Synthesis of double-responsive magnetic latex particles via seeded emulsion polymerization using macroRAFT block copolymers as stabilizers

International audienceWe report an efficient method to synthesize stimuli-responsive magnetic latexes with high magnetic response. An amphiphilic poly(2-dimethylaminoethyl methacrylate)-b-polystyrene (PDMAEMA-b-PS) block copolymer was first synthesized by RAFT solution polymerization, and subsequently employed to stabilize iron oxide clusters. The resulting superparamagnetic clusters were then used as seeds in styrene emulsion polymerization generating magnetic latex particles with a strong response to a magnetic field, and decorated with double-responsive PDMAEMA segments. The incorporation of magnetic particles into polymer latexes has attracted increasing interest over the last 30 years owing to the wide potential of the resulting composite particles in removal of toxic contaminants, as magnetic support for cataly-sis, in targeted drug delivery, cancer diagnosis and therapy, and for magnetic separation or magnetic resonance imaging (MRI). 1 Such particles are commonly synthesized via (mini) emulsion polymerization of hydrophobic monomers in the presence of superparamagnetic iron oxide (IO) nanoparticles. 1,2 This approach nevertheless suffers from drawbacks, such as phase separation between the inorganic particles and the polymer, concomitant nucleation of polymer particles free of IO, and/or low IO content in the final magnetic particles, limitations that obviously negatively impact their performances. 3 Efficient strategies able to overcome these drawbacks have however been reported in the literature. 4-7 These rely on the preparation of IO clusters prior to their encapsulation by (mini)emulsion polymerization (i.e. clusters of IO nanoparticles are used, not the IO nanoparticles themselves). The successful formation of well-defined IO clusters indeed guarantees that a high amount of magnetic material is incorporated into the composite particles, endowing them with a fast magnetic response. In a typical clustering procedure, organically-modified IO nanoparticles are first dispersed in a non-polar solvent, such as toluene or octane. This organic phase is then dispersed in an aqueous surfactant solution using a high-energy emulsification device, forming sub-micron size droplets loaded with IO. In a last step, either the IO-loaded droplets themselves 6,7 or the IO clusters suspension obtained after solvent evaporation, 4,5 are used as seeds in emulsion polymerization resulting in the formation of hybrid particles with high IO contents (up to 80 wt%). 7 On the other hand, the development of nano-objects with controlled surface reactive groups is the focus of many studies due to the potential applications of such functional nano-particles, especially in the field of nanomedicine. 8 One successful strategy to design polymeric nanoparticles with well-defined surface functionalization relies on the use of reversible addition-fragmentation chain transfer (RAFT) polymeriz-ation. 9 The versatility of the RAFT technique over a wide range of functionalities together with the ability to access well-defined macromolecular architectures, notably in dispersed media, make it now possible to engineer a variety of functional particles. 10 Furthermore, when stimuli-responsive polymer chains are used to decorate the particle surface, the resulting materials can exhibit CO 2-, 11 thermo-and/or pH-responsive properties 12 allowing their use in biomedicine. 12 The combination of RAFT and (mini)emulsion polymerization to prepare magnetic latex particles has already been reported in the literature. 13-15 In particular, our group recently described the successful preparation of magnetic latex particles exhibiting fully encapsulated morphology and stabilized by poly(acrylic acid-con -butyl acrylate) segments using the RAFT-assisted encapsulating emulsion polymerization process. 14 However, to the best of our knowledge, the combined usage of RAFT polymerization and IO clusters formation is an appealing research direction that has never been investigated so far. In this work we report the synthesis of magnetic latex particles decorated with double-stimuli responsive PDMAEMA † Electronic supplementary information (ESI) available. Se