The invention relates to a method for prepg. microgel particles according to a method of controlled radical polymn. in an aq. dispersion using particular control agents of the nitroxide type. Use in the biomedical field, and in the field of agrochem., cosmetics, surface coatings. Dispersions of microgel particulates with particle size ≤100 nm are manufd. in the absence of surfactants by (a) polymn. of ≥1 monomer in the presence of R2OCOCR1R3ON(CMe3)CH(CMe3)P(:O)(OEt)2or Z[CH(CH2CR1R3CO2R2)ON(CMe3)CH(CMe3)P(:O)(OEt)2]n [R1, R3 = C1-3 alkyl, R2 = H, C1-8 alkyl, Ph, alkali metal, or NH4, Z = arom. group or Z1[XC(O)]n, Z1 = polyfunctional group, X = O, N having a carbon-contg. group or H, or S, n ≥ 2] in an aq. media, (b) polymn. of a vinyl monomer different from the monomer in step (a) in the reaction medium contg. the macroinitiator from step (a), and (c) polymn. of a crosslinking monomer in the reaction medium from step (b), with ≥1 of the monomers from steps (a), (b), and (c) having ≥1 group selected from CO2H, SO3H, NH4, ethylene oxide, amino, and amide, with the group optionally existing in the presence of a salt. [on SciFinder(R)]