Kinetics of emulsion copolymerization with acrylic acids

A kinetic model is presented that describes the reaction behavior of emulsion copolymerization systems where significant polymerization occurs in both the particle and aqueous phases. Equations for predicting aqueous-phase free-radical concentrations and aqueous-phase and particle-phase reaction rates are developed. A method for estimating the radical entry rate coefficient is also presented. The model is applied to two seeded carboxylated emulsion copolymerization systems, acrylic acid-styrene and methacrylic acid-styrene. Both experimental and predicted results reveal that the reaction behavior is greatly affected by the type of acid monomer, partition of monomer between the various phase, and locus of polymerization. The mechanism for the acrylic acid-styrene system is more complicated than that for the methacrylic acid-styrene system. Evidence suggests that the primary reaction locus in the acrylic acid-styrene system shifts from the particles to the aqueous phase after the hydrophobic monomer, styrene, has been consumed.