The emulsion polymerization of styrene in the presence of hydrophilic poly(methacrylic acid-co-poly(ethylene oxide) methyl ether methacrylate), P(MAA-co-PEOMA), macromolecular RAFT (reversible addition−fragmentation chain transfer) agents possessing a trithiocarbonate reactive group and 19 ethylene oxide subunits in the grafts was performed to create in situ P(MAA-co-PEOMA)-b-polystyrene amphiphilic block copolymer self-assemblies. The system was studied using the following conditions: a pH of 5, two different compositions of the MAA/PEOMA units (50/50 and 67/33, mol/mol), different molar masses of the macroRAFT agents, and various concentrations of the latter targeting different molar masses for the polystyrene block. This work completes a previous one performed at pH 3.5, under otherwise similar experimental conditions, for which only spherical particles were obtained [Zhang et al. Macromolecules 2011, 44, 7584]. For both MAA/PEOMA compositions, the system led to different nano-object morphologies such as spherical micelles, nanofibers, and vesicles, depending directly on the molar masses of the hydrophilic and hydrophobic blocks. A pH of 5 was shown to be the best compromise to achieve nonspherical particles while keeping a good control over the chain growth.

The RAFT-mediated emulsion polymerization of styrene was carried out in a one-pot, two-step procedure using two poly-(methacrylic acid-co-poly(ethylene oxide) methyl ether methacrylate) macroRAFT agents of different compositions carrying a reactive trithiocarbonate end-group. The latter were prepared in situ, directly in aqueous solution at acid pH. In all cases, the synthesis was fast and efficient, leading to very high conversions and very good control over the polymer features. It was moreover particularly reproducible, which is an important outcome for the robustness of the method. Then, styrene was added and directly polymerized in the formed emulsion system until very high conversion in short reaction time. The method led to amphiphilic block copolymers, self-assembled into stable spherical particles. The diameter of the latter was directly governed by the initial concentration of macroRAFT agent, which also controlled the molar mass of the polystyrene block at constant styrene initial concentration. The emulsion polymerization step was studied in detail to provide information on the overall mechanism: nucleation, conversion rate, and chain growth. Because of the reduction of the number of synthesis and purification steps and of the overall reaction time, and due to the use of water as the sole reaction medium, the proposed method is of high interest in terms of both respect of environmental constraints and energy saving. ' INTRODUCTIONThe development of controlled/living free radical polymerization (CRP) 1À5 in aqueous emulsion systems has attracted much interest in the past 10 years due to the multiple advantages of the process (among others, it is environmentally friendly and favors high rates along with low viscosity) and the large number of industrial applications of the products. 6 Moreover, new possibilities are offered by the combination of both approaches. 7À14 For instance, the generation of amphiphilic block copolymers in situ, by taking advantage of the reactivity of water-soluble polymers tailored by CRP, leads to a new way of performing surfactant-free emulsion polymerization. The method leads to self-stabilized particles and can allow high solids content to be achieved, even under batch conditions. This strategy has been employed using the various CRP techniques available (mainly nitroxide-mediated radical polymerization, 15À20 organotellurium-mediated radical polymerization, 21,22 and RAFT for reversible additionÀfragmentation chain transfer 23À36 ). Most