Thermosensitive Behavior of Poly(N-isopropylacrylamide) Grafted Polystyrene Nanoparticles

Abstract

We analyzed the thermosensitive behavior of monodisperse polystyrene (PSt) nanopatticles having different densities and chain lengths of grafted poly(N-isopropylacrylamide) (PNIPAAm) on their surfaces. The PSt nanoparticles were synthesized by free radical copolymerization of styrene monomer with PNIPAAm macromonomers in mixed ethanol/water solvents. The grafted PNIPAAm densities on the PSt nanoparticle surfaces can be controlled by varying polymerization conditions such as reaction temperature and initiator concentrations. The nanoparticle sizes and densities of grafted PNIPAAm on their surfaces significantly affected temperature-response, which was investigated by dynamic laser light scattering. The larger PSt nanoparticle sizes and higher grafted PNIPAAm densities showed a more significant decrease in hydrodynamic diameters when temperature of dispersed solutions was raised above lower critical solution temperature of the linear PNIPAAm. The molecular weight of grafted PNIPAAm on nanoparticle surfaces had no relationship with a visible decrease in hydrodynamic diameter.