Preparation of small-sized carboxylated latexes by emulsion polymerization using alkali-soluble random copolymer

Alkali-soluble random copolymer (ASR), poly(styrene/alpha-methylstyrene/acrylic acid) [M-n: 4,300; acid number: 190], was used as a polymeric emulsifier in the emulsion polymerization of styrene and methyl methacrylate, respectively. ASR containing a large number of carboxyl groups could form aggregates like micelles, and the solubilization ability of the aggregates was dependent on the neutralization degree of ASR. The polystyrene latexes prepared using ASR showed the small particle size (ca. 40 nm) and monodispersed particle size distribution, On the other hand, the particle size distribution of poly( methyl methacrylate) latexes became broader as the neutralization of ASR increased. This could be explained, by the effects of water solubility of the monomer and the neutralization degree of ASR on particle formation. Thin layer chromatography/flame ionization detector analysis confirmed that the grating reaction of polystyrene to ASR occurred during emulsion polymerization. The zeta potentials of final latexes showed high values due to ASR that was adsorbed and grafted on the surface of the latex particle. (C) 1998 John Wiley & Sons, Inc.