactions between industrially relevant monomers (methyl acrylate, ethyl acrylate, methyl methacrylate, vinyl acetate, and isopropenyl acetate) and oxygen-centered radicals ((OH)-O-center dot and SO4 (center dot)) are studied using a combination of quantum mechanics and transition state theory. These reactions may have a strong influence on polymer structure and properties. Thus, computational methodologies able to estimate reliably coefficients for these reactions are needed to improve the understanding of emulsion polymerization processes. In the case of reactions involving (OH)-O-center dot, the computational approach is based on the SMD-water/M06-2X/6-311++G(3df, 2p)//B3LYP/6-31+G(d, p) DFT scheme. All calculated and experimental Gibbs free energy barriers, |-|, are within 1 kcal mol(-1). In the case of reactions involving SO4 center dot, the SMD-water/M06-2X/6-311++G(3df, 2p)//CAM-B3LYP/6-31+G(d, p) DFT scheme is found to be more suitable than a similar scheme based on B3LYP. This proposed scheme works well for acrylates and methacrylates (errors within 1 kcal mol(-1)), but it may overestimate the rate coefficients of acetates reacting with SO4 center dot.