A Study of Particle Nucleation in Dispersion Copolymerization of Methyl Methacrylate

The dispersion polymerization of methyl methacrylate (MMA) and its copolymerization with the bio‐renewable monomer γ ‐methyl‐ α ‐methylene‐ γ ‐butyrolactone (MeMBL) is studied in a methanol/water mixture. The addition of MeMBL to an MMA dispersion decreases both rate and particle size (PS), while rate decreases and PS increases when the fraction of methanol in the continuous phase is increased. The differing effects of comonomer and continuous phase composition can be attributed to monomer partitioning and critical chain length ( j crit ) of the radicals formed in solution. A cobalt(II) catalytic chain transfer agent (CCTA) was used to determine a value of 20–30 monomer units for j crit in MMA dispersion polymerization. A distinct population of small particles, about one‐tenth as large as the 1–2 µm mature particles, was observed throughout the entire course of the dispersion polymerization; it is these particles, most likely aggregates of nuclei continuously generated in solution, that are swept up by the mature particles during growth.