THE EFFECT OF PHASE CHANGES ON PARTICLE SIZE IN EMULSION POLYMERIZATION

In emulsion polymerizations with the use of nonionic surfactants as the sole stabilizers, under the conditions of high monomer-to-water ratio, high polymerization temperature, low concentration of surfactants, surfactants with low HLB value, and monomers with high polarity, it was found that the polymerization may start with a multiple water-in-oil-in-water or inverted water-in-oil emulsion. These emulsions may change back to the oil-in-water emulsion during the polymerization, and thus show two-constant rate regions in the conversion curves and also a bimodality in the latex particle size distribution. The kinetics of these emulsion polymerizations do not follow the so-called ideal kinetics proposed by the Smith-Ewart theory. The introduction of less polar comonomers or anionic cosurfactants into the above polymerization systems, however, leads to the disappearance of this nonideal behavior and yields unimodally distributed latex sizes.