title: 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.
authors.affiliation: State Key Laboratory of Molecular Engineering of Polymers, Collaborative Innovation Center of Polymers and Polymer Composite Materials, Department of Macromolecular Science and laboratory for Advanced Materials, Fudan University, Shanghai 200433, China.
authors.forename: Tianjiao
authors.initials: T
authors.lastname: Li
authors.affiliation: State Key Laboratory of Molecular Engineering of Polymers, Collaborative Innovation Center of Polymers and Polymer Composite Materials, Department of Macromolecular Science and laboratory for Advanced Materials, Fudan University, Shanghai 200433, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Tang
authors.affiliation: State Key Laboratory of Molecular Engineering of Polymers, Collaborative Innovation Center of Polymers and Polymer Composite Materials, Department of Macromolecular Science and laboratory for Advanced Materials, Fudan University, Shanghai 200433, China.
authors.forename: Peiyi
authors.initials: P
authors.lastname: Wu
mesh_terms: D015394:Molecular Structure; D010080:Oxazoles / Q000737:chemistry*; D044367:Phase Transition; D066244:Proton Magnetic Resonance Spectroscopy; D012996:Solutions; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D010080:Oxazoles; D012996:Solutions; C000605739:poly(2-isopropyl-2-oxazoline); D014867:Water