Synthesis of ABC-Type Periodic Terpolymers through a Reversible Lock–Unlock Mechanism in Living Carbanionic Polymerization

Precise sequence control in polymer synthesis remains a paramount challenge in contemporary macromolecular engineering and requires the development of innovative methodologies. Herein, we report a reversible “Lock–Unlock” mechanism in living carbanionic polymerization, achieved through the ingenious design of the surrounding structure of carbanions, enabling the synthesis of ABC-type periodic terpolymers. Nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) simulations demonstrate that the bridged-ring steric hindrance in 5-methylene-10,11-dihydro-5H-dibenzo[a,d][7]annulene (MDDAE) induced the formation of a half-enclosed carbanion structure in MDDAE-Li. Notably, MDDAE-Li exhibits unique monomer-selective copolymerization characteristics, undergoing nucleophilic reactions with 1-phenyl-1,3-butadiene (1-PB) but not with styrene (St). Therefore, 1-PB acts as a molecular “key” unlocking MDDAE/St copolymerization. Leveraging this monomer-selective behavior of MDDAE-Li, we established a reversible “Lock–Unlock” ternary copolymerization system (MDDAE/1-PB/St) that achieves precise ABC-type periodic terpolymers. Reversibility of the “Lock–Unlock” switch is governed by 1-PB consumption during ternary copolymerization (MDDAE/1-PB/St)-polymerization halts at 1-PB depletion and resumes upon its reintroduction. These significant findings not only enhance the mechanistic understanding of living anionic polymerization but also establish a theoretical framework for synthesizing sequence-defined copolymers.