Molecular Evolution of Poly(2-isopropyl-2-oxazoline) Aqueous Solution during the Liquid–Liquid Phase Separation and Phase Transition Process

Abstract

A detailed phase transition process of poly(2-isopropyl-2-oxazoline) (PIPOZ) in aqueous solution was investigated by means of DSC, temperature-variable (1)H NMR, Raman, optical micrographs, and FT-IR spectroscopy measurements. Gradual phase separation accompanied by large dehydration degree and big conformational changes above the lower critical solution temperature (LCST) and facile reversibility were identified. Based on the two-dimensional correlation (2Dcos) and perturbation correlation moving window (PCMW) analyses, the sequence order of chemical group motions in phase transition process was elucidated. Additionally, a newly assigned CH3···O═C intermolecular hydrogen bond at 3008 cm(-1) in the PIPOZ system provides extra information on the interactions between C-H and C═O groups. The formation of cross-linking "bridging" hydrogen bonds C═O···D-O-D···O═C (1631 cm(-1)) is proposed as the key process to induce the liquid-liquid phase separation and polymer-rich phase formation of PIPOZ solution. With slow heating, more and more "bridging" hydrogen bonds were formed and D2O were expelled with an ordered and mostly all-trans conformation adopted in the PIPOZ chains. On the basis of these observations, a physical picture on the molecular evolution of PIPOZ solution during the phase transition process has been derived.

Probing carbonyl–water hydrogen-bond interactions in thin polyoxazoline brushes

“…Formation of the latter could be a result of interchain association and steric hindrance within the brush layer. 18 For PiPrOx in solution, the frequency of the bridging hydrogen bonds is supposed to be around 1630 cm À1 , 18,37 which is close to the observed 1628 cm À1 position for PcPrOx. Second-derivative spectra of the copolymer in D 2 O (Fig.…”

“…4, bottom) show that the deswelling behavior takes place gradually and is stretched over the entire measured temperature range. This is in contrast to the steplike phase transition of poly(2-oxazoline)s in solution, 24,37 and also to PNIPAAm, which shows a steplike transition around the LCST both in solution 6 and in the form of brushes. 7,31 For PcPrOx in D 2 O, two hydrated carbonylstretching components are measured at 1618-1628 cm À1 and 1600 cm À1 .…”

pH- and temperature-induced release of doxorubicin from multilayers of poly(2-isopropyl-2-oxazoline) and tannic acid

“…Importantly, Wu and co‐workers reported much smaller hysteresis in the reversible phase transition of PIPOX than of PNIPAM within a temperature range from 26 °C to 46 °C. They correlated this difference in the behaviour of PIPOX and PNIPAM with the presence of intermolecular hydrogen bonds in PNIPAM obstructing the dissociation of PNIPAM globules . Different from PNIPAM, PIPOX does not contain hydrogen donating groups.…”

Layer‐By‐Layer Modified Superparamagnetic Iron Oxide Nanoparticles with Stimuli‐Responsive Drug Release Properties

“…Poly(2‐alkyl‐2‐oxazoline)s exhibit important biological properties, for example, biocompatibility, nontoxicity, antifouling, and stealth behavior . Among poly(2‐alkyl‐2‐oxazoline)s, PIPOX is of interest for biomedical applications due to its LCST‐type phase behavior around 36 °C . TA is a natural polyphenol and also displays important biological properties such as antitumor, antioxidant, antibacterial, antienzymatic and antimutagenic activities .…”

“…[27][28][29][30][31][32] Among poly(2-alkyl-2-oxazoline)s, PIPOX is of interest for biomedical applications due to its LCSTtype phase behavior around 36 °C. [33] TA is a natural polyphenol and also displays important biological properties such as antitumor, antioxidant, antibacterial, antienzymatic and antimutagenic activities. [34] On the other hand, LbL technique may be considered advantageous over other synthetic coating methods for surface modification of SPIONS due to possibility of preparing multiple responsive coatings without need for chemical synthesis and purification steps.…”