Partitioning of Functional Monomers in Emulsion Polymerization: Distribution of Carboxylic Acid Monomers between Water and Monomer Phases

Abstract

Carboxylic acid monomers are commonly used at low concentrations as functional additives in emulsion polymerization. Being quite water-soluble, they partition between the aqueous and polymer particle phases in complex manners. We have studied of the partitioning behavior of both acrylic (AA) and methacrylic (MAA) acids between water and a variety of individual styrene, acrylate, and methacrylate monomers. The distribution coefficients strongly depend upon the hydrogen-bond acceptor characteristics of the organic phase and the pH of the aqueous phase. AA and MAA behave similarly, but AA distributes much less strongly to the organic phase than does MAA. The logs of the distribution coefficients for both vinyl acids correlate linearly with the molar volume of the (meth)acrylate monomers, and these values decrease as the molecular weight of the monomer increases. Vinyl acid distributions to styrene monomer are nearly completely determined by the dimerization of the acids in the monomer phase and, as such, are quite sensitive to the concentration of the acid in the water phase. The effects of ionic strength and temperature are minimal for the usual emulsion polymerization reaction conditions.

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

“…A similar observation was reported for the dimerization behavior of vinyl acids. 1 Analogous conclusions can be drawn for the distribution of 2HEMA or 2HEA between water and (meth)acrylate monomer phases (Appendix F (Supporting Information)). For vinyl acid monomers, Tripathi and Sundberg 1 obtained a linear correlation between log(K d ) and the molar volume of the nonfunctional (meth)acrylate monomer for both AA and MAA.…”

“…Similar behavior was observed for the dimerization tendency of the vinyl acids in our earlier work. 1,2 From Figures 5 and 6 it can be seen that, with an increase in the polarity of the (meth)acrylate monomer, the distribution of 2HPMA increases toward the organic phase. Also, we can see that the nonlinearity in the ROH org,tot versus ROH W plots, which reflects the K value (eq 3), increases with an increase in the carbon number of the nonfunctional monomer.…”

“…While carboxylic acid groups are reported to form dimers, 1−3 hydroxy groups can form multimers via hydrogen bonding. 4 (1) where ROH O,n (n = 1, 2, 3, ...) is the concentration of the n-mer and K n (=ROH O,n /(ROH O,1 ·ROH O,n−1 )) is the equilibrium coefficient for formation of that n-mer.…”

“…For distribution of carboxylic acid functional monomers, pH can be a significant influence. 1 Carboxylic acids are weak acids and can be easily deprotonated by acid−base reactions. However, this is not the case for hydroxy functional monomers, and we would expect very minimal effects, if any, of pH on the distribution of hydroxy acrylate monomers.…”

Partitioning of monobutyl itaconate and β‐carboxyethyl acrylate between organic and water phases

“…Although these vinyl acids are partially or completely soluble in water, they will still partition to varying extents into the organic phase depending on their relative hydrophobicities. The most frequently studied acid monomers used in emulsion polymerization are itaconic acid (IA), acrylic acid (AA), methacrylic acid (MAA), and fumaric acid (FA), listed in order of their hydrophobicities.…”