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

Abstract

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 mm 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.

Polymeric Nanoparticle Engineering: From Temperature-Responsive Polymer Mesoglobules to Gene Delivery Systems

“…Therefore, prolonged heating at (50−70°C ) temperatures of PIPOX aqueous solutions has been found to induce crystallization. 26,27 Scheme 4 clearly shows the mechanism of change in the conformation of the individual phases of the heating process. In general, the thermal response of aqueous PIPOX solutions is faster than that of PNIPAM solutions, both for aggregation and disintegration, which is most likely due to the relatively weaker hydrogen bonding capacity of PIPOX and the absence of partial vitrifying during mesoglobule formation.…”

Hybrid nanoparticles obtained from mixed mesoglobules

“…Apparently, such contents of PNIPAM are sufficient to restrict the dipole interactions between PIPOX macromolecules, which are considered to be responsible for the crystallization of PIPOX [17,19,36].…”

Bioinspired Poly(2-oxazoline)s

“…PiPrOx, however, may even crystallize in hot aqueous solution to yield a coagulate of uniform microspheres built of crystalline nanofibers (Figure 8) [11]. Crystalline nanofibers could always be observed, but the morphology on the micrometer length scale was found to depend strongly on the environmental conditions, like for instance temperature [102], presence of a co-solvent, surfactant or salt and polymer end group charges. The kinetics of the crystallization process and the time-dependent evolution of the morphology were examined using wide-angle X-ray scattering (WAXS) and cryogenic/conventional scanning electron microscopy (SEM).…”

“…Figure 9. Evolution of the morphology produced during the annealing of a 1 wt% aqueous solution of PiPrOx as visualized by (a) cryogenic scanning electron microscopy (t ≤ 4 h) and (b) conventional scanning electron microscopy (t ≥ 4 h); the onset of crystallization occurred at t ~ 4 h (WAXS) [102], reproduced by permission of the Royal Society of Chemistry.…”