Synthesis of Hyperbranched 2,5-Anhydro-d-glucitol by Proton-Transfer Cyclopolymerization of 1,2:5,6-Dianhydro-d-mannitol

The cyclopolymerization of 1,2:5,6-dianhydro-d-mannitol (1) was carried out using BF3·OEt2 and t-BuOK. Although the anionic polymerization tended to form gels, the cationic polymerization proceeded through the proton-transfer reaction mechanism to produce hyperbranched carbohydrate polymers (2) mainly consisting of 2,5-anhydro-d-glucitol units. The weight-average molecular weight (Mw,SLS) values of 2 measured by static light scattering (SLS) varied in the range of 2.08 × 105−26.9 × 105, which were significantly higher than the weight-average molecular weight (Mw,SEC) values by size exclusion chromatography (SEC). The degree of branching (DB), estimated by the 13C NMR measurements, was ca. 0.44−0.46. The α value of the Mark−Houwink equation, which was determined by the viscosity measurements, was ca. 0.3. The hyperbranched polymers 2 were nanoscale particle with the radii of gyration (Rg) of 67.4−132.0 nm.