Mechanistic study of the phase separation/crystallization process of poly(2-isopropyl-2-oxazoline) in hot water

The kinetics of the crystallization of thermoresponsive poly(2-isopropyl-2-oxazoline) in water and the time-dependent evolution of the morphology were examined using wide-angle X-ray scattering and conventional and cryogenic scanning electron microscopy. Results indicate that a temperature-induced phase separation produces a bicontinuous polymer network-like structure, which with the onset of crystallization collapses into individual particles (1-2 mu m in diameter) composed of a porous fiber mesh. Nanofibers then preferentially form at the particle surface, thus wrapping the microspheres like a ball of wool. The particle morphology is severely affected by changes in temperature and less by the initial polymer concentration.