Interpretation of the polyelectrolyte and antipolyelectrolyte effects of poly(N‐vinylimidazole‐co‐sodium styrenesulfonate) hydrogels

Abstract

Hydrogels of N‐vinylimidazole (VI) and sodium styrenesulfonate (SSS) were synthesized in aqueous solution by radical crosslinking copolymerization with N,N′‐methylene‐bis(acrylamide) as crosslinker. Swelling in several saline solutions was measured for hydrogel samples synthesized with different comonomer concentrations (CT = 10, 25, or 40%) and with SSS mole fractions covering a broad range (fSSS = 0–0.7), while the crosslinker ratio was 2 wt % in all cases. The degree of swelling in aqueous solution with a specific ionic strength (μ), plotted versus the SSS composition of the feed, shows a minimum for any set of samples synthesized with a fixed CT. The dependence of swelling on μ shows both polyelectrolyte (fSSS beyond the minimum) and antipolyelectrolyte behaviors (in the low fSSS limit). It was found that the nonGaussian factor of the crosslinking density and the polymer‐solvent interaction parameter increase with fSSS for any CT. Moreover, in the low fSSS limit, the osmotic swelling pressure is governed not only by the ionic contribution, but also by the polymer‐solvent mixing and, the concentration of mobile counterions inside the gel is not proportional to the net fixed charge but to the addition of cationic and anionic side groups, what discards the formation of ionic pairs. The antipolyelectrolyte effect is interpreted as due to the increasing protonation of VI as μ goes up. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1683–1693, 2007

Discrimination of the roles of crosslinking density and morphology in the swelling behavior of crosslinked polymers: Poly(N‐vinylimidazole) hydrogels

“…The affine model and gaussian chains were considered for P el . 22,24,31 Equation (5), with 16 v ¼ 0.496 þ 0.308v 2 , affords the m e (S) values plotted in Figure 5 for PVI swollen in deionized water.…”

“…To obtain v in acid solutions, the protonation of the imidazole rings and the subsequent ionic contribution to the osmotic swelling pressure must be considered 22,24 and thus, it results that v ¼ (0.547 AE 0.008) þ (0.01 AE 0.07)v 2 , for PVI swollen in HCl aqueous solution with pH i ¼ 4, which corresponds to a degree of protonation within the range 0.0121 AE 0.0005.…”

“…Protonation converts neutral polymers in polyelectrolytes showing particularly interesting effects [22][23][24][25] in which the roles of morphology and crosslinking are imbricated. In this work, both neutral and protonated PVI hydrogels were studied.…”

Enhanced Absorbent Products Incorporating Cellulose and Its Derivatives: A Review

“…The tendency of polyelectrolyte complexes and polyampholyte systems to swell with water upon addition of salt has been called the "antipolyelectrolyte effect" (Valencia and Pierola 2007;Dogu et al 2009;. Because this effect appears to be consistent with the behaviour of the hemicellulose-based PECs just described, some background will be given here.…”

“…As an underlying explanation for the effect, it has been shown that the addition of salt tends to weaken the electrostatic interactions within a PEC (Dragan and Cristea 2001). Increased absorbency with increasing salinity of aqueous solutions has been observed in several cases in which oppositely charged polyelectrolytes were employed in the preparation of cellulose-or hemicellulose-based hydrogels (Paula et al 2002;Feng and Pelton 2007;Valencia and Pierola 2007;Shang et al 2008;Salam et al 2011a,b;Gawel et al 2012). Such weakening of the pair-wise associations of ionic groups on the polymer chains allows a partial reversal of the process…”