Thermosensitive nanospheres of low-density core – An approach to hollow nanoparticles

A novel strategy for the preparation of hollow core–shell nano- and microparticle is reported. Nanoparticle cores were created from poly(N-isopropylacrylamide) (PNIPAM) by controlled heating above the LCST of this polymer in the presence of a small amount of sodium dodecyl sulfate. Shells were formed by radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) dimethacrylate (PEG-DMA) as cross-linking agent. The PNIPAM particles were acting as nucleating agents so that core–shell colloidal particles of PNIPAM covered with cross-linked PHEMA resulted. Subsequent release of a part of the PNIPAM chains from the interior of the particles was obtained by dialysis. The sizes and the temperature behavior of obtained particles were measured by DLS, TEM and SEM. The semi-hollow particles showed reversible volume response to cyclic temperature changes.