Temperature-induced phase separation and hydration in poly(N-vinylcaprolactam) (PVCL)–D₂O solutions were investigated by a combination of NMR and ATR FTIR spectroscopy, SAXS and model quantum-chemical calculations. The existence and character of water bound in PVCL globular-like structures were shown by NMR spin–spin relaxation times of HDO molecules and by FTIR spectroscopy. From FTIR spectra combined with DFT calculations it follows that the amount of fully dehydrated carbonyl groups in PVCL globular structures is rather small. Dehydration at temperatures above the LCST transition mainly consists of transformation of structures where a PVCL carbonyl is directly hydrogen bonded to two water molecules to structures with a single hydrogen bonded water molecule and breaking away indirectly bound water. In the transition region the changes of hydrophilic and hydrophobic interactions proceed simultaneously. The strong dependence of transition temperatures on polymer concentration was revealed by NMR and SAXS. NMR spectroscopy also enabled us to determine thermodynamic parameters ΔH and ΔS characterizing the phase transition. SAXS results have shown that above the transition temperature “primary” mesoglobules of 50 nm in size are formed which aggregate into large agglomerates.

The formation of the hydrogel poly(N-isopropylacrylamide)–clay (LAPONITE®) by redox polymerization was investigated, and the main factors governing the gel build-up were determined. The significant effect of the redox initiating system ammonium peroxodisulfate (APS) and tetramethylethylenediamine (TEMED) on gel formation and structure was established, making it possible to control the structure of the gel. Moreover, the pre-reaction stage involving the quality of the clay exfoliation in an aqueous suspension and the interaction of reaction components with the clay play a role in controlling the polymerization and gel structure. The molecular and phase structure evolution during polymerization was followed in situ by the following independent techniques: Fourier transform infrared spectroscopy (FTIR), chemorheology, small-angle X-ray scattering (SAXS) and ultraviolet-visible spectroscopy (UV/Vis). The combination of these methods enabled us to describe in detail particular progress stages during the gel formation and determine the correlation of the corresponding processes on a time and conversion scale. The mechanism of gel formation was refined based on these experimental results.