The synthesis of novel cellulose and chitin derivatives, membranes, and interpenetrating networks utilizing lithium chloride/N,N-dimethylacetamide

Sheila Louise Williamson


The primary research goal is to develop new polysaccharide-based materials under homogeneous reaction conditions utilizing lithium chloride/N,N-dimethylacetamide. Polysaccharide derivatives, polysaccharide membranes, and polysaccharide-containing networks have been synthesized, structurally characterized, and their physical properties have been determined. Cellulose carbamate and ester derivatives were synthesized by reacting cellulose with ethyl 4-isocyanatobenzoate or an activated ester of N,N-dimethylaminobenzoic acid. The isocyanate reactions yielded cellulose derivatives with controllable degrees of substitution and high yields. By contrast, the activated ester reactions resulted in lower degrees of substitution and yields due to undesirable side reactions. Semi-interpenetrating networks (SIPNs) of poly(N,N-dimethylacrylamide) (DMAm) containing cellulose or chitin were prepared utilizing 9%LiCl/N,N-dimethylacetamide (DMAc) as a homogeneous reaction solvent. N,N-methylenebisacrylamide (MBAm) was utilized as crosslinking agent with $2,2\sp\prime$-azobisisobutyronitrile (AIBN) as initiator. The respective SIPNs contained (25, 12, or 6 wt%) cellulose, or 6 wt% chitin. A control DMAm hydrogel (without polysaccharide) was synthesized in 9%LiCl/DMAc. The 25 wt% cellulose DMAm SIPN was found to be unique, differing from the other compositions prepared, possessing a six fold higher modulus than the DMAm control. The enhancement in mechanical strength was attributed to intimate molecular interactions and complexation between cellulose and DMAm as evident from thermal degradation and $\sp{13}$C NMR. The presence of the polysaccharide within the DMAm matrix creates a more open network in the nonsolvated state as reflected in DSC and fluorescence experiments. In the solvated state, the polysaccharide hydrogen bonds with the DMAm matrix to resist swelling and increases the rigidity of the network as reflected in the rheology, equilibrium swelling, and fluorescence experiments. Ionic 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 (6, 12, or 25 wt%) cellulose or (6% wt) chitin were also synthesized in 9% LiCl/N,N-dimethylacetamide (DMAc). Control systems (without polysaccharide) were synthesized in 9%LiCl/DMAc. The swelling behavior of these materials was investigated as a function of pH (DMAEAm networks) or electrolyte concentration (AMPS networks). Surfactant sequestration by the polysaccharide-containing materials was greater than that of the control gels; however, the rates of binding were lower. Release of the bound surfactant was achieved by disrupting the charge-charge interactions contributing to polymer-surfactant interaction by changing the pH of the medium DMAEAm networks) or by the addition of electrolyte (AMPS networks). The DMAm/DMAEAm SIPNs released only 4% of the surfactant originally sequestered while, the DMAm/AMPS SIPNs released approximately 80%.