Sequence-Controlled Polyhydroxyurethanes with Tunable Regioregularity Obtained from Sugar-Based Vicinal Bis-cyclic Carbonates
Résumé
The carbonation of biosourced 1,2-diols is a sustainable avenue for the synthesis bis-five-membered cyclic carbonates (bis-5CCs), the precursors of a valuable class of polymers, for example, polyhydroxyurethanes (PHUs). In this work, we performed the direct carbonation of optically pure sugar-based butadiene tetraols, namely, (i) meso-erythritol and (ii) its (S,S) diastereoisomer, (L)-threitol. The corresponding vicinal bis-5CCs, erythritol dicarbonate (EDC) and threitol dicarbonate (TDC), respectively, retain the stereochemistry of the starting tetraols. The comprehensive study of their aminolysis reaction, in DMSO and at room temperature, indicates that the kinetics and the regio-orientation of the ring opening of the 5CC are very much dependent on their stereochemistry. The total aminolysis of EDC results in the formation of hydroxyurethanes with an excess of secondary hydroxyl groups, (OH)II, of about 85%, against 60% for TDC. Moreover, when considering the two consecutive aminolyses of EDC (and TDC, respectively), the kinetic rate constant of the first aminolysis k1,EDC (and k1,TDC, respectively) is 1 order of magnitude higher than that of the second aminolysis, k2,EDC ∼ k1,EDC/10 (and k2,TDC ∼ k1,TDC/10, respectively). We used this feature to develop a one-pot, two-step polymerization procedure, offering sequence-controlled PHUs. All the experimental results are well supported by density functional theory calculations. In the end, the comparative study of these two diastereoisomers of simple sugar-based vicinal bis-5CCs provides a new family of PHUs with tunable sequence- and regioregularities.
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