A Versatile Approach to ABA‐Type Triblock Copolymers via Mechanistic Transformation from MADIX Process to Photoinduced Free Radical‐Promoted Cationic Polymerization

ABSTRACT In this study, a versatile mechanistic transformation approach was improved for the synthesis of ABA‐type triblock copolymers, featuring polystyrene (PSt) or polyacrylonitrile (PAN) as the central B block and poly(cyclohexene oxide) (PCHO) or poly(butyl vinyl ether) (PBVE) as the terminal A blocks. By integrating MADIX (Macromolecular Design via the Interchange of Xanthates) polymerization with photoinduced free radical‐promoted cationic polymerization (FRPCP), this strategy enables the sequential incorporation of chemically disparate polymer blocks under mild conditions—a combination applied here for the first time to the synthesis of ABA‐type triblock copolymers. The key to this approach lies in a custom‐designed multifunctional xanthate‐based MADIX agent (P‐MXA‐P), which serves both as a chain transfer agent for controlled radical polymerization and as a photoactive initiator for the subsequent cationic photopolymerization. This dual‐functional agent was employed in MADIX polymerization of styrene (St) and acrylonitrile (AN), yielding well‐defined photoactive telechelic polymers, P‐PSt‐P and P‐PAN‐P. Subsequently, these telechelic macrophotoinitiators were successfully transformed into ABA‐type triblock copolymers via photoinduced FRPCP of cyclohexene oxide (CHO) and butyl vinyl ether (BVE). A comprehensive suite of spectroscopic and analytical techniques was employed to elucidate the molecular structures of the synthesized materials, validate block integrity, and demonstrate the broad applicability of this strategy to diverse monomer systems.