Photo-Controlled Tandem Polymerization Enabled by a Dinuclear Salen-Al Catalyst for Multiblock Copolymer Synthesis

Expanding tandem polymerization beyond two mutually compatible cycles remains a formidable challenge, largely due to the stringent specificity required by most (photo)catalysts. Here, we report a dinuclear aluminum salen complex bridged by a trithiocarbonate linker that exhibits a unique intramolecular photoinduced energy/electron transfer (PET) process with fast kinetics. This catalyst enables a bidirectional chain propagation pathway and bridges vinyl monomers PET-RAFT polymerization with epoxides/anhydrides ring-opening copolymerization (ROCOP), racemic lactide ring-opening polymerization (ROP), and step-growth polymerization between in situ generated Al-O active species and diisocyanates. Under visible-light regulation, PET-RAFT polymerization exhibits selective on-off switching and can proceed concurrently or in tandem with ROCOP and ROP, whereas ROP occurs only after complete consumption of the anhydride in ROCOP. Leveraging the tandem nature of these four reactions under a single catalytic regime, we achieve the unprecedented one-pot synthesis of (ABCBA)_n multiblock copolymers. This approach establishes a versatile platform for constructing complex macromolecular architectures via multiple tandem polymerizations in a single reaction vessel.