Role of alkali-soluble random copolymer in emulsion polymerization

Alkali-soluble random copolymer (ASR), poly(styrene/alpha-methylstyrene/acrylic acid) was used as a polymeric emulsifier in the emulsion polymerization of styrene and methyl methacrylate, respectively. ASR could form aggregates like micelles and the solubilization ability of the aggregates was dependent on the neutralization degree of ASR. The rate of polymerization of styrene decreased as the neutralization degree of ASR was increased with little change in particle size. This result can be explained by the solubilization ability of ASR aggregate and the entry rate of radicals into the particle. As the degree of neutralization of ASR increased, the ASR aggregate was less efficient in solubilizing the monomer, and it was more difficult for radicals to enter the particle through the extended ASR layer on the particle surface, which led to a decrease in the rate of polymerization. The polystyrene (PS) latexes prepared using ASR showed the monodispersed particle size distribution. On the other hand, the particle size distribution of poly(methyl methacrylate) (PMMA) latexes became broader as the neutralization of ASR increased. This could be explained by the effects of the water solubility of the monomer and the neutralization degree of ASR on particle formation.