Langmuir 1999, 15, 8067-8071
8067
Microemulsion Polymerization of Styrene for Obtaining High Ratios of Polystyrene/Surfactant X. J. Xu,† C. H. Chew,† K. S. Siow,† M. K. Wong,† and L. M. Gan*,†,‡ Department of Chemistry, National University of Singapore, and Institute of Materials Research and Engineering, Singapore 119260 Received April 12, 1999. In Final Form: June 30, 1999 A modified ternary microemulsion polymerization was successfully used to prepare nanosized polystyrene (PS) microlatexes with high PS/surfactant weight ratios of up to 14:1. Cationic surfactants used were alkyltrimethylammonium bromides, CnTAB, where n is either 12, 14, or 16. A water-soluble initiator was used for the polymerization at room temperature, with moderate stirring. The latexes obtained are bluishopaque and have been stable now for about 8 months. The process produced rather uniform (Dw/Dn = 1.10) latex particles of about 40 nm having high molar masses of PS ranging from 1.0 to 2.2 × 106 g/mol. This was obtained by first generating monomer-starved latex particles in a ternary microemulsion containing only 0.5-1.0 wt % styrene and 1.0 wt % cationic surfactant. The subsequent supply of styrene monomer to the polymerized microemulsion was delivered either through dropwise addition or via hollow-fiber feeding of monomer. The latter method was employed for the first time.
Introduction Microemulsion polymerization1-5 has been quite actively studied since 1980. The enormous number (∼1015 mL-1) of either water-in-oil or oil-in-water microemulsion droplets, which are transparent, is responsible for the fast polymerization of monomers and the formation of microlatex particles of less than 50 nm. Although, polystyrene and poly(methyl methacrylate) form small particles, molar masses exceeding one million can easily be obtained from microemulsion polymerization of styrene and methyl methacrylate. However, drawbacks of microemulsion polymerization include the required use of a low monomer/ surfactant weight ratio (1 < ω) and the production of only a relatively low polymer content (
