Studies on the Functional Polysaccharides. (Part 2). Cyanoethylation of pullulan and some physical properties of products.

Abstract

A water soluble polysaccharide, pullulan was cyanoethylated using acrylonitrile in the presence of sodium hydroxide. The reaction conditions which gave the highest DS of 2.7 were the following: sodium hydroxide concentration, 6%; reaction temperature, 60°C and reaction time, 120min. If the reaction conditions were severer than the above conditions, i.e., higher sodium hydroxide concentration, higher reaction temperature and/or longer reaction time, either the elmination of cyanoethyl group or the formation of acrylonitrile homopolymer was observed. The relatively low DS of 2.7 may be interpreted based on the fact that in pullulan molecules the reactive primary hydroxyl groups at C-6 take part in the backbone linkages. Another possible reason would be the influence of their higher ordered structure and also conceivable steric hindrance. The cyanoethylated pullulan dissolved completely in DMSO, and dissolved almost in DMF and dichloromethane, but the solution in the latter solvent was significantly colored. Thermal decomposition temperatures were remarkably affected by the DS: 227.0°C for DS 1.99 and 262.8°C for DS 2.72. The higher DS resulted in the higher thermal decomposition temperature.