No abstract

The seeded semibatch emulsion polymerization of n-butyl acrylate was investigated using potassium persulfate as initiator at 75 °C. The effect of initiator concentration and monomer feeding time (feed flow rate) on the kinetics, fraction of gel, molecular weight distributions, and level of branches were studied. It was found that the amount of gel formed was independent of initiator concentration and monomer feed flow rate if the process proceeded under starved conditions. On the other hand, the higher the initiator concentration and the feeding times, the higher the level of branches but the lower the molecular weights. A high level of branches was found, which was attributed to intramolecular transfer to polymer or backbiting.

A mathematical model for the computation of kinetics, branching frequency, sol molecular weight distribution, and gel fraction for the seeded semicontinuous emulsion polymerization of n-BA is presented. The model incorporates mechanistic features that have been found to play an important role in the polymerization of n-BA, such as the intramolecular transfer to polymer, so-called backbiting, and the low reactivity of the tertiary radicals resulting from such a reaction. Model parameters for which values are not available in the literature were obtained by fitting the model predictions to the kinetic data and structural properties of the polymer (fraction of gel, sol molecular weight distribution, and level of branches) gathered in seeded semicontinuous emulsion polymerizations of n-BA carried out at 75 °C with potassium persulfate as the initiator. The model fits all of these experimental data quite well.