One-step synthesis of glucose-branched galactomannan.

The synthesis of branched polysaccharides using naturally occurring materials has been reported since 1975, but applications of branched polysaccharides are relatively limited because of the long and complex modification processes. In this work, a practical and efficient procedure is presented that in one step levoglucosan can be grafted to galactomannan (at 115°C for 15h) with monochloroacetic acid as catalyst. The structural characteristics of the resulting substances were investigated by NMR spectroscopy. The MS (molar degree of substitution) of glucose was shown to gradually increase with the increase of the ratio of levoglucosan to galactomannan, and the maximal MS is 0.6. Levoglucosan units are mostly grafted to the C6-OH of the galactosyl residues in galactomannan, and the maximal percentage of the substituted C6-OH of galactosyl residues is 42.2%. The resulting levoglucosan tended to graft to the branching glucosyl residues of copolymers with an increase in MS, and the average length of the branching glucose is 3.6 when MS is 0.6.