POLYSACCHARIDES FROM THERMAL POLYMERIZATION OF GLUCOSIDES

As a first step towards synthesis of labeled polysaccharides for studies of mechanisms of pyrolysis, the acid-catalyzed thermal polymerizations of methyl α-d- and phenyl β-d-glucopyranosides have been studied and the optimum yields of polymer determined. The phenyl aglycone is a more facile leaving group than methyl and hence the phenyl glucoside yields polymer more rapidly at lower temperature. However, the byproduct phenol is less rapidly removed than methanol during polymerization, and the polysaccharide products from the phenyl glucoside are less pure. The polymer from methyl α-d-glucopyranoside is a mixed glucopyranan of average degree of polymerization (d.p.) 10-13, as determined by three different methods. The end groups are methyl α-d-glycopyranoside units, the predominant in-chain linkage, determined by methylation analysis, is 1→6, and the predominant branch points are 3,6-linked. Both α- and β-glucopyranosidic linkages are present in-chain in the approximate ratio 2:1. The similar, acid-catalyzed thermal polymerization of 1,6-anhydro-β-d-glucopyranose (levoglucosan, LG) has also been studied, and the mechanisms of the polymerizations are discussed. © 1990.