Thermal polycondensation of sugar fluoride to form highly branched polysaccharide

\Sugar fluorides were found to undergo powder-to-powder polycondensation without any catalyst at 110-160 degrees C under vacuum, giving highly branched polysaccharides (Conv. = 40-95%, M-w = 1400-20,000). The cross-polarized optical microscopy at 110 degrees C disclosed that the crystal shape of alpha-glucosyl fluoride (FG1c) was unchanged throughout the polymerization in spite of producing the amorphous polymer (Poly-FiGle). The solid-state post polymerization of Poly-FIGIc (Mw: 2700) at 180 degrees C increased the higher molecular weight (Mw: 8900). The product polysaccharide was per-O-methylated and subjected to structure analyses. Acid-hydrolysis, which gave a variety of the partially O-methylated monosaccharides, suggested that the product polysaccharides had a highly branched structure consisting of all of the possible glycosidic linkages. MALDI-TOF mass analysis revealed that the 1,6-anhydride terminal unit was formed and participated to the polymerization. Interestingly, amaltosyl fluoride hydrate (FMal.H2O) was polymerized at the lower temperature (100 degrees C) than the anhydrate (FMal), which required 160 degrees C for the polymerization. They produced different structure polymers even from the same monomer. The polymer from the former consisted of the disaccharide-repeating unit, while the repeating unit of the polymer from the latter was the monosaccharide, which was formed by the acetal exchange reaction. (C) 2007 Wiley Periodicals, Inc.