Electrolyte and pH responsive surfactant association in ionic semi-interpenetrating networks containing cellulose or chitin synthesized in lithium chloride-N,N-dimethylacetamide

Abstract

Semi-interpenetrating networks (SIPNs) of N,N-dimethylacrylamide (DMAm)–N,N-dimethylamino-ethylacrylamide (DMAEAm), or N,N-dimethylacrylamide (DMAm)–2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) containing cellulose or chitin were synthesized in 9% LiCl–N,N-dimethylacetamide (DMAc). The SIPNs were formulated to contain (1, 2, or 5% w/w) cellulose or 0.8% w/w chitin. Control systems (without polysaccharide) were also synthesized in 9% LiCl–DMAc. An acrylamide (Am)–AMPS hydrogel was synthesized for comparison with the SIPN composites. The swelling behavior of these materials was investigated as a function of pH (DMAEAm-containing networks) or electrolyte concentration (AMPS-containing networks). The DMAm–AMPS materials were found to have higher equilibrium water content (EWC) values in deionized water than the DMAm–DMAEAm materials. The EWC of the DMAm–DMAEAm materials was largest between pH 4 and 5 due to the protonation of the tertiary amine, with the chitin-containing material exhibiting the largest EWC. The DMAm–AMPS materials exhibited a decrease in EWC values with an increase in electrolyte concentration. Polymer–surfactant interactions were shown to exist for surfactants of opposite charge of the ionic mer units incorporated into the polymeric network. Surfactant sequestration by the polysaccharide-containing materials was greater than that of the control gels; however, the rates of surfactant binding were lower. Release of the bound surfactant was achieved by the disruption of the charge–charge interactions by changing the pH of the medium (DMAEAm-containing networks) or by the addition of electrolyte (AMPS-containing networks). The DMAm–DMAEAm SIPNs released only 4% of the surfactant originally sequestered. By contrast, the DMAm–AMPS SIPNs released approximately 80%. The control Am–AMPS hydrogel–surfactant complex collapsed in the presence of electrolyte, and no surfactant was released from the complex. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 989–998, 1999