Soap-free emulsion polymerization (SFEP) of methyl methacrylate, butyl acrylate was conducted in water/methanol media with sodium salts of four different acidic comonomers, namely styrene sulfonic acid (NaSS), 2-acrylamide-2-methyl-1-propane sulfonic acid (NaAmps), acrylic acid (NaAA), and itaconic acid (Na 2 ita). It was found that the introduction of methanol as co-solvent (35 wt%) to the medium greatly decreases the amount of water-soluble polyelectrolyte in the cases NaAA and Na 2 ita while it does not make difference for NaSS and NaAmps. Having employed the concept of conductance dependency to the ion mobility, the onset concentration in which soluble chains were formed was detected. The addition of sulfonic-based comonomers (NaSS and NaAmps), first decreased particle size and then led to predomination of solution polymerization over SFEP. On the contrary, the incorporation of carboxylic-based comonomers (NaAA and Na 2 ita) led to increase in particle size. Moreover, the particle size results were in good qualitative agreement with the classical Smith-Ewart theory.