Polymerization of styrene with ionic comonomer, nonionic comonomer, or both

Nanosized polystyrene latexes with high polymer contents were obtained from an emulsifier-free process by the polymerization of styrene with ionic com onomer, nonionic comonomer, or both. After seeding particles were generated in an initial emulsion system consisting of styrene, water, an ionic comon omer [sodium styrenesulfonate (NaSS)] or nonionic comonomer [2-hydroxyethyl methacrylate (HEMA)], and potassium persulfate, most of the styrene monome r or a mixture of styrene and HEMA was added dropwise to the polymerizing e mulsion over 6 h. Stable latexes with high polystyrene contents (less than or equal to 25%) were obtained. The latex particle weight-average diameters were largely reduced (41 nm) by the continuous addition of monomer(s) comp ared with those (117 nm) obtained by the one-pot polymerization method. Lat ex particles varied from about 30 to 250 nm in diameters, whereas their mol ar masses were within 10(4) to 10(5) g/mol. The effect of the comonomer con centration on the number of polystyrene particles per milliliter of latex a nd the weight-average molar masses of the copolymers during the polymerizat ion are discussed. The surface compositions of the latex particles were ana lyzed by X-ray photoelectron spectroscopy, which indicated that the surface of the latex particles was significantly enriched in NaSS, HEMA, or both. (C) 2001 John Wiley & Sons, Inc.