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.