The semicontinuous polymerization of methyl methacrylate (MMA) in heterogeneous medium under monomer‐starved conditions is reported here. The effect of monomer addition rate on kinetics, particle size, particle number, and PMMA average molar masses are reported. This process permits the synthesis of high‐solid content latexes containing nano‐sized particles (<40 nm) with narrow particle size distributions [(Dw/Dn) < 1.1]. Moreover, the molar masses (Mn ≈ 0.3–1.2 × 106 g/mol) are much lower than those expected by chain transfer to monomer, which is the typical termination mechanism in 0–1 emulsion and microemulsion reactions. Both particle size and average molar masses decrease as the rate of monomer addition is diminished. Possible explanations for this process are provided. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1463–1473, 2007

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Silver nanoparticles precipitation was carried out at70∘Cin bicontinuous microemulsions stabilized with a mixture of surfactants sodium bis (2-ethylhexyl) sulfosuccinate/sodium dodecyl sulfate (2/1, w/w) containing an aqueous solution of 0.5 M silver nitrate and toluene as organic phase. Various concentrations of aqueous solution of sodium borohydride (precipitating agent) and their dosing times on microemulsions were studied. Regardless of dosing time, higher and medium concentrations of precipitating agent promoted the formation of worm-like nanostructures, while the lowest concentration allowed to obtain a mixture of isolated silver nanoparticles (mean diameter≈3 nm) and worm-like nanostructures. Experimental yields much higher than those typical in precipitation of silver nanoparticles in reverse microemulsions were obtained. An explanation for formation of worm-like nanostructures based on the development of local zones inside the microemulsions channels with high particle concentrations was proposed.

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Silver nanoparticles were precipitated at 70°C in a reverse microemulsion containing a high concentration of 0.5 M silver nitrate aqueous solution, toluene as organic phase, and a mixture of surfactants sodium bis (2-ethylhexyl) sulfosuccinate/sodium dodecyl sulfate (2/1, w/w). Nanoparticles were characterized by X-ray diffraction, atomic absorption spectroscopy, and high-resolution transmission electron microscopy. In spite of the high-water/surfactant molar ratio and concentration of silver nitrate solution used in this study, characterizations demonstrated that nanoparticles were silver crystals (purity >99%) with 8.6–8.8 nm in average diameter and 2.9–4.7 nm in standard deviation. It is proposed that slow dosing rate of aqueous solution of precipitating agent and the small molecular volume of toluene attenuated both particle aggregation and polydispersity widening. Experimental yield of silver nanoparticles obtained in this study was much higher than theoretical yields calculated from available data in the literature on preparation of silver nanoparticles in reverse microemulsions.

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The polymerization of vinyl acetate (VA) in three-component microemulsions stabilized with the cationic surfactant, cetyltrimethylammonium bromide (CTAB), is investigated as a function of concentrations of monomer and initiator (V-50) and temperature. Stable latexes containing small particles (35−50 nm) of poly(vinyl acetate) with average number molar masses of (4−5) × 105 g/mol are obtained. Analysis of the molar mass distributions (MMD) indicates that the controlling chain growth termination mechanism is chain transfer to monomer, and not to polymer, which is the dominant termination mechanism for the emulsion polymerization of this monomer, especially at high conversions. Deconvolution of the MMD curves and measurement of the radius of gyration as a function of molar mass show that more than 80% of the final polymer is linear, produced by chain transfer to monomer, whereas the rest may be branched, probably formed by chain transfer to polymer or by terminal double bond reactions. The population of linear polymer decreases with decreasing reaction temperature, but it is independent of initiator and monomer concentrations.