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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.

The cryopolymerization and formation of a macroporous poly(N-isopropylacrylamide) (PNIPA)/clay cryogel were investigated. The mechanism of the cryopolymerization and cryogel formation was elucidated. Two processes, cryostructuration and cryopolymerization, proceed simultaneously and their relative rates determine the structure evolution and the cryogel morphology – porosity. The cryostructuration in the PNIPA/clay system during freezing, controlled by the freezing temperature and the rate of cooling, includes both water and NIPA crystallization, formation of a highly concentrated non-frozen liquid phase (NFLP) and clay aggregation. The rate of cryopolymerization and gelation is governed by the following effects: by a low polymerization temperature and after freezing, by the high cryoconcentration and a steric confinement, manifested by a reduced reagent mobility. Moreover, it depends on the cooling rate and the evolution of cryostructuration. The progress of cryostructuration and cryopolymerization during freezing was described and experimentally proved step by step. Both the phase development during freezing and the progress of cryopolymerization including gelation were monitored in situ by NMR, DSC, chemorheology and SAXS. The morphology and porosity of the cryogels were characterized by SEM and TEM.

Thermoresponsive polymeric surfactant CAE85 is a telechelic carboxyl group derivative of Pluronic P85 and its carboxyl end-groups undergo deprotonation into carboxylate groups upon micellization. Micelle formation and disintegration were studied here by means of small angle X-ray scattering, FTIR and Raman spectroscopy, quantum mechanical calculations and dynamical mechanical analysis. The deprotonation was observed in aqueous solutions of CAE85 for concentrations from 5 wt% to 30 wt% at temperatures above the corresponding critical micellization temperature (CMT). The most likely cause is a difference between the proton dissociation constant of the micelle (pK(m)) and the proton dissociation constant of the unimers in solution (pK(a)); our observations indicate that pKmpK(a). For concentrations up to 15 wt%, the presence of carboxylate groups in CAE85 lowered the CMT in comparison with P85. In addition, the behavior of CAE85 was generally not thermo-reversible and reproducible upon cooling. Quantum chemical calculations showed that, in the dense micelle corona, the deprotonated states were more stable than hydrogen-bonded states of neutral molecules, which is likely to affect the equilibrium processes in the micelle. In contrast to the unmodified P85, no gelation was observed in the case of CAE85. By studying the processes at all the levels of organization from nanoscale charge formation through micellization to the macroscale process of gelation, our understanding of polymeric micelle formation may be advanced.

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.