POLYMERIZATION OF METHYL-METHACRYLATE IN TERNARY-SYSTEMS - EMULSION AND MICROEMULSION

The ternary systems containing water, methyl methacrylate (MMA), and cetyltrimethylammonium bromide (CTAB) could be continuously changed from turbid emulsions to transparent microemulsions by merely increasing the surfactant concentration. Stable PMMA latexes (16-30 nm in hydrodynamic radius) were obtained from emulsion and microemulsion polymerizations initiated by potassium persulfate (KPS). Molecular weights of PMMA were in the range of (5 to 7) x 10(6). The activation energies of the polymerizations for both systems were about the same (81 and 85 kJ mol-1). Each latex particle containing about one to two polymer chains was obtained from microemulsion polymerization of 5 wt % MMA while it was about four from emulsion polymerization at the same MMA concentration. The number of polymer chains per latex particle increased to about five for microemulsions and nine for emulsions at 9 wt % MMA. The low dependency of polymerization rate on [CTAB]0.31 and its strong dependency on [KPS]0.82 were observed for emulsion polymerizations in contrast with [CTAB]0.58 and [KPS]0.33 for microemulsion polymerizations. The possible polymerization mechanisms related to micellar nucleation, homogeneous nucleation, and monomer droplet initiation are discussed.