Abstract
A new series of 1, 4-anhydro-3-azido-ribopyranose derivatives was synthesized as functional monomers in order to study effects of the monomer structure on selective ring-opening polymerization behaviors and structures of the resulting polysaccharides. The general formula of the four monomers were written as 1, 4-anhydro-3-azido-3-deoxy-2.O-(p-substituted benzyl)-α-D-ribopyranose (A3A2SBR), in which the substituted group represented methyl (CH3), hydrogen (H), chloro (CI), and bromo (Br) group. The four monomers were synthesized by reaction of 1, 4-anhydro-3-azido-3-deoxy-2-O-acetyl-α-D-ribopyranose with p-substituted benzyl chlorides or bromides. Selective ring-opening polymerization of the monomers was performed by BF3•OEt2 catalyst at -20°_??_40°C to give 3-azido-3-deoxy-2-O-(p-substituted benzyl)-(1→5)-α-D-ribofuranans with _??_n of 1.7×104_??_4.6×104and[α]D20of+180.1_??_+217.2°. Ring-opening polymerization by SbCl5 catalyst at-40°C afforded a polymer composed of a mixture of 1, 5-α-and 1, 5-β-ribofuranosidic units. In the selective ring-opening polymerization by BF3•OEt2 catalyst, _??_n increased and molecular weight distributions _??_n/_??_w became narrower with changing Hammett sigma constant of the p-substituted groups from negative to positive values in following order: methyl (-1.4), hydrogen (0), chloro (+2.4) and bromo (+2.6) groups. It was revealed that the p-substituted groups with different Hammett sigma constants had a regular effect in the ring-opening polymerization.
