A versatile method for preparing cyclic polyurethanes

A versatile method was developed to specifically prepare well-defined cyclic polyurethanes based on the combination of a controlled ring-opening polymerization (ROP) of macrocyclic monomers and a self-accelerating double-strain promoted azide-alkyne click ring-closing reaction (DSPAAC). In this approach, the controlled ROP of macrocycles was used to prepare azide-terminated telechelic polyurethanes with controlled molecular weights, narrow dispersities, and sequence-defined and functional backbone structures. The self-accelerating DSPAAC reaction was then used to ring-close the well-defined telechelic polyurethanes with azide terminal groups and prepare the corresponding cyclic polyurethanes using sym-dibenzo-1,5-cyclooctadiene-3,7-diyne (DIBOD) as the small linker. Assisted by slowly feeding a polyurethane solution into a DIBOD solution, this bimolecular ring-closing approach could reach a productivity of ca. 0.8 g/L for the formation of cyclic polyurethanes with varied backbone structures.