A MASS-SPECTROMETRIC INVESTIGATION OF THE WATER-SOLUBLE OLIGOMERS REMAINING AFTER THE EMULSION POLYMERIZATION OF METHYL-METHACRYLATE

A ''surfactant-free'' emulsion polymerization of methyl methacrylate w as conducted at 80 degrees C with ammonium persulfate initiator. The w ater-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 s pectrometry and gel permeation chromatography both showed that the mea n 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 simplify ing the mass spectrum. This appears to be the first direct measurement of ''surfactants'' produced in situ from monomer and persulfate initi ator. (C) 1995 John Wiley & Sons, Inc.