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Phase Separation in Poly( N,N ‐diethylacrylamide)/D 2 O Solutions and Physical Gels as Studied by 1 H NMR Spectroscopy
Author(s) -
Spěváček Jiří,
Hanyková Lenka,
Ilavský Michal
Publication year - 2001
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/1521-3935(20010401)202:7<1122::aid-macp1122>3.0.co;2-2
Subject(s) - lower critical solution temperature , thermotropic crystal , chemistry , phase transition , spectral line , nmr spectra database , analytical chemistry (journal) , phase (matter) , proton nmr , polymer , spectroscopy , thermodynamics , chromatography , stereochemistry , copolymer , organic chemistry , physics , quantum mechanics , liquid crystalline , astronomy
The structural‐dynamic changes during temperature‐induced phase separation in poly( N,N ‐diethylacrylamide) (PDEAAm)/D 2 O solutions and physical gels in a broad range of concentrations ( c = 0.5–50 wt.‐%) were studied by conventional high‐resolution and MAS 1 H NMR spectra. In the whole concentration range, irrespective of whether the studied system is a solution ( c < 5 wt.‐%) or physical gel ( c > 5 wt.‐%), the phase transition is manifested by line broadening (linewidth ≈ 3.6 kHz) of a major part of PDEAAm units, evidently due to the formation of compact globular‐like structures. 1 H MAS NMR spectra have shown that this broadening is not due to near‐static dipolar interactions. The respective motion is effectively isotropic with correlation time ≈ 1 μs, probably corresponding to Brownian tumbling of the whole globular particles. The thermotropic phase transition, as revealed by NMR, is not discontinuous, but ≈ 6 K broad (302–308 K). Above the LCST transition, the fraction p * of PDEAAm segments in globular‐like structures is between ≈ 0.94–1.0, independent of the polymer concentration. At temperatures below the LCST a certain preaggregation of PDEAAm is indicated by smaller line broadening (linewidths ≈ 100 Hz) in the 1 H NMR spectra.