Synthesis and rheological characterization of latexes stabilized by methacrylic acid containing macromonomers

A range of copolymers of methacrylic acid (MAA) macromonomers prepared by cobalt-catalyzed chain transfer and methyl methacrylate (MMA) and/or butyl acrylate (BA) was synthesized and used as a stabilizer in the emulsion polymerization of MMA. Although clear differences were observed in polymerization rates using the different MAA_x-MMA_y stabilizers, these differences were not as clearly reflected in the particle sizes nor in the rates per particle. However, a clear difference between these systems and those stabilized by MAA_x-BA_y was observed. The latter systems were all characterized by much smaller particle sizes and corresponding higher rates of polymerization. In addition, the molar masses in the latter systems were all significantly larger than those obtained in the MAA_x-MMA_y stabilized system, in which the stabilizers act as "sulfur-free" RAFT agents. Interestingly, the prepared latexes showed a range of appearances varying from "milky" to "gel-like" depending on the used stabilizer. The MAA_x-BA_y stabilized latexes had, in general, a lower viscosity and a significantly smaller (if any) yield stress than the MAA_x-MMA_y stabilized latexes, and in the latter case the rheological behavior was found to depend on the block lengths in and concentration of the stabilizer.