Alcohol Moiety-Tethering Acylazides as Versatile Isocyanate Precursors for Polymerization Initiators and Monomers

We have developed alcohol moiety-containing stable acylazides as isocyanate precursors that can be employed as polymerization initiators and monomers. Living ring-opening polymerization of δ-valerolactone was initiated by 4-hydroxymethylbenzoylazide (1) in the presence of diphenyl phosphate as a catalyst under mild conditions to afford a polyester possessing the acylazide-functionalized initiation end. After the protection of the terminal OH group of the polyester, Curtius rearrangement of the acylazide moiety triggered by heating generated an isocyanate-terminated polyester quantitatively. Simple heating of 1 at 110 °C efficiently yielded in situ an alcohol–isocyanate compound acting as an AB-type monomer, which produced the corresponding polyurethane in 79% yield via a Lewis acid-catalyzed polyaddition. A pyridine moiety-containing acylazide also underwent a catalyst-free polyaddition to afford the corresponding polyurethane in 88% yield, performing a similar polyurethane synthesis in the presence of an isocyanate-containing polyester; moreover, it afforded a polyester–polyurethane block copolymer, emphasizing the versatility of alcohol moiety-containing stable acylazides.