FT-IR and 2D-IR spectroscopic studies on the effect of ions on the phase separation behavior of PVME aqueous solution

Thermosensitive phase transition behavior of poly(vinyl methyl ether) (PVME) in an aqueous solution and the effect of inorganic ions on the coil-globule transition have been investigated by Fourier transform infrared (FT-IR) spectroscopy with attenuated total reflection (ATR) accessory. ATR-IR spectra of PVME aqueous solution indicate that in water-PVME-inorganic salts system, the phase separation temperature of PVME aqueous solution decreased with the increase of ion concentration and the increase of anion electronegativity. Meanwhile, two-dimensional infrared (2D-IR) measurements have been made to clarify the microcosmic conformational changes of PVME during the coil-globule transition. Results show that the conformation changes of main chains occur earlier than those of ether groups during heating. Furthermore, the 2D correlation spectroscopy of PVME aqueous solution during heating and the increase of concentration of potassium chloride have been studied. The features of 2D-IR spectra during heating did not change compared to the features of PVME aqueous solution during the increase of concentration of potassium chloride. This result implies that, although the addition of inorganic ions shifts the phase separation temperature, it does not alter the internal mechanism of the coil-globule transition of PVME.