Crown Ether-Assisted Synthesis of Polystyrene Nanoparticles: Implications for Biomedicine and Electronics

Monodisperse polystyrene (PS) nanoparticles with widely tunable sizes (30–930 nm) were prepared by soap-free emulsion polymerization with the assistance of crown ethers. The effects of crown ether species and concentrations, initiator species, and monomer contents on the sizes of PS nanoparticles were investigated in detail. The presence of 18-crown-6 and 15-crown-5 in the reaction system will facilitate the polymerization rate of styrene and produce larger PS nanoparticles in comparison with the control group (without crown ethers), whereas the system with 12-crown-4 retards the polymerization rate significantly and brings the smallest PS nanoparticles. As the interface of monomer/water is the main locus of initial reaction for the thermally initiated emulsion polymerization, the crown ether/alkali complexes accumulated around the styrene/water phase play both catalyst and molecular fence roles in the styrene soap-free emulsion polymerization. The former promotes and the latter inhibits the growth of PS nanoparticles. The relative contribution of these functions ultimately determines the final particle size. The results indicate that particle nucleation in styrene soap-free emulsion polymerization in the presence/absence of crown ethers occurs via an aggregative nucleation mechanism. This study provides a facile method to synthesize nanoparticles with widely tunable sizes via soap-free emulsion polymerization with the help of crown ethers, which has great potentials in biomedical and electronic fields.