Modular Synthesis of ABAC-Type Periodic Terpolymers via RAFT Single-Unit Monomer Insertion and RAFT Step-Growth Polymerization

Precise control over monomer sequence in synthetic polymers remains a central challenge in polymer chemistry, with significant implications for materials design and controlled degradation. Here, we report a modular and efficient strategy for synthesizing ABAC-type periodic terpolymers by integrating reversible addition–fragmentation chain transfer single-unit monomer insertion (RAFT-SUMI) with RAFT step-growth polymerization. Sequence-regulated oligomers are first constructed via RAFT-SUMI using bifunctional RAFT agents and vinyl monomers, then employed as bifunctional RAFT agents for step-growth polymerization with complementary vinyl monomers. The method enables precise control over polymer sequence and architecture, affording terpolymers with tunable molecular weights and thermal properties. A broad library of ABAC-type terpolymers was synthesized, exhibiting glass transition temperatures ( T g ) from −28.75 to 79.75 °C and decomposition temperatures ( T d ) from 194.9 to 243.64 °C. Incorporation of disulfide linkages into the polymer backbone further enabled selective degradation in response to chemical stimuli, confirming the periodic nature of the sequence. This work establishes a generalizable platform for constructing precision macromolecules with programmable functionality, offering broad potential for applications in degradable materials and advanced polymer systems.