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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.

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A versatile approach for the preparation of micrometer-sized, monodisperse, "mushroom-like" Janus polymer particles in aqueous dispersed systems is proposed. The synthetic methodology of the Janus particles consists of the following two steps. The first step is the preparation of spherical poly(methyl methacrylate) (PMMA)/poly(styrene-2-(2-bromoisobutyryloxy)ethyl methacrylate) (P(S-BIEM)) Janus particles based on the internal phase separation induced by solvent evaporation from the solvent droplets dissolving the polymers. The second step is surface-initiated atom transfer radical polymerization (ATRP) of 2-(dimethylamino)ethyl methacrylate (DM) using the Janus particles with ATRP initiator groups at one side of the surface as macroinitiator. As a consequence, mushroom-like PMMA/P(S-BIEM)-graft-poly(DM) Janus particles were prepared, which had pH-responsive property.

The effects of partitioning of Cu(I) and Cu(II) species to the aqueous medium on the polymerization rate (R p), molecular weight and molecular weight distribution in the miniemulsion atom transfer radical polymerization system of styrene/CuBr/4,4‘-dinonyl-2,2‘-bipyridyl at 90 °C were investigated. According to both simulation (invoking the partitioning data for n-butyl methacrylate (Macromolecules 2000, 33, 7310−7320)) and experiment showed that the R p and polydipersity (M w/M n) were higher in miniemulsion than in the corresponding solution polymerization as a result of a decrease in deactivator concentration (Cu(II) species) in the organic phase. Simulations indicated quantitatively that the increase in M w/M n was caused by (i) a decrease of activation−deactivation cycles and (ii) an increase of bimolecular termination.