Comprehensive analysis of the substituent distribution in 3-O-ethyl/propyl cellulose derivatives

Two 3-O-ethyl-3-O-propyl celluloses of similar ethyl and propyl content prepared under different conditions were analyzed with respect to their substituent distribution in the glucosyl units and along the polymer chain by ESI-MS analysis of labeled oligosaccharides. Both samples showed similar regioselectivity of substitution and random distribution of ethyl and propyl groups over the 3-O-positions. The distribution of all types of glucosyl residues identified by monomer analysis was also random over the cellulose molecules. Comparison of the substitution pattern in the glucosyl units with the pattern expected for the observed regioselectivity showed relative high 2-O-alkylation in spite of protecting group strategy, but no corresponding 2,3-di-O-substitution. This is probably the result of partial silyl migration under the alkaline alkylation conditions.