Four Different Regioisomeric Polycarbonates Derived from One Natural Product, D-Glucose
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2016 American Chemical Society. 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--d-glucopyranoside or methyl -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 (Tg) 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 Tg of ca. 85 and 83 C, respectively, as compared to those with 1,4- and 1,6-backbone connectivity, showing a Tg of ca. 33 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 (Td,onset) at 363 or 336 C, as compared with those polymers containing the anomeric carbon in the carbonate linkage (1,4- and 1,6-), having Td,onset at 171 and 163 C.
