Stability of carboxylated poly(butyl acrylate) latices during semibatch emulsion polymerization

The stability of latex particles in the semibatch emulsion polymerization of butyl acrylate (BA) in the presence of 0-10% acrylic acid (AA) was investigated. The amount of coagulum (i.e., large flocs caused by intensive coagulation) can be greatly reduced by an increase in the concentration of sodium lauryl sulfate (SLS) in the monomer emulsion feed. On the other hand, increasing the concentration of SLS in the initial reactor charge can result in an increase in the percentage of the particle volume change (i.e., a measure of the degree of limited flocculation) later in the process. Both the scrap and percentage of the particle volume change increase with an increase in the electrolyte concentration. Both the coagulation and secondary nucleation process can result in a significant deviation from the Novak model. Experimental data also show that latex particles comprising pure BA can lose their stability rapidly at higher total solids content because of the crowding effect. Incorporation of only 5% AA into the emulsion polymers greatly improves the latex stability. (C) 1996 John Wiley & Sons, Inc.