Summary: Compartmentalization in atom transfer radical polymerization (ATRP) in dispersed systems at low conversion (<10%) has been investigated by means of a modified Smith–Ewart equation focusing on the system n‐butyl acrylate/CuBr/4,4′‐dinonyl‐2,2′‐dipyridyl at 110 °C. Compartmentalization of both propagating radicals and deactivator was accounted for in the simulations. As the particle diameter (d) decreases below 70 nm, the polymerization rate (Rp) at 10% conversion increases relative to the corresponding bulk system, goes through a maximum at 60 nm, and thereafter decreases dramatically as d decreases further. This behavior is caused by the separate effects of compartmentalization (segregation and confined space effects) on bimolecular termination and deactivation. The very low Rp for small particles (d < 30 nm) is due to the pseudo first‐order deactivation rate coefficient being proportional to d−3.Simulated propagating radical concentration ([P•]) as a function of particle diameter (d) at 10% conversion for ATRP of n‐butyl acrylate ([nBA]0 = 7.1 M, [PBr]0 = [CuBr/dNbpy]0 = 35.5 mM) in a dispersed system at 110 °C. The dotted line indicates the simulated [P•] in bulk at 10% conversion.magnified imageSimulated propagating radical concentration ([P•]) as a function of particle diameter (d) at 10% conversion for ATRP of n‐butyl acrylate ([nBA]0 = 7.1 M, [PBr]0 = [CuBr/dNbpy]0 = 35.5 mM) in a dispersed system at 110 °C. The dotted line indicates the simulated [P•] in bulk at 10% conversion.

Micrometer-sized silica-stabilized polystyrene latex particles and submicrometer-sized polystyrene−silica nanocomposite particles have been prepared by dispersion polymerization of styrene in alcoholic media in the presence of a commercial 13 or 22 nm alcoholic silica sol as the sole stabilizing agent. Micrometer-sized near-monodisperse silica-stabilized polystyrene latexes are obtained when the polymerization is initiated with a nonionic AIBN initiator. These particles are stabilized by silica particles that are present on the latex surface at submonolayer concentration. The total silica content is no greater than 1.1 wt %, which corresponds to a silica sol incorporation efficiency of less than 1.3%. Reduction of the initial silica sol concentration led to a systematic increase in the mean latex diameter. In contrast, submicrometer-sized polystyrene-silica nanocomposite particles are obtained when the polymerization is initiated with a cationic azo initiator. The silica contents of these nanocomposite particles are significantly higher, ranging up to 29 wt %. Zeta potential measurements, XPS, and electron spectroscopy imaging by transmission electron microscopy (ESI/TEM) studies reveal a well-defined core−shell morphology for these particles, whereby the core is polystyrene and the shell comprises the silica sol. After calcination, these nanocomposite particles can form hollow silica capsules. Variation of the initial silica sol and initiator concentration has relatively little effect on the final particle size and silica content of these polystyrene−silica nanocomposite particles, but indicates silica sol incorporation efficiencies up to 72%.

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"Mushroom-like" Janus poly(methyl methacrylate) (PMMA)/poly(styrene-2-(2-bromoisobutyryloxy)ethyl methacrylate)-graft-poly(2-(dimethylamino)ethyl methacrylate) (PDM) particles synthesized in our previous report were applied as particulate surfactants. The PDM moiety at the one side of the Janus particles reversibly exhibited the volume phase transition in response to pH and temperature in an aqueous medium; that is, the surface property of the Janus particles comprising both PDM and PMMA reversibly changed between amphiphilic and hydrophobic based on the nature of PDM. Consequently, 1-octanol-in-water emulsion droplets stabilized by the amphiphilic Janus particles coalesced in the alkaline region and at 60 degrees C around neutral pH because of desorption of the hydrophobized Janus particles from the interface to the oil phase.

Nitroxide-mediated controlled/living dispersion polymerization of styrene in supercritical carbon dioxide (scCO2) has been performed successfully to high conversion using N-tert-N-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)] nitroxide (SG1) and a poly(dimethylsiloxane-b-methyl methacrylate) stabilizer at 110 °C. The molecular weight distributions were narrow (M w/M n = 1.12−1.43), and the number-average molecular weight (M n) values agreed well with theory. A large excess of free SG1 was required to obtain satisfactory control in the dispersion polymerization, possibly due to SG1 partitioning. The critical degree of polymerization at which the polymer precipitates (J crit) was determined as 28 by visual observation using a novel approach. Polymerizations conducted in solution (toluene) proceeded at a similar rate (∼20% faster) to those in scCO2. The number of chains increased with conversion in both dispersion and solution, with the greater increase being observed in the dispersion system.