Surface Functionalization of Magnetic Nanoparticles Using a Thiol-Based Grafting-Through Approach

Here we describe a simple and straightforward synthesis of different multifunctional magnetic nanoparticles by using surface bound thiol-groups as transfer agents in a free radical polymerization process. The modification includes a first step of surface silanization with (3-mercaptopropyl)trimethoxysilane to obtain thiol-modified nanoparticles, which are further used as a platform for modification with a broad variety of polymers. The silanization was optimized in terms of shell thickness and particle size distribution, and the obtained materials were investigated by dynamic light scattering (DLS), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). Subsequently, the free radical polymerization of different monomers (tert-butyl acrylate (tBA), methyl methacrylate (MMA), styrene, 2-vinyl pyridine (2VP), and N-isopropylacrylamide (NIPAAm)) was examined in the presence of the thiol-modified nanoparticles. During the process, a covalently anchored polymeric shell was formed and the resulting core–shell hybrid materials were analyzed in terms of size (DLS, TEM), shell thickness (TGA, TEM), and the presence of functional groups (attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FT-IR)). Hereby, the shell leads to a different solution behavior of the particles and in some cases an increased stability towards acids. Moreover, we examined the influence of the nanoparticle concentration during polymerization and we found a significant influence on dispersity of the resulting polymers. Finally, we compared the characteristics of the surface bound polymer and polymer formed in solution for the case of polystyrene. The herein presented approach provides straightforward access to a wide range of core–shell nanocomposites.