Water Properties in the Super-Salt-Resistive Gel Probed by NMR and DSC

Abstract

The so-called "super-salt-resistive gel", or poly(4-vinylphenol) (P4VPh) hydrogel, of different water contents ( H = 97-51%) was prepared by cross-linking with different amounts of ethylene glycol diglycidyl ether. 1H NMR spectroscopy was used to investigate the dynamic properties of water in the gel samples in terms of the spin-spin relaxation. The T2 values in those hydrogels were analyzed by assuming a two-component system, namely, T 2(long) and T2(short), and their fractions were obtained. In the higher water content region (75% < or = H < or = 97%), T2(long) for P4VPh gel was almost constant or even slightly increased with decreasing temperature. On the other hand, T2(long) for poly(vinyl alcohol) (PVA) gel (80% < or = H < or = 96%) significantly decreased with decreasing temperature, showing a natural behavior for water mobility in common hydrogels. Water in P4VPh gels of lower water contents ( H = 70% and 51%) also showed intriguing behaviors: the T2 values are much larger than those of gels with higher water contents and decreased with decreasing temperature only in the lower temperature range (<10 degrees C). The fraction of T2(long) values of P4VPh gel showed another contrast to those of PVA gel; the latter decreased with decreasing water content (normal behavior), while in the former gel the highest fraction (ca. 60% at 20 degrees C) was observed for a sample with the lowest water content ( H = 51%). On the other hand, the results of DSC measurements for P4VPh gel were less specific than those of T2 and comparable to those of common hydrogels such as PVA; with decreasing water content, the total amounts of free water and freezable bound water per polymer mass (g/g) decreased, while the amount of nonfreezing water per polymer also decreased.

Evaluation of water properties in HEA–HEMA hydrogels swollen in aqueous-PEG solutions using thermoanalytical techniques

“…Several methods were previously applied to determine the different types of water in hydrogels including NMR [14,15,16], dilatometry, conductivity measurements and thermal analysis [10,17,18 Different properties of hydrogels (such as oxygen permeability, the rate of drug release and release mechanism, etc.) can be adjusted by changing the water content in hydrogels.…”

Reentrant swelling behavior of poly(4-vinyl phenol) gel in aqueous organic solvent mixtures

“…The problem here is to identify which solvation and polymer-polymer interaction are mainly responsible for a swelling and a deswelling. Some hints are available from our previous findings; NMR and IR studies strongly suggested that hydration of P4VPh in hydrogel phase is specifically stabilized only when the acidic proton of the phenol OH is least consumed by crosslinking and sufficiently available for hydration [38,39]. According to the water band analysis of the IR spectra, water HB strength proved to be comparable to or higher than those in bulk water.…”

“…In a similar way, theπ-HBH is stabilized by cations because the acceptability of water protons, or AN of water, may be enhanced via ionic hydration. These stabilization schema have been, in fact, supported by different kinds of experimental data, such as ab initio calculation for the HBH to the phenol's acidic proton [37], T 2 values of water proton from NMR measurements for the hydrogel [38], and analysis of water and hydrations of the polymer segment in gel phase by FT-IR spectroscopy [39].…”

Magnetic Resonance Microscopy for Assessment of Morphological Changes in Hydrating Hydroxypropylmethylcellulose Matrix Tablets In Situ–Is it Possible to Detect Phenomena Related to Drug Dissolution Within the Hydrated Matrices?

“…It is clear that if the interactions between water and the polymer matrix are getting stronger, the crystallization temperatures will be decreasing. The non-freezable bound water absorbed in polymer does not crystallize as a typical exothermic peak, even when the swollen sample is cooled down to −70°C ( 16 ).…”