Metal-Free, Photoinitiated Cationic Terpolymerization of Vinyl Ethers, Oxiranes, and Ketones: Simultaneous Control of Monomer Sequence and Molecular Weight by the Formation of Long-Lived Propagating Species

Simultaneous control of multiple factors, such as the molecular weight, sequence, initiation reactions, chain ends, and topology, related to polymers and polymerization reactions, is highly desirable to achieve the sophisticated and precise design of polymers. In this study, we aimed to develop a novel polymerization system by combining sequence-controlled, living, and photoinitiated polymerization reactions. As a result of fine-tuning the reaction conditions, including the monomer combinations and additives, the photoinitiated, sequence-controlled cationic terpolymerization of vinyl ether (VE), oxirane, and ketone proceeded in a living manner to yield polymers with predetermined molecular weights and ABC pseudo-periodic sequences. By using a diaryliodonium salt as a photoinitiator, terpolymerization was initiated via UV irradiation without any metal-based catalysts or corrosive protonic acids. During terpolymerization, the following highly selective crossover reactions occurred: VE -> oxirane, oxirane -> ketone, and ketone -> VE. Moreover, dormant species were generated from the oxirane-derived propagating end and a suitable cyclic ether, resulting in propagation reactions that proceeded in a living manner. The generation of these dormant species was confirmed by oxirane homopolymerization in the presence of cyclic ethers and terpolymerization quenching using sodium phenoxide as a quencher.