Controlled Ring-Opening Polymerization of Macrocyclic Monomers Based on Ring-Opening/Ring-Closing Cascade Reaction

The development of a controlled ring-opening polymerization (ROP) method for synthesizing backbone-functionalized and sequence-controlled polymers with well-defined architectures from macrocyclic monomers is highly desirable in polymer chemistry. Herein, we developed a novel general controlled ROP of macrocycles for producing backbone functional and sequence-controlled polyurethanes and polyamides with controlled molecular weights and narrow dispersities (Đ < 1.1). The key to this method is the introduction of a trimethyl lock unit, an efficient cyclization-based self-immolative spacer, into the macrocyclic monomer ring as a "ring-opening trigger." ROP is initiated by the attack of a primary amine nucleophile on the ring-activated carbonate/ester group, leading to the ring opening of the macrocyclic monomer. Subsequently, spontaneous 6-exo-trig cyclization of the trimethyl lock unit occurs, detaching this ring-opening trigger and regenerating the primary amine end group. The regenerated primary amine group can then be used to propagate the polymer chain by iterating the ring-opening-ring-closing cascade reaction. The versatile ROP method can be applied in the synthesis of water-soluble polyurethanes, backbone-degradable polyurethanes and poly(ester amide)s, and sequence-controlled poly(amino acid)s with well-defined macromolecular architectures.