Study of the Core−Shell Nanoparticle Formed through the “Coil-to-Globule” Transition of Poly(<i>N</i>-isopropylacrylamide) Grafted with Poly(ethylene oxide)

Abstract

A combination of static and dynamic laser light scattering (LLS) was used to study the “coil-to-globule” transition of poly(N-isopropylacrylamide) grafted with poly(ethylene oxide) (PNIPAM-g-PEO) in water. Two PNIPAM-g-PEO samples (Mw = 7.29 × 106 and 7.85 × 105 g/mol) were prepared by free radical copolymerization of N-isopropylacrylamide and poly(ethylene oxide) macromonomers end-capped with methacrylate (Mw = ∼7000−8000) in water. At room temperature, PNIPAM-g-PEO in water exists as individual chains. When the temperaturte is higher than ∼32 °C, the PNIPAM-g-PEO chain backbone undergoes the intrachain “coil-to-globule” transition and the interchain aggregation to form nanoparticles with a hydrophobic PNIPAM core and a soluble hydrophilic PEO shell. The nanoparticle size decreases as the average number of PEO chains grafted on the PNIPAM chain backbone increases. A lower copolymer concentration and a fast heating rate can also lead to smaller nanoparticles. With a proper control of the formation conditions, we were able to suppress the interchain aggregation to prepare and study a single chain core−shell nanostructure.