Controlled association of amphiphilic polymers in water: Thermosensitive nanoparticles formed by self-assembly of hydrophobically modified pullulans and poly(N-isopropylacrylamides)

Thermoresponsive hydrogel nanoparticles were prepared by self-assembly of t wo different hydrophobically modified polymers, namely a cholesterol-bearin g pullulan (CHP) and a copolymer of N-isopropylacrylamide (NIPAM) and N-[4- ( 1-pyrenyl)butyl]-N-n-octadecylacrylamide (PNIPAM-C18Py), The interactions between CHP and PNIPAM-C18Py were investigated by fluorescence spectroscop y, dynamic light scattering, and size exclusion chromatography. After ultra sonication of a mixture of CHP and PNIPAM-C18Py (5:1 by weight) at 25 degre es C, monodisperse nanoparticles (Dh = 45 nm) were obtained, consisting of self-assembly of the two polymers associated via their hydrophobic moieties . Evidence from fluorescence and dynamic light scattering demonstrated that , above 32 degrees C, the lower critical solution temperature (LCST) of PNI PAM-C18Py, the colloidal mixed nanoparticles increase in diameter (from 47 to 160 nm), but no macroscopic aggregation could be detected. This phenomen on was thermoreversible: upon cooling the particles recovered their origina l diameter.