Semibatch Surfactant-Free Emulsion Polymerization of Butyl Acrylate

Abstract

The latex particles can maintain an appreciable stability by the limited flocculation process during the semibatch surfactant-free emulsion polymerization of butyl acrylate, especially at higher total solids content. Intensive agitation (e.g., 800 rpm in a 1-liter reactor) can result in a significant amount of coagulum in addition to limited flocculation. At a common reaction time, the latex particle size increases with an increase in the monomer feed rate. A large amount of scrap is formed for the run with the highest monomer feed rate. At any time during polymerization, the particle size first increases to a maximum and then decreases with an increase in the initiator concentration. The run with the lowest level of initiator shows the worst latex stability because there is an insufficient supply of sulfate end-groups to stabilize the growing particles. However, a significant amount of coagulum is observed for the run with a higher level of initiator due to the ionic strength effect. The optimum latex stability occurs at a point close to an initiator level of 0.19%. The effect of buffer on the latex particle size and stability is significant, again, due to the ionic strength effect. The critical flocculation concentration is 0.45 N NaCl.