Abstract: Soap-free copolymerization of methyl methacrylate(MMA) and butyl acrylate(BA) in the presence of surface active comonomer, sodium undecylenate (at concentration below its CMC) was carried out.The particle size(D_w), number(N_p), morphology and surface properties were charaterized with particle size analysizer, TEM and ion-exchange-conductimetric titration respectively.The results indicated that D_w and N_p could be controlled by adjusting the temperature , the concentration of SUAand KPS, ionic strength, and the ratio of MMA to BA, while the particle surface properties were decided by SUA content, ionic strength and the ratio of MMA to BA.

Key words: Soapless emulsion copolymerization, Reactive emulsifier, Surface properties of particle