A "surfactant-free" emulsion polymerization of methyl methacrylate was conducted at 80 degrees C with ammonium persulfate initiator. The water-soluble MMA-based oligomers remaining were isolated and analyzed both as-produced and after hydrolysis. NMR analysis revealed that the mole ratio of MMA repeat units to sulfate end groups in the former is 6.5. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and gel permeation chromatography both showed that the mean number of MMA repeat units comprising the extracted material is 8-9. The hydrolysis procedure rids the oligomers of their terminal groups and converts some of the methyl ester groups to acid, greatly simplifying the mass spectrum. This appears to be the first direct measurement of "surfactants" produced in situ from monomer and persulfate initiator.