Nucleation mechanism of MMA/BA semi-continuous emulsion copolymerization

In semi-continuous emulsion polymerization with methyl methacrylate (MMA) and butyl acrylate (BA) as the monomers, the influences of the ratio of MMA to MMA and the pH buffer (NaHCO3) on the nucleation process were investigated. The nucleation mechanism was deduced by analyzing the growth of particle size and its distribution during the polymerization process. Experiment results show that the nucleation mechanisms are determined by the molar fraction of MMA (FMMA), when fMMA increases the reaction time of nucleation t1,2 decreases, but the number of emulsion particles Npmax increases at the end of nucleation except BA homogenous polymerization; when fMMA=0.5763, as the amount of NaHCO3 increases the conversion rate of the monomers increases, but t1,2 remains constant, 16 min, which indicates the coexistence of the micellar nucleation and homogenous nucleation mechanisms. The coexistence of the two nucleation mechanisms can also be verified by the analysis of the particle size and distribution of the emulsions.