The entry of free radicals (formed in the aqueous phase) into polymer particles is the subject of the present work. A model has recently been developed based on the postulate that the aqueous-phase growth of the free radicals to a critical size is the rate-determining step for entry. An experimental strategy was devised to study this phenomena. Polystyrene latex with a water-insoluble inhibitor partitioned into the polymer particles was used as seed for secondary polymerization of vinyl acetate. This was done to form and isolate stable oligomers of the critical size. The presence of vinyl acetate oligomers was detected with Fourier transform infrared spectroscopy and thin-layer chromatography. Fast atom bombardment-mass spectroscopy (MS) was used to determine the molecular weights of the oligomers. Though it was not possible to determine the precise size of the vinyl acetate oligomers formed, the MS results show that the number of monomer units in the oligomers has an upper bound of 12-14. The number of units in the oligomer of critical size was estimated to be about 5-6. These experimental results are quite close to model predictions; thus this work helps in corroborating the model. Additional work is necessary to conclusively validate this model. The experimental strategy used in this work has made it possible to determine the approximate size of oligomers formed in the aqueous phase during emulsion polymerization.