Partitioning of Functional Monomers in Emulsion Polymerization: Distribution of Hydroxy (Meth)acrylate Monomers between Water and Single and Multimonomer Systems

We have studied the partitioning behavior of a series of hydroxy acrylate monomers (2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate) between water and a variety of styrene, acrylate, and methacrylate homo-, co-, and termonomer phases. The distribution coefficients for both single and multicomponent systems strongly depend upon the hydrogen bond acceptor characteristics of the organic phase, but not on the pH of the aqueous phase. These measured distribution coefficients for multicomponent monomer systems can be adequately predicted by applying an appropriate "mixing rule" to the distribution and dimerization coefficients obtained from single monomer systems. The logarithms of these binary coefficients correlate linearly with the molar volume of the (meth)acrylate monomer phase. Hydroxy acrylate monomers are subject to dimerization and multimer formation in organic phases and those equilibrium coefficients are roughly equal for the three monomers studied here, despite their wide difference in polarities. When vinyl acid and hydroxy acrylate monomers are used simultaneously, the distribution coefficients for both monomers increase. These effects depend upon the polarity of the organic phase, the polarities of both functional monomers, and the amount of the functional monomers used in the system. We found minor effects of temperature and negligible effects of ionic strength for the usual emulsion polymerization conditions.