On semicontinuous emulsion polymerization

Semicontinuous emulsion polymerization of styrene and methyl acrylate with a feed of either monomer or monomer emulsion has been investigated. Feeding rate Rz and initial charge were varied, reaction rate Rp, degree of polymerization Pζ, number of latex particles N, and particle size distribution were measured. With both monomers Rp and Pζ are independent of Rz as long as Rz is large enough to maintain the saturation value of monomer concentration [M] in the latex particles. If [M] falls below this value a steady state is reached with monomer feed as well as with emulsion feed, Rp equals Rz, and Pζ increases with increasing Rz. Taking the Smith‐Ewart theory as a basis for calculation, the propagation rate constant kp was determined for both monomers in the steady state. Emulsion feed produces less, i.e., larger particles than monomer feed or batch polymerization, the overall charge being kept constant. Emulsion feed gives a narrower particle size distribution, and the initial rate of polymerization and N are proportional to the initial charge, if formation of new latex particles during the emulsion feed can be avoided. If not, particle size distribution is broadened and can eventually become even broader than with the other two methods.