Thermoresponsive nanospheres with a regulated diameter and well-defined corona layer.

In the present work, we prepared core-corona-type nanospheres bearing a thermoresponsive polymer with a controlled chain length on their surface. The corona layers were composed of poly(N-isopropylacrylamide) (PNIPAAm) chains (Mn = 3000-18,000) with a narrow polydispersity index prepared by atom-transfer radical polymerization (ATRP). Nanospheres were prepared by dispersion copolymerization of styrene with the PNIPAAm macromonomer in a polar solvent. The obtained nanospheres were monodisperse in diameter. The diameter of the nanospheres was regulated either by the number or chain length of the PNIPAAm macromonomers. In fact, the nanosphere diameter was regulated from ca. 100 to 1000 nm. When two types of PNIPAAm macromonomers are used, the obtained nanospheres have two different kinds of PNIPAAm on their surface. The surface of the nanospheres was observed to be thermoresponsive nanosphere in 0, 50, 100 mmol L(-1) NaCl aqueous solution. The nanosphere diameter and the surface-grafted polymer were concurrently adjusted for use in biomedical applications.