13C Solid State NMR determination of crosslinking degree in super-absorbing cellulose based networks

C-13 solid-state NMR analysis has been performed on microporous superabsorbing networks based on hydroxyethylcellulose and sodium salt of carboxymethylcellulose in order to determine the chemically effective cross-linking degree. Microporous samples characterized by two different degrees of cross-link have been analyzed by performing C-13 cross-polarization magic angle spinning (CP-MAS) solid-state spectra and single-pulse excitation (SPE) experiments. Cross-linking degrees, expressed as number of cross-links per monomer, have been evaluated from the area of resonance due to methylene carbon atoms present on reacted cross-linker molecule (divinyl sulfone) and area of resonances due to anomeric carbon atoms C-l of the polysaccharide rings. Optimization procedures for both CP-MAS and SPE experiments are also reported.