Effect of homogeneity of methanol/water/monomer mixture on the mode of polymerization of MMA: Soap-free emulsion polymerization versus dispersion polymerization

The soap-free emulsion polymerization of methyl methacrylate (MMA) was carried out with varying amount of methanol in the aqueous medium. As methanol content increased, the phase of polymerization mixture (methanol/water/monomer) changed from heterogeneous to homogeneous state and the transition occurred at 30 wt% methanol. In order to identify the mechanism of the polymerization in heterogeneous and homogeneous mixture, the properties of the prepared PMMA particles were analyzed in terms of the effects of methanol content on the conversion at 1 h, initiator concentration and polymerization temperature. With the heterogeneous mixture in the range of 0–20 wt% methanol, the polymerization product and polymerization behavior resembled those typically observed in the soap-free emulsion polymerization. On the other hand, the characteristics of the polymerization products were similar to those typically obtained in the dispersion polymerization under the homogeneous mixture ranging 40–60 wt% methanol. Thus, the homogeneity in the aqueous methanol mixture can be a critical factor in determining the polymerization modes between the soap-free emulsion and dispersion polymerization.