Preparation of polymeric core-shell and multilayer nanoparticles: Surface-initiated polymerization using in situ synthesized photoiniferters

We report here the development of a very flexible synthetic approach to generate core-shell nanoparticles below 100 nm diameter, whereby thin polymer shells are synthesized under nonaqueous conditions in a variety of organic solvents with diverse properties. This facilitates incorporation of a wide range of functional monomers and cross-linkers in the shell, without the need to make major changes to conditions or methodology. Polymer cores carrying benzyl chloride functionalities were prepared by conventional emulsion polymerization and then derivatized with sodium diethyldithiocarbamate to generate surface bound iniferters. Photoinduced second-stage surface-initiated polymerization (SIP) led to shell formation (measured as an increase in particle size by dynamic light scattering) with good control over the size distribution. The core-shell morphology of the particles generated was confirmed by transmission electron microscope (TEM) imaging and the composition of the shell layer with IR spectroscopy. The presence of ionic functionalities in the shell layer was verified by aqueous zeta potential titration studies. By exploiting the surface-initiated living radical mechanism, we have also synthesized complex multilayer particles sequentially. Even after the formation of an additional layer, the majority of the iniferter groups were re-formed as determined by elemental analysis; therefore, further particle elaboration would be possible if required