ABSTRACT
Dextran synthesis by Schuerch in 1966 made an epoch in the field of the synthesis of natural polysaccharides which had not succeeded for a long time. The high molecular weight polysaccharide with the controlled backbone linkage and the complete stereoregularity, which arc two major characteristics of natural polysaccharides, has been successfully synthesized by ring-opening polymerization of an anhydro sugar. It is reasonable to consider that when the polymerization is completed the polymer chain scission and depolymerization can further occur in the presence of PF5. This phenomenon has also been observed in the polymerization of a 1,4-anhydro-ribose derivative. Therefore, it may be concluded that the reactivity of unsubstituted 1,6-anhydro sugars is the same as that of perbenzylated 1,6-anhydro sugars. Although the homopolymerizability of the 1,6-anhydro-mannose monomer is the highest of the four 1,6-anhydro sugars, it is not the case of the copolymerization.
