Microstructural Examination of Semi-Interpenetrating Networks of Poly(N,N-dimethylacrylamide) with Cellulose or Chitin Synthesized in Lithium Chloride/N,N-Dimethylacetamide

Semi-interpenetrating networks (SIPNs) of poly(N,N-dimethylacrylamide) (DMAm) containing cellulose or chitin were prepared in 9%LiCl/N,N-dimethylacetamide (DMAc) as the homogeneous reaction medium. N,N-Methylenebisacrylamide (MBAm) was utilized as the cross-linking agent with 2,2‘-azobisisobutyronitrile (AIBN) as the initiator. The respective SIPNs contained 25, 12, and 6 wt % cellulose or 6 wt % chitin. A control DMAm hydrogel (without polysaccharide) was also synthesized in 9%LiCl/DMAc. The 25 wt % cellulose DMAm SIPN was found to be unique, differing from the other compositions prepared, possessing a 6-fold higher modulus than the DMAm control. The enhancement in mechanical stiffness was attributed to intimate molecular interactions and complexation between cellulose and DMAm. The presence of the extended cellulose chains within the DMAm matrix creates a more open network in the nonsolvated state as reflected in DSC and fluorescence experiments. It is this molecular level interaction of cellulose with DMAm that enhances the physical properties in the first SIPN composite to utilize unmodified cellulose and chitin. In the solvated state, the microdispersed polysaccharide hydrogen bonds with the DMAm matrix increases the rigidity of the network yet allows reversible hydration as reflected in rheology, equilibrium swelling, and fluorescence experiments.