Study of the core-shell nanoparticle formed through the "coil-to-globule" transition of poly(N-isopropylacrylamide) grafted with poly(ethylene oxide)

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 (M-w = 7.29 x 10(6) and 7.85 x 10(5) g/mol) were prepared by free radical copolymerization of N-isopropylacrylamide and poly(ethylene oxide) macromonomers end-capped with methacrylate (M-w = similar to 7000-8000) in water. At room temperature, PNIPAM-g-PEO in water exists as individual chains. When the temperaturte is higher than similar to 32 degrees 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.