Exclusive One-Way Cycle Sequence Control in Cationic Terpolymerization of General-Purpose Monomers via Concurrent Vinyl-Addition, Ring-Opening, and Carbonyl-Addition Mechanisms

Cationic terpolymerization of vinyl ether (VE), oxirane, and ketone successfully proceeded via unprecedented concurrent vinyl-addition, ring-opening, and carbonyl-addition mechanisms. In particular, the use of cyclohexene oxide as an oxirane resulted in terpolymerization via an exclusive one-way cycle, i.e., the reactions occurred only in the VE → oxirane, oxirane → ketone, and ketone → VE directions. Terpolymers that have repeating units of (VE_∼2–oxirane_∼2–ketone)_<i>n</i> were obtained under appropriate conditions. In addition, no two-monomer combination achieved efficient copolymerization, which suggests that three specific types of crossover reactions are required for successful terpolymerization. The presence of a ketone, a compound that has rarely been employed as a monomer, is indispensable for a one-way cycle: terpolymerization also proceeded with an aliphatic aldehyde but resulted in two-way crossover reactions at the aldehyde-derived propagating ends

Concurrent Cationic Vinyl-Addition and Ring-Opening Copolymerization Using B(C₆F₅)₃ as a Catalyst: Copolymerization of Vinyl Ethers and Isobutylene Oxide via Crossover Propagation Reactions

Alkyl vinyl ethers and isobutylene oxide were concurrently copolymerized through cationic vinyl addition and ring opening using B­(C₆F₅)₃ as a catalyst. NMR analyses and acid hydrolysis of the products demonstrated that the copolymerization successfully proceeded through crossover reactions between vinyl and cyclic monomers to yield multiblock-like copolymers. Appropriate catalyst and monomer combinations with suitable reactivities were key for copolymerization

Controlled Cationic Copolymerization of Vinyl Monomers and Cyclic Acetals via Concurrent Vinyl-Addition and Ring-Opening Mechanisms

Vinyl monomers and cyclic acetals were demonstrated to copolymerize with sufficient crossover propagation reactions in a controlled manner via the generation of long-lived species. Such unusual propagation reactions, mediated by the active species derived from different types of monomers, were shown to require an appropriate dormant–active equilibrium, achieved via the elaborate design of the initiating systems. The controlled copolymerization of 2-chloroethyl vinyl ether (CEVE) and 1,3-dioxepane (DOP) proceeded using SnCl₄ as a catalyst in conjunction with ethyl acetate and 2,6-di-<i>tert</i>-butyl­pyridine, yielding multiblock-like copolymers as a result of several rounds of crossover reactions per chain. Under the same conditions, when 2-methyl-1,3-dioxolane (MDOL) was used instead of DOP, the polymerization proceeded in a highly controlled manner and involved more frequent crossover reactions. In addition, MDOL underwent almost no homopropagation reactions, unlike DOP. The nature of the cyclic acetal-derived propagating species is most likely responsible for the difference in the copolymerization behavior. Long-lived species were also generated in the copolymerization of styrene and 1,3-dioxolane (DOL), although measurable amounts of cyclic oligomers were produced via backbiting reactions

New Degradable Alternating Copolymers from Naturally Occurring Aldehydes: Well-Controlled Cationic Copolymerization and Complete Degradation

Three naturally occurring conjugated aldehydes, (1<i>R</i>)-(−)-myrtenal, (<i>S</i>)-(−)-perillaldehyde, and β-cyclocitral, were cationically copolymerized with isobutyl vinyl ether using the EtSO₃H/GaCl₃ initiating system in the presence of 1,4-dioxane as an added Lewis base. Alternating copolymerization proceeded exclusively via 1,2-carbonyl addition of the aldehydes. In addition, controlled alternating copolymerization was achieved under appropriate reaction conditions, producing copolymers with controlled molecular weights and narrow molecular weight distributions. The relationships between the copolymerization behaviors and the cyclic side group structures of the aldehydes suggested that conjugated and bicyclic structures were important factors for controlled alternating copolymerization. However, too much bulkiness around the carbonyl group resulted in termination of copolymerization. The resulting alternating copolymers were stable under neutral and basic conditions. In sharp contrast, mild acidic conditions degraded the alternating copolymers almost selectively to conjugated aldehydes with low molecular weights as nearly single products

Alkoxyoxirane, a Unique Cyclic Monomer: Controlled Cationic Homopolymerization Mediated by Long-Lived Species and Copolymerization with Vinyl Ether via Alkoxy Group Transfer

