Atactic poly(methyl methacrylate) (a-PMMA) nano-particles were prepared in three-component microemulsions using the cationic surfactant cetyltrimethylammonium bromide. To analyze the thermal history, the sub-T-g annealed sample was subsequently measured at a faster heating rate. The a-PMMA prepared in microemulsions shows higher glass transition and higher structural relaxation than those of bulk sample of the same tacticity and the same molecular weight. When the annealing time is longer, additional enthalpy relaxation and glass transition were observed at higher temperatures due to partial self-aggregation of a-PMMA chains, which was proved by spectroscopic studies. (C) 2004 Published by Elsevier Ltd.