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 (T p). Above T p 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 T p of PVCL, whereas KI and KBr raise T p. Addition of methanol gradually raises T p up to ca. 40 vol % and steeply raises T p at > 40 vol %. Although these salts do not alter the profiles of IR spectra of PVCL, methanol induces a change in the amide I band.

3‐Ethylated N‐Vinyl‐2‐pyrrolidone with LCST Properties in Water

“…Compared to poly(vinylcaprolactam) (PVCL) of the same molecular weight and concentration, the T c of 5 is about 7 8C lower, [2,[14][15][16] although the monomer units are isomers. The attached ethylene group shields the vicinal polaric carbonyl group partially from the water phase and causes a higher hydrophobicity of the polymer.…”

“…This behavior can be controlled partially by addition of surfactants, salts, or co-solvents. [1][2][3] Apart from this, it is possible under certain conditions to influence the T c by supramolecular interactions with cyclodextrins, [4][5] simply by copolymerization, or by chemical modification of the monomer unit. Among the widely used hydrophilic polymers, poly-(N-vinyl-2-pyrrolidone) (PVP) is a highly investigated, water-soluble, uncharged, and non-toxic macromolecule with various applications, [6,7] which include pharmaceutical use in drug-delivery systems.…”

“…However, in an aqueous 1.5 M KF, solution PVP shows an LCST behavior at 30 8C. [2] If N-vinyl-2-pyrrolidone (NVP) 1 is copolymerized with more hydrophobic comonomers, some usual LCST effects can be achieved. [12] However, because of the differences in the radical reactivity of NVP 1 and, e.g., acrylates, [13] only a few copolymers are described in the literature.…”

“…[2,[14][15][16] To mimic this effect, we were encouraged to modify the industrially used NVP 1 with one additional ethyl substituent to achieve the same elemental composition as NVCL 2 ( Figure 1). In the present paper, we describe the synthesis of the ethyl-modified 3-ethyl-1-vinyl-2-pyrrolidone (3) and the preparation of its homopolymer and copolymers.…”

Approaches to Chemical Synthesis of Protein-Like Copolymers

“…Such a length is too short to cause pronounced heatinduced phase separation effects typical for the thermoresponsive NVClcopolymers. However, the phase transition for such thermally precipitating fractions started at the temperatures 33-44 • C, i.e., in the region of T cp values characteristic of the NVCl-homopolymers (32-45 • C, depending on the polymer molecular weight [28,30,31,33,34]). Therefore, it can be assumed that all the NVCl/NVIAz-copolymers of the o-and p-types were not the random copolymers with the short oligoNVCl segments.…”