Abstract: The nucleation mechanism of polymer latex particles and formation processes of monodispersed latex particles in MMA/BAemulsifier free emulsion polymerization in the presence of small amount of water-soluble comonomer(such as sodium sulfonated polyethylene glycol allyl ether glycerin succinate) were investigated with Coulter LS230 laser particle size analyzer. The colloidally stable polymer latex particles were formed from multi step particle formation mechanism: the coagulation of colloidally unstable precursor particles subsequent to their formation by homogeneous nucleation, and growth due to both aggregation and propagation. The particle monodispersion was not formed in the early stage, but formed through a process of increasing and then decreasing in particle polydispersity, U= D_w/ D_n. This can be ascribed to the competition of homogeneous nucleation coagulation propagation-aggregation, and it also leads to the periodic-nucleation-phenomena in the early stage of polymerization.

Key words: Emulsifier-free latex, Monodispersed particles, Formation processes, Particle formation machanism