Borane Lewis Pair-Mediated Ring-Opening Polymerization of Epoxides: Direct Access to α-Acyl Azide/ω-Hydroxyl Heterotelechelic Polyethers and Latent Isocyanate Derived Polyurethane

Abstract

Heterotelechelic polyethers bearing two orthogonally addressable end groups are attractive precursors for modular macromolecular construction, yet their direct synthesis remains challenging when one terminus contains a highly reactive latent functionality such as an acyl azide. Herein, we report a borane Lewis pair-mediated strategy for the controlled ring-opening polymerization (ROP) of propylene oxide (PO) using 4-hydroxymethylbenzoyl azide as a bifunctional initiator precursor. In the presence of the multiborane Lewis acid POSS-B8 and phosphazene base tBuP2, polymerization proceeded under bulk conditions at 25 °C to afford α-acyl azide/ω-hydroxyl-terminated poly(propylene oxide)s (PPOs) with targeted molecular weights from 0.5 to 10.0 kg/mol. The acyl azide end group remained intact throughout polymerization, enabling the direct preparation of well-defined heterotelechelic polyethers without post-polymerization end-group modification. Subsequent thermolysis triggered Curtius rearrangement to generate the corresponding α-isocyanate/ω-hydroxyl PPOs, which underwent self-polyaddition to yield polyurethane materials without the use of external diisocyanates. This approach integrates controlled epoxide polymerization with latent end-group activation and provides a concise route to functional PPOs and isocyanate-free-feed polyurethane synthesis.