Cationic Single-Unit Monomer Insertion (cSUMI): From Discrete Oligomers to the α-/ω-End and In-Chain Sequence-Regulated Polymers.

Single-unit monomer insertion (SUMI) has become an important strategy for the synthesis of sequence-controlled vinyl polymers due to its strong versatility and high efficiency. However, all reported SUMI processes are based on a free-radical mechanism, resulting in a limited number of monomer types being applicable to SUMI or a limited number of sequences of structural units that SUMI can synthesize. Herein, we developed a novel SUMI based on a cationic mechanism (cSUMI), which operates through a degenerative (similar to radical SUMI) but cationic chain transfer process. By optimizing the chain transfer agent (CTA) and monomer pairs, a high-efficiency cSUMI was achieved for vinyl ether and styrene monomers. Based on this reaction, a range of discrete oligomers containing vinyl ether and styrene moieties, and even α-/ω-end and in-chain sequence-regulated polymers were synthesized, most of which cannot be achieved by radical SUMI. In addition, we explored the application of these sequence-regulated polymers in the preparation of miktoarm star polymers, delivery of photosensitizers, and solubilization of fluorescence probes. The development of SUMI with a new mechanism will certainly broaden the scope of structures and sequences in precise vinyl-based polymers.