By using a three-step introduction of initiator at different time of polymerization

the emulsion copolymerization of methyl methacrylate(MMA)

ethyl acrylate(EA) and acrylic acid(AA) was carried out in the absence of emulsifier first at 80℃ for 7.5 h and then at 90℃ for 0.5 h．The distribution of —COOH in the latex was determined by conductometric titration

and effects of ingredients on the distribution of —COOH and the density of surface —COOH(Sd) were investigated. Results showed that N4HCO3 is a key material：with the increase of N4HCO3

the amount of surface —COOH(Sa)

water —COOH(Fa) and Sd increased

while the amount and percentage of embedded —COOH(Ea and Ep) decreased．Sa

Fa

Eaand Sd increased whereas Epdecreased with AA increase．It was found that Fa increased and then remain constant

and Sd deceased with the increase of initiator.