Semicontinuous heterophase polymerization was used to copolymerize methyl methacrylate (MMA) with reactive surfactant HITENOL BC10 (HBC10) at 60 A degrees C using sodium dodecyl sulfate as pre-stabilizing agent and potassium persulfate as initiator. The mixture of MMA and HBC10 was added at constant rate in continuous mode varying the MMA/HBC10 ratio. High-polymerization rates were observed, decreasing as the MMA/HBC10 ratio decreased. Latexes with polymer content near 20% and polymer to surfactant (P/S) weight ratios between 5 and 15 were obtained. Particle sizes distribution were bimodal in all cases with a tendency to be monomodal as HBC10 concentration increased which was ascribed to enhanced particle stabilization by the presence of HBC10. The average particle diameters at the end of polymerizations for the first and second populations were around 10 and 50 nm, respectively. Very high average molecular weights were observed (1.4 x 10(6) a parts per thousand currency sign M (w) a parts per thousand currency sign 2.1 x 10(6) g/mol), which decreased when HBC10 concentration increased. The corresponding polydispersity indexes (M (w) /M (n) ) were in the range of 1.45-2.24.