Organocatalyzed ROP of a Glucopyranoside Derived Five-Membered Cyclic Carbonate

Saccharides, based on their wide bioavailability, high chemical functionality and stereochemical diversity, are attractive starting materials for the development of new synthetic polymers. Established carbonylation methodologies were used to synthesize a 5-membered cyclic carbonate monomer, 4,6-O-benzylidene-2,3-O-carbonyl-alpha-D-glucopyranoside (MBGC), in high yield (>95%) from a commercially available D-glucopyranoside derivative. The ability of this monomer to undergo ring opening polymerization (ROP) with a range of organocatalysts, rather than the previously reported anionic initiators, was investigated. These new conditions were developed to widen the functional group tolerance in the polymerization, and achieve better control over the final properties of the polymers. The most promising of the catalysts examined, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), was used in a kinetic study to confirm the well-controlled nature of the ROP. Optimized conditions were then successfully applied to the synthesis of polymers of different molecular weights. Two post-polymerization modifications were completed via the removal of the benzylidene acetal protecting group to release a water-soluble poly(glucose carbonate), and then addition of acetyl groups to facilitate characterization studies. MALDI-TOF MS analysis was performed to further probe the chemistry of the polymerization and deprotection. A wide range of thermal decomposition temperatures (233-347 degrees C), glass transition temperatures (87-233 degrees C), and water contact angles (38-128 degrees) was achieved by this series of polymers. The hydrolytic degradability of these polymers was also examined, demonstrating differing degradation mechanisms based on the acidic vs. basic conditions used. Consequently, this single monomer was successfully employed in the straightforward synthesis of a polymeric system with tunable properties based on the molecular weight and repeat unit composition.