Most emulsion polymerization formulations include ~1-3% of a functional monomer such as acrylic, methacrylic or itaconic acid. Typically acid functional monomers are used, although for some products basic monomers such as DMAEMA (dimethyl aminoethyl methacrylate) are also used in some applications. What do all of these monomers have common? They all contain functional groups that can exist in either a neutral or charged state, depending on the pH of the latex. Acid monomers exist in an anionic form at neutral or basic pH, while basic monomers exist in a cationic form at neutral or acidic pH.
Understanding this behavior is critical to ensuring the functional monomer ends up where it is supposed to be, ideally on the surface of the particle where it is able to provide additional colloidal stability to the latex. However if the reaction conditions are not carefully selected and controlled, it is possible for much, or even most, of the functional monomer to end up in the aqueous phase as water-soluble polymer or oligomer.