MICROSTRUCTURAL EXAMINATION OF SEMIINTERPENETRATING 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 of chitin were prepared in 9%LiCl/N,N-dim ethylacetamide (DMAc) as the homogeneous reaction medium. N,N-Methylen ebisacrylamide (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 DM Am hydrogel (without polysaccharide) was also synthesized in 9%LiCl/DM Ac. The 25 wt % cellulose DMAm SIPN was found to be unique, differing from the other compositions prepared, possessing a 6-fold higher modul us 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 wit hin the DMAm matrix creates a more open network in the nonsolvated sta te as reflected in DSC and fluorescence experiments. It is this molecu lar level interaction of cellulose with DMAm that enhances the physica l properties in the first SIPN composite to utilize unmodified cellulo se and chitin. In the solvated state, the microdispersed polysaccharid e hydrogen bonds with the DMAm matrix increases the rigidity of the ne twork yet allows reversible hydration as reflected in rheology, equili brium swelling, and fluorescence experiments.