Hyperbranched 5,6-glucan as reducing sugar ball?

Polymer Chemistry Pub Date: 2009-12-21 DOI: 10.1039/B9PY00223E

Abstract

The ring-opening polymerization of 5,6-anhydro-1,2-O-isopropylidene-α-D-glucofuranose (1) as a latent cyclic AB2-type monomer was carried out using potassium tert-butoxide (t-BuOK) or boron trifluoride diethyletherate (BF3·OEt2) as an initiator in order to synthesize a novel hyperbranched glycopolymer. The anionic and cationic polymerizations proceeded via the proton-transfer reaction mechanism to produce the hyperbranched poly(5,6-anhydro-1,2-O-isopropylidene-α-D-glucofuranose) (2). In particular, the cationic polymerization with the slow-monomer-addition strategy is a facile method leading to the hyperbranched glycopolymers with high molecular weights and highly branched structures. The weight-average molecular weight (Mw,SEC-MALLS) values of 2 measured by multi-angle laser light scattering (MALLS) varied in the range from 7400 to 122?400, which were significantly higher than the weight-average molecular weight (Mw,SEC) values determined by size exclusion chromatography (SEC). The intrinsic viscosities ([η]) of these polymers were very low in the range of 3.3–4.6 mL g?1 and the Mark–Houwink–Sakurada exponents, α, were calculated to be 0.08–0.27. These results of the MALLS, SEC, and viscosity measurements suggested that these polymers exist in a compact spherical conformation in solution because of their highly branched structure. The synthesis of the hyperbranched 5,6-glucan (3) by hydrolysis of polymer 2 was also demonstrated. Polymer 3 is a novel water-soluble hyperbranched glycopolymer arranged with numerous reducing D-glucose units on the peripheries of the polymer, and has a higher reducing ability than D-glucose because of the glyco-cluster effect or the multivalent effect of the reducing D-glucose units. Therefore, polymer 3 should be called a “reducing sugar ball”.

Graphical abstract: Hyperbranched 5,6-glucan as reducing sugar ball
Recommended Literature