Toward an understanding of the role of water-soluble oligomers in the emulsion polymerization of styrene-butadiene-acrylic acid. Separation and characterization of the water-soluble oligomers

A series of techniques were developed to quantitatively characterize the free water-soluble oligomers found in the aqueous phase in a model styrene/butadiene/acrylic acid (St/Bu/AA) batch emulsion terpolymerization process. Particular attention was paid to the early stages of the polymerization. Ultracentrifugation was used to accomplish the separation of the aqueous phase from the particle phase. H-1 NMR, aqueous phase GPC, and GC techniques were used to determine the oligomer concentration as well as their composition and them surfactant concentration in the aqueous phase, the oligomer molecular weight, and the acrylic acid monomer conversion, respectively. The results were related to the overall conversion and the number of particles as a function of conversion. The oligomer concentration vs conversion curves for the model system show a maximum at around 12% conversion. However, the position of this maximum with respect to conversion is related to the surfactant concentration. The sharp decrease in the oligomer concentration after micelles disappeared, and the decrease in the number of particles was considered to have resulted from a strong interaction of these oligomers, which are rich in St and Bu units, with the polymer of the latex particle surface. Increasing the AA concentration in the recipe increased the water-soluble oligomer concentration and the number of particles, thereby increasing the rate of polymerization.