VINYL ACETATE EMULSION POLYMERIZATION KINETICS AND MECHANISM

The kinetics and mechanism of vinyl acetate emulsion polymerization was studied thoroughly by considering most of the possible variables, i.e., type of soap, concentration of soap, ionic strength, monomer volume, particle concentration, and initiator concentration. A kinetic model based on the elementary chemical reactions was presented and pictured quite clearly on the molecular level the role of each chemical species during polymerization. The expression for the rate of polymerization based on the model predicts the right dependencies of polymerization rate on all experimental variables. The integrated equations follow the polymerization curves over the whole monomer range for the whole parameter range.;The main feature of the model is that chain transfer to monomer generates a stable radical which reinitiates relatively slowly. Monomer radical can then diffuse easily out of particles. They can diffuse through several particles until they reinitiate or terminate the polymerization or attack initiator generating another initiating radical (sulfate ion radical).;The initiator concentration as a function of time was studied because there was much induced decomposition of initiator. The expression for the rate of induced decomposition of initiator derived from the kinetic model predicted exactly the dependence of the rate on experimental variables. The rate constant for induced decomposition of initiator by monomer radical was found to be 2.1 X 10('7) /mole sec which implies that the reaction is diffusion controlled.;The assumption that the chain transferred monomer radical is the stable vinyl radical,;The numbers and diameters of particles of poly (vinyl acetate) latices were determined by quasielastic laser light scattering considering the polydispersity effect. The validity of this method of particle size analysis was confirmed by comparing the results from laser light scattering to those from electron microscopy for several well characterized styrene butadiene latices.; ('O);CH(,3)--C--O--C = CH(,2),;in the kinetic model was verified by studying the isotope effect on the kinetics. The main chain transfer site of the vinyl acetate was found to be on the vinyl hydrogens (94%) instead of the acetyl hydrogens of vinyl acetate by comparing the polymerization rates and molecular weights of vinyl acetate, trideuterovinyl acetate, and vinyl trideuteroacetate run under comparable conditions.;The effect of the impurity on the kinetics was studied using one source of impurity (olefin compound) from an impure soap. It was found that the soap impurity retarded the polymerization because it underwent degradative chain transfer. The impurity radical (allylic radical) attacked the initiator raising the dependence of polymerization rate on initiator concentration.;The particle generation as a function of conversion and soap concentration (sodium lauryl ethoxylate sulfate) in unseeded polymerization was studied. It was found that at low soap concentrations, the particle numbers went through a maximum and then decreased due to the coalescence of particles; at high soap concentrations particle numbers went up steadily to 30% conversion where the separate monomer phase disappeared and stayed constant after that. The particle number was found to depend on soap concentration to the 3 power at low soap concentrations and 0.17 power at high soap concentrations.