Alternating Cationic Copolymerization of Vinyl Ethers and Aryl-Substituted Cyclic Acetals: Structural Investigation of Effects of Cyclic Acetals on Copolymerizability

The effects of the structural difference of cyclic acetals were investigated in the cationic copolymerization with vinyl monomers via the concurrent vinyl-addition and ring-opening mechanisms. A series of alkyl- and aryl-substituted cyclic acetals were successfully copolymerized with 2-chloroethyl vinyl ether (CEVE) under appropriate conditions. In particular, copolymerization of an aryl-substituted 2-(4-methoxyphenyl)-1,3-dioxolane (PMPDOL) with CEVE involved exclusive crossover reactions between PMPDOL and CEVE, resulting in alternating copolymers. Copolymerization of PMPDOL and other vinyl ethers and styrene derivatives also proceeded via the frequent crossover reactions, while the copolymerization of 2-methyl-1,3-dioxolane, a methyl-substituted counterpart of PMPDOL, with vinyl monomers except for CEVE proceeded negligibly. The difference in the substituents of cyclic acetals significantly affected the electronic and steric environments around the carbocation generated in the propagation reaction, which is related to the frequency of the crossover reaction. Acid hydrolysis of alternating copolymers resulted in complete degradation and selective generation of a single compound due to the periodic incorporation of acetal structures in the main chains, which supported the well-defined structure of copolymers. The monomer reactivity ratios were also consistent with the copolymerizability difference between the aryl- and alkyl-substituted cyclic acetals. The structure–polymerizability relationship of cyclic acetals in the copolymerization was discussed based on the reaction mechanism during the propagating reaction

ABC-Type Periodic Terpolymer Synthesis by a One-Pot Approach Consisting of Oxirane- and Carbonyl-Derived Cyclic Acetal Generation and Subsequent Living Cationic Alternating Copolymerization with a Vinyl Monomer

A one-pot synthesis of ABC-type periodic terpolymers with controllable molecular weights was achieved via an elaborately designed method consisting of sequence-programmed cyclic monomer synthesis and living cationic copolymerization of this cyclic monomer with a vinyl monomer. In this method, a cyclic acetal generated by a selective and quantitative Lewis acid-catalyzed cyclodimerization reaction of an oxirane and a carbonyl compound was subjected to subsequent copolymerization without any isolation or purification. Alternating copolymerization of the cyclic acetal and vinyl ether (VE) proceeded, yielding an ABC-type periodic terpolymer composed of oxirane, a carbonyl compound, and VE. Interestingly, the copolymerization proceeded in a living manner, which allowed simultaneous control of the molecular weight, molecular weight distribution, and chain ends in addition to the periodic sequence. Moreover, the terpolymers could be degraded by acid due to the periodically located acetal moieties. The use of various monomers also produced ABC-type sequence terpolymers. ABC-b-ABD-type periodic block quaterpolymers were synthesized by the sequential addition of vinyl monomers during the living copolymerization. These results surely provide a simple and efficient approach for the design of monomer sequences, polymer lengths, and chain ends in synthetic polymers

Sequence-Controlled Polymer Synthesis Derived from Alcohols, Cyclic Enol Ethers, and Vinyl Ethers: Selective Generation of 2‑Alkoxy Cyclic Ethers Followed by Living Cationic Alternating Copolymerization by the One-Pot Process

Syntheses of sequence-controlled copolymers with controllable molecular weights and chain ends composed of alcohols, cyclic enol ethers, and vinyl ethers (VEs) were demonstrated using an approach consisting of selective monomer generation and subsequent alternating copolymerization. Acid-catalyzed additions of alcohols to 2,3-dihydrofuran or 3,4-dihydro-2H-pyran proceeded quantitatively to yield 2-alkoxy cyclic ethers (2-ACEs). Subsequent cationic alternating copolymerization of the 2-ACE and a VE proceeded successfully via concurrent ring-opening and vinyl-addition mechanisms, yielding copolymers with periodically arranged alcohol-derived side chain-containing cyclic enol ether and VE moieties in the repeating units. Complete degradation of the obtained copolymers into a single compound by alcoholysis confirmed the alternating sequences. The use of 2-propanol, (−)-menthol, and (1R)-endo-(+)-fenchyl alcohol was effective for the syntheses of well-defined polymers, whereas the use of methanol resulted in oligomers. The bulkiness of the alkoxy groups of the 2-ACEs likely contributed to the preference for propagation rather than chain transfer

Chiral Single-Chain Magnet: Helically Stacked [Mn^III₂Cu^II] Triangles

The one-dimensional complex [Mn^III₂Cu^II(μ₃-O)­(Cl-sao)₃(EtOH)₂]·EtOH (Mn₂Cu) was obtained by the metal replacement reaction of the trinuclear manganese complex (Et₃NH)­[Mn^III₃(μ₃-O)­Cl₂(Cl-sao)₃(MeOH)₂(H₂O)₂] with [Cu­(acac)₂]. The Mn₂Cu chain exhibits single-chain-magnet behavior with finite-size effects due to its large magnetic anisotropy