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

Abstract

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.

Sugar-Derived Cyclic Acetals as Comonomers for Cationic Copolymerization with Vinyl Ethers

“…The coordinating ability of the anions is likely related to this order, although there is no definitive scale of coordinating ability as far as we know. − The weaker interaction between the propagating cation and counteranion is most likely advantageous for easier access of the sugar-derived cyclic acetals to the propagating cation, resulting in more frequent crossover reactions when initiators or catalysts that generate counteranions with weaker coordinating ability were used. The influence of counteranions on crossover frequency was also observed in our recent study on cationic terpolymerization of VE, oxirane, and ketone; however, a reason for such influences is unclear. From the results of the copolymerization of CEVE and E-1 using Ph 3 CB­(C 6 F 5 ) 4 , the monomer reactivity ratios of CEVE and E-1 were determined to be 5.0 (CEVE) and approximately 0 (E-1) (Figure S19 and Table S4; by the Meyer–Lowry method , ), which were consistent with the nonhomopolymerizability of E-1.…”