The control of particle size and its distribution has become more and more important both in theory and in practice in emulsion polymerization field．In this study

emulsion polymerization of methyl methacrylate (MMA)

ethyl acrylate (EA) and acrylic acid (AA) was carried out in the absence of emulsifier

and the influences of ingredients and conditions on polymerization

latex particle size and its distribution were investigated

and latex particles with narrow size distribution as well as with carboxyl groups on their surface were synthesized．The results showed that the high monomer conversion and narrow latex particle size distribution were obtained when large amount of initiator (APS) was introduced into the polymerization system at the beginning in three-step addition process. With the increase of APS and AA

the particle size decreased and the monomer conversion increased

and a similar result was also observed with the temperature increase．It was found that NH4HCO3 is a key material for the control of particle diameter (Dp). Dp increased with the increase of amount of NH4HCO3

and the Dp of monodispersed P(MMA-EA-AA) latex particles can be well controlled in the range from 300 to 600 nm by adjusting the amount of NH4HCO3 used．Moreover

latexes with high monomer conversion and narrow particle size distribution can be obtained when a moderate stirring rate of 300 r／min was selected．