Powder-to-powder polycondensation of natural saccharides. Facile preparation of highly branched polysaccharides

Abstract

Solid-state polycondensation of a natural saccharide was found to take place in the presence of H₃PO₄ (5 mol%) at 110 °C under a N₂ flow, giving a highly branched polysaccharide (conv. 11–84%, M_w = 1400–19 000, M_n = 1200–3700); the reaction mixture was powdery throughout the polymerization. Interestingly, α- and β-anomers showed different polymerization behaviour; the former was polymerized more slowly, however, they gave comparable molecular weight polymers. The polysaccharide product was per-O-methylated and subjected to structure analyses. The acid-hydrolysis products, the partially O-methylated monosaccharides, suggested that the polysaccharide products have highly branched structures. MALDI-TOF mass analysis revealed that intramolecular glycosylation and acetal exchange reactions are involved in the polymerization mechanism.