Alternating copolymerization of l-lactide and ε-caprolactone via enantiomorphic site and chain-end synergistic...

The alternating copolymerization of chiral and achiral cyclic esters, such as commercial l-lactide (l-LA) and ε-caprolactone (CL), remains a significant challenge in polymer synthesis. Here, we introduce an enantiomorphic site and chain-end synergistic control strategy to achieve the first highly alternating copolymerization of l-LA and CL. The polymerization proceeds via a dynamic mechanism: first, the chiral l-LA-terminated chain end and the enantiomorphic site of the catalyst synergistically preclude the homopropagation of highly reactive l-LA; subsequently, the rate-determining insertion of the less reactive achiral CL after the l-LA-terminated chain end, generating an achiral CL-terminated chain end, relieves steric hindrance, which allows the subsequent insertion of highly reactive l-LA. This dynamic control yields highly alternating poly(l-LA-alt-CL) (P _alt up to 0.91). The highly alternating copolymerization of l-ethylglycolide (l-EG) and CL (P _alt = 0.96) further validates the universality of this synergistic control for constructing alternating cyclic ester copolymers.