Abstract: The particle formation mechanism of MMA/BA emulsifier-free emulsion polymerization in the presence of small amount of ZA-6 comonomer(sodium polyethylene glycol 600 maleate) was investigated with Coulter LS230 laser particle size analyzer. After the primary particles of the early stage have vanished, new small particles were twice found periodically. It is believed to be formed by new nucleations by theoretical and data analyses and is called periodic nucleation phenomenon. It is suggested that the nucleation processes do not end really at the middle and later stages of the polymerization, and it is in the dynamic equilibrium of nucleation and aggregation.

Key words: Emulsifier-free emulsion polymerization, Particle formation mechanism, Periodic nucleation phenomenon