Synthesis of Magnetic Polystyrene Nanoparticles Using Amphiphilic Ionic Liquid Stabilized RAFT Mediated Miniemulsion Polymerization

Abstract

Imidazole based amphiphilic ionic liquids (ILs) were used as surfactants in miniemulsion polymerization (MEP) of styrene using a free radical process as well as reversible addition−fragmentation chain transfer (RAFT). Monodisperse polystyrene (PS) nanoparticles were obtained, demonstrating the efficiency of the amphiphilic IL as surfactant in MEP. IL stabilized miniemulsion was furthermore used to prepare polystyrene based magnetic nanoparticles (MNP). A large increase of the possible MNP content associated with very good colloidal stability was achieved using IL stabilized RAFT mediated MEP where a carboxyl functionalized chain transfer agent (CTA) was applied, allowing interaction with the MNP surface. The molecular weight and dispersity index of polystyrene, the content of MNP, and the morphologies of the hybrid nanoparticles were controlled by proper optimization of the concentration of initiator and CTA. The materials have been analyzed by NMR, GPC, DLS, SEM, TEM, and TGA. Finally, the magnetic properties of the materials were determined by vibrating sample magnetometer (VSM) analysis. ■ INTRODUCTIONPolymer magnetic composite (PMC) nanoparticles have raised a great deal of interest due to their potential use in several biomedical applications like magnetic resonance imaging, 1 nucleic acid purification, 2 enzyme immobilization, 3 drug delivery, 4 etc. The magnetic nanomaterials in the colloidal range have been successfully utilized in both therapeutic 5 and diagnostic 6 applications. The major challenge so far was the selection of suitable materials based on their various properties like particle size distribution, colloidal stability, content of MNP, presence of functionality, and most importantly toxicity. In the recent years, focus has also been turned on the synthesis of asymmetric polymer superparamagnetic composites for use as potential materials for applications in multimodal probes and biosensors. 7,8 Besides the biomedical applications, there are several demands for PMC nanoparticles in the production of toner materials 9 and also for the support and easy separation of catalyst in chemical reactions. 10 The above facts necessitate a fruitful technique to produce PMC nanoparticles in dispersion or as solid materials. Several methods have been developed which include microfluidic-based synthesis, 11 selective surface modification, 12 and different kinds of heterogeneous polymerization. 13,14 Among all these methods, miniemulsion polymerization (MEP) has been proven to be one of the most effective methods to prepare such materials. Regarding the synthesis of PMC nanoparticles using MEP, most of the work in the literature has proposed a single-step MEP process although no more than 20 wt % of MNP with respect to the polymer could be encapsulated. Landfester et al. 15 reported a strategy of multistep miniemulsion to encapsulate up to 40% MNP within the PS particles. Irrespective of the number of steps used for a successful encapsulation using MEP, several other parameters like nature of initiator, concen...

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