Synthesis of Hyperbranched Polysaccharide by Thermally Induced Cationic Polymerization of 1,6-Anhydro-β-d-mannopyranose

Abstract

The thermally induced cationic polymerization of 1,6-anhydro-β-d-mannopyranose (1) as a latent cyclic AB4-type monomer was carried out using 2-butenyltetramethylenesulfonium hexafluoroantimonate (2) as the initiator. The solution polymerization in propylene carbonate proceeded without gelation to produce the water-soluble hyperbranched polysaccharides (3) with controlled molecular weights and narrow polydispersities. The weight-average molecular weight (Mw,SLS) values of 3 measured by static laser light scattering (SLS) varied in the range 6.5 × 103 to 6.4 × 105, which were significantly higher than the weight-average molecular weight (Mw,SEC) values by size exclusion chromatography (SEC). The viscosity of the solution of 3 was very low, and the intrinsic viscosities were from 0.032 to 0.047 dL·g-1. Polymer 3 was composed of α- and β-linked hyperbranched polysaccharides consisting of 19 kinds of d-mannopyranosyl and d-mannofuranosyl repeating units, which had numerous nonreducing d-mannopyranosyl terminal units. The degree of branching (DB), estimated by the methylation analysis of 3, was in the range of 0.38−0.44. The thermally induced cationic polymerization of 1 using 2 is a facile method leading to the hyperbranched polysaccharide with a high DB value.