Four Different Regioisomeric Polycarbonates Derived from One Natural Product, D-Glucose

Strategies for the preparation of polycarbonates, derived from the natural product D-glucose, which have the potential to degrade-back into their bioresorbable starting material and CO2, were developed. By employing established carbohydrate protection/deprotection chemistries, two D-glucose derivatives, methyl 4,6-O-benzylidene-alpha-D-glucopyranoside or methyl a-D-glucopyranoside, were converted into four different regioisomeric diol monomers, i.e., 1,4-, 1,6-, 2,6-, or 3,6-diols, as confirmed by nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, and mass spectrometry. Each type of regioisomeric monomer was then employed in a condensation polymerization with, phosgene, generated in situ from triphosgene, as a comonomer, in the presence of pyridine, to produce four types of polycarbonates with different backbone regio-connectivity, as characterized by size exclusion chromatography, NMR spectroscopy, and IR spectroscopy. Interestingly, their thermal properties, i.e., glass transition temperature (T-g) and thermal degradation behavior, were tunable by changing the topological composition of the monomeric unit. That is, polycarbonates with 2,6- and 3,6 backbone connectivity resulted in significantly higher T-g of ca. 85 and 83 degrees C, respectively, as compared to those with 1,4- and 1,6 backbone connectivity, showing a T-g of ca. 33 degrees C, as measured by differential scanning calorimetry. Furthermore, when the thermal decomposition temperature was measured by thermogravimetric analysis, the nonanomeric carbon backbone-based polycarbonates (2,6- and 3,6-) exhibited higher thermal stability and a sharper decomposition profile, with onset decomposition temperature (T-d,T-onset) at 363 or 336 degrees C, as compared with those polymers containing the anomeric carbon in the carbonate linkage (1,4- and 1,6-), having T-d,T-onset at 171 and 163 degrees C.