Mastering Macromolecular Architecture by Controlling Backbiting Kinetics during Anionic Ring-Opening Polymerization

Defined macromolecular architecture using anionic ring-opening copolymerization (ROcP) of lactones and cyclic carbonates offers facile routes toward copolymers with unique material properties, ranging from thermoplastic to elastomeric. However, monomers with a slow ROP rate are hampered by competing backbiting reactions, scrambling the macromolecular sequence, and, thereby, a loss of material properties occurs. We here solve this issue by controlling the rate of backbiting. Through our approach, we show how block structures previously inaccessible can be synthesized from monomers with vastly different ROP rates, covering small lactones and even including macrolactones. This control can also be extended beyond block structures to include random and gradient architectures by tuning monomer concentration to the relative ROP and backbiting rate.