Hydroxyl end-functionalized poly(2-isopropyl oxazoline)s used as nano-sized colloidal templates for preparation of hollow polymeric nanocapsules

Hollow polymeric nanocapsules with a thermosensitive membrane are prepared and characterized. They reversibly change their dimensions during temperature variations below and above the transition of the membrane. The nanocapsules were prepared by three steps: (i) well-defined mesoglobules prepared from an LCST polymer (hydroxyl end functionalized poly(2-isopropyl-2-oxazoline), PiPOZ-OH) were coated with a thermo-sensitive cross-linked shell formed via seeded radical copolymerization of N-isopropylacrylamide (NIPAM) and N,N′-bis-methylene acrylamide to produce core-shell nanoparticles (ii), which were subjected to extensive dialysis below the LCSTs of both the core-forming PiPOZ-OH and shell-forming PNIPAM to remove the core (iii). The use of a core-forming polymer of low molecular weight (<8900 g mol−1), narrow dispersity (<1.15) and relatively low Tg (52-68 °C) is beneficial as far as the effectiveness of the removal of the cores is concerned. The inherent immiscibility between PiPOZ-OH and PNIPAM as well as the specific raspberry-like structure of the core-shell particles also contributed for enhancement of the core removal effectiveness.