On the two-step phase transition behavior of the Poly(N-isopropylacrylamide) (PNIPAM) brush: different zones with different orders

Abstract

Poly(N-isopropylacrylamide) (PNIPAM) brushes integrating poly[oligo(ethylene glycol) methacrylate] (POEGMA) as the core were prepared via successive atom transfer radical polymerization (ATRP). The dynamic thermal phase transition behavior of PNIPAM brushes was studied by means of IR spectroscopy in combination with the perturbation correlation moving window (PCMW) technique and two-dimensional correlation spectroscopy (2Dcos) analysis. Compared with aqueous dispersions of PNIPAM brushes covalently bound to the surface of gold nanoparticles and hydrophobic hyperbranched polyester core, an increase in the double phase transition temperature was observed due to the existence of the POEGMA core, which was favourable to the hydrophilic condition. With PCMW analysis, the phase transition temperature (ca. 36 °C) as well as the transition temperature range (33–41 °C) during the heating process were determined. 2Dcos was employed to discern the sequence order of group motions during heating. It is concluded that the PNIPAM in the inner zone responds earlier than that located in the outer zone.