Hydration and Phase Behavior of Poly(N-vinylcaprolactam) and Poly(N-vinylpyrrolidone) in Water

Abstract

Phase transitions of poly(N-vinylcaprolactam) (PVCL) and poly(N-vinylpyrrolidone) (PVPy) in H2O and D2O were investigated by turbidimetry, differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. The phase diagram of PVCL solution is binodal with a lower critical solution temperature (LCST) of 32.5 °C and a critical concentration of about 5 wt %. PVPy also undergoes a phase separation around 30 °C in aqueous 1.5 M KF solution. The IR spectra of PVCL and PVPy in water critically change at the phase transition temperature (Tp). Above Tp the C−H stretching and the C−H bending bands shift to lower wavenumbers. The amide I band of PVCL is divided into four components, and the intensities of the 1565, 1588, and 1625 cm-1 components increase and that of the 1610 cm-1 component decreases while the phase transition proceeds. Addition of KCl and KF lower Tp of PVCL, whereas KI and KBr raise Tp. Addition of methanol gradually raises Tp up to ca. 40 vol % and steeply raises Tp at >...