A Molecular Level Study of the Phase Transition Process of Hydrogen-bonding UCST Polymers
Wenhui Sun, and Peiyi Wu*. Molecular Level Study of the Phase Transition Process of Hydrogen-Bonding UCST Polymers. Phys. Chem. Chem. Phys. 2018, 20, 20849-20855.
Most of the existing topics focused on the development of lower critical solution temperature (LCST) behavior of thermoresponsive polymers, whereas the research on the upper critical solution temperature (UCST) behavior from a molecular view was extremely rare. In this work, molecular level study of the UCST thermal transition of poly N-acryloylglycinamide (PNAGA)-based in water and water/methanol mixture (6:1, v/v) was performed. Turbidimetry measurements exhibited the increased UCST and enlarged hysteresis of the thermal transition of the polymer with the addition of methanol. Fourier transform infrared (FTIR) spectral analysis indicated that the increased hydrophilicity among the C-H groups along the polymer chains upon heating induced UCST-type transition of the polymers in water, while the hydrogen bonding transformation predominated the thermal transition in the mixture. Moreover, in combination with two-dimensional correlation spectroscopy (2Dcos), the structures of different types of inter/intramolecular hydrogen bonds formed among the NAGA units have been distinguished and the transformation of the amide groups in PNAGA-based polymer from C=O•••D-N hydrogen bonds to C=O•••D2O ones during the UCST-type transition upon heating was captured