A water-in-oil microemulsion, water-in-cyclohexane stabilized by poly(ethylene glycol) tert-octylphenyl, was developed to prepare poly(methacrylic acid) (PMAA) particles. Up to 100%, conversion of the amphiphilic monomer, methacrylic acid (MAA), which Could not be converted to the polymer efficiently in a dioctylsulfosuccinate sodium salt/toluene microemulsion, was achieved. The viscosity-aver e molecular weight of the PMAA prepared was 1.45 X 10(5) g/mol. The effects of some polymerization parameters, including the reaction temperature and the concentrations of the initiator and the monomer, on the polymerization of MAA were investigated. The results showed that the polymerization rate of MAA was slower than that of acrylamide in the microemulsions reported in the literature. The degree of conversion increased with the initiator concentration, reaction temperature, and monomer concentration. However, the stable microemulsions became turbid during the polymerization when the reaction temperature was at 70 degrees C or at a high monomer concentration (40 wt%) The synthesized PMAA particles were spherical and had diameters in the range of similar to 50 nm. (c) 2006 Wiley Periodicals, Inc.