Solubility Data of Comonomer Pairs Relevant to Aqueous-Phase Study in the Emulsion Copolymerization

In emulsion copolymerizations, the two monomers might not be equally incorporated in the copolymers. Besides copolymerization in the particles, also copolymerization in the aqueous phase can take place which affects the formation of oligomeric radicals responsible for the entry of radicals into the particles. In describing copolymerization in emulsion polymerization, one can use the normal reactivity ratios in combination with the monomer feed ratios in the phase at hand (either water phase or particle phase). Most of the research works done were focused on the feed ratio of the monomers in the particle phase. This is because of the interest in the final product. But in case of water-soluble monomers, where significant amount of polymerization already occurs in the water phase, feed ratios of monomers in the water phase have to be known. Even for less water-soluble monomers, the feed ratios in the aqueous phase are important to know, related to entry of radicals. Therefore, to calculate feed ratios in water phase, solubilities of mixtures of monomers in this phase have been measured by using a UV-Vis technique. It is shown that the solubility of one monomer is influenced by the presence of another monomer.