The effects of pH, ionic strength and concentration of the phase-transfer catalyst, tetrabutylammonium bromide, on the rate of decomposition of potassium peroxydisulfate under conditions of free-radical phase-transfer-catalysed (PTC) polymerization have been studied. The resulting rates of initiation and polymerization of methyl methacrylate under the same conditions, which reveal the effect of transfer of initiating species into the organic phase, are also presented. Low ionic strength of the aqueous phase and a pH value of 3-4 are the most favourable conditions to achieve the highest generation rate of free radicals in the organic phase under the conditions of PTC polymerization.