Change in Solvation of Poly(N,N-diethylacrylamide) during Phase Transition in Aqueous Solutions As Observed by IR Spectroscopy

Abstract

Phase transitions of poly(N,N-dimethylacrylamide) (PdEA) in water and methanol/water mixture were investigated by Fourier transform infrared (FTIR) spectroscopy. IR spectra of the solutions measured as a function of temperature exhibited critical changes upon the phase transition. The amide I band of PdEA consists of three components centered at 1638, 1619, and 1599 cm -1 , which can be assigned to free carbonyl groups and those connected to one and two water molecules through hydrogen bonds, respectively. The relative areas of the 1619 and 1599 cm -1 components decrease and that of the 1638 cm -1 component increases above the phase transition temperature (Tp), but the change is relatively small and most of the amide CdO groups remain hydrated even above Tp. The C-H stretching bands shift toward lower wavenumbers that are close to those measured in the neat solid state, indicating that the alkyl groups are almost fully dehydrated above T p. In the methanol/water mixture, Tp is almost independent of methanol concentration up to ca. 20% and increases steeply above ca. 30%. The heat of transition (∆H) decreased linearly with an increase of methanol concentration up to 30% and is nearly zero above 40%. The areas of the 1599 and 1638 cm -1 bands decrease with an increase in methanol concentration with a slight change in the 1619 cm -1 band. The result suggests that methanol replaces parts of the CdO‚‚‚H-O-H hydrogen bonds to form a CdO‚‚‚H-O-CH3 hydrogen bond, and its bulky methyl group prevents the carbonyl group to form the second hydrogen bond that is responsible for the 1599 cm -1 band.

Study of the temperature-induced aggregation of polyoxometalate-poly(N,N-diethylacrylamide) hybrids in water

“…22,33 Above the TT most of the amide carbonyl groups are then hydrated with one water molecule, whereas the ethyl groups become fully dehydrated. 35 This only partial dehydration above TT allows to stabilize the aggregates at high temperature (named mesoglobules), avoiding their macroscopic precipitation.…”

Interplay between Hydrogen Bonding and Macromolecular Architecture Leading to Unusual Phase Behavior in Thermosensitive Microgels

“…The middle peak at 1625 cm À1 , which can be ascribed to C = O groups in a more hydrophobic (less hydrated) environment, shows a slight decrease at the phase transition only. [11,13] With increasing temperature, the intensity of the first peak (at 1597 cm À1 ) decreases strongly and the second peak (at 1625 cm À1 ) slightly, which indicates dehydration; that is, the local environment of the C=O groups becomes more hydrophobic in the collapsed state. In addition, the number and strength of intramolecular hydrogen bonds increase at the expense of intermolecular hydrogen bonds.…”

Fabrication and characterization of bifunctional spherical polyelectrolyte brushes

“…[26,27] Due to the presence of amide hydrogen acted as both H donor and accepter in NIPAM (not in DEA), the PNIPAM is more hydrophilic and more thermo-sensitive than PDEA. [28][29][30][31] AA monomer is a common material for polyelectrolyte chains and has been proved to be an effective way to adjust the LCST of thermo-sensitive polymers. [32][33][34] Two sets of SPBs (P(NIPAM-AA) and P(AA-DEA)) were made by photoemulsion polymerization.…”