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. 1. Introduction In emulsion polymerization, the water phase plays a significant role in controlling the microstructure of the latex [1]. To study the influence of water-phase kinetics in controlling the microstructure and the properties of the final latex particles, the chemical composition distribution (CCD) and molecular weight distribution (MWD) of cooligomers formed in the water phase should be determined. The CCD and MWD of the oligomers in the water phase depend on the rates of propagation in the water phase in combination with the concentrations. The ability of MALDI-ToF-MS to give the full CCD and MWD of cooligomers present in the water phase was demonstrated [2]. This information can be used in the calculation of reactivity ratios in copolymerizations. In order to calculate the reactivity ratios in the water phase, the feed ratios of monomers in this phase should also be known. In emulsion copolymerization, monomers are distributed between the different phases (monomer, water, and particle phases). The concentrations and ratios of the monomers in each phase are determined by thermodynamics [1]. Both theoretical studies and experimental studies have been done on monomer partitioning in emulsion (co)polymerizations. Two equations that have been used so far to calculate partitioning in stages II and III of an emulsion copolymerization are the