1-Methoxy-2-methylpropylene oxide (MOMPO), an alkoxyoxirane that can generate a carbocation adjacent to an alkoxy group via ring-opening, was demonstrated to polymerize in a controlled manner with the use of a metal chloride as a Lewis acid catalyst. The choice of the initiating system is critical for the successful controlled homopolymerization of this alkoxyoxirane; a GaCl₃/THF system was observed to be the best combination for the initiating system. Furthermore, the copolymerization of MOMPO with isopropyl vinyl ether (IPVE) generated long-lived species when CF₃SO₃H/<i>n</i>Bu₄NI was used as the initiating system. Surprisingly, the reaction proceeded via the transfer of the alkoxy group in the IPVE unit. More specifically, the isopropoxy group at the penultimate IPVE unit transferred to the MOMPO-derived propagating cation after the crossover reaction from the IPVE-derived carbocation to MOMPO. This type of reaction creates a side group that possesses the ring-opened MOMPO structure with the isopropoxy group. The generation of copolymers via the “alkoxy-group transfer” mechanism is unique to the copolymerization in this study and was confirmed by ¹H, ¹³C, and 2D NMR analyses and by the acid hydrolysis and subsequent reacetalization reactions of the products

Quantitative and Ultrafast Synthesis of Well-Defined Star-Shaped Poly(<i>p</i>‑methoxystyrene) via One-Pot Living Cationic Polymerization

Exceptionally fast and quantitative synthesis of star-shaped poly­(<i>p</i>-methoxystyrene) [poly­(pMOS)] with a well-defined structure was achieved using the one-pot “arm-first” polymer-linking method through base-assisting living cationic polymerization. Star polymers with low polydispersity (<i>M</i>_w/<i>M</i>_n ∼ 1.3) were obtained in a short period of time (homopolymerization time ≤ 0.5 min, polymer-linking time ≤ 3 min) by the reaction of living poly­(pMOS) (DP = 48–285) with an analogous divinyl compound using EtAlCl₂/SnCl₄ dual catalysts in CH₂Cl₂ in the presence of ethyl acetate. The structure of the divinyl compounds and the reaction conditions used for the linking reactions are key to the highly controlled quantitative synthesis. The effect of the arm-chain length of the star-shaped polymer on their thermal properties, evaluated by differential scanning calorimetry, differed from that of the linear polymers. The morphology of the individual star-shaped polymers was also investigated using atomic force microscopy

Synthesis of Highly Defined Graft Copolymers Using a Cyclic Acetal Moiety as a Two-Stage Latent Initiating Site for Successive Living Cationic Polymerization and Ring-Opening Anionic Polymerization

The synthesis of well-defined graft copolymers with designed intervals between branches was achieved using cyclic acetal moieties as two-stage latent initiating sites. A cyclic acetal was shown to initiate the living cationic polymerization of vinyl ethers (VEs), yielding a polymer with a hydroxy group at the α-end derived from the cyclic acetal. The newly generated hydroxy group was able to efficiently induce the subsequent ring-opening anionic polymerization of l-lactide (LLA), and a diblock copolymer with a narrow molecular weight distribution (MWD) was obtained. For the synthesis of a graft copolymer, a five-membered cyclic acetal moiety was introduced at the ω-chain ends of poly­(VE)­s, which was employed as the initiating site for the living cationic polymerization of VEs. Repeated polymerization and acetalization generated a macroinitiator with several hydroxy groups on the side chain of a poly­(VE) backbone. Graft copolymers possessing branches with narrow MWDs and regular spaces between the branches were synthesized by the ring-opening polymerization of LLA using this macroinitiator

Tandem Reaction of Cationic Copolymerization and Concertedly Induced Hetero-Diels–Alder Reaction Preparing Sequence-Regulated Polymers

A unique tandem reaction of sequence-controlled cationic copolymerization and site-specific hetero-Diels–Alder (DA) reaction is demonstrated. In the controlled cationic copolymerization of furfural and 2-acetoxyethyl vinyl ether (AcOVE), only the furan ring adjacent to the propagating carbocation underwent the hetero-DA reaction with the aldehyde moiety of another furfural molecule. A further and equally important feature of the copolymerization is that the obtained copolymers had unprecedented 2:(1 + 1)-type alternating structures of repeating sequences of two VE and one furfural units in the main chain and one furfural unit in the side chain. The specific DA reaction is attributed to the delocalization of the positive charge to the side furan ring

Well-Defined Polymeric Ionic Liquids with an Upper Critical Solution Temperature in Water

An upper critical solution temperature (UCST)-type phase separation in water was achieved using well-defined polymeric ionic liquids (ILs) with imidazolyl groups in their side chains, prepared based on living cationic polymerization using a cationogen/Et_1.5AlCl_1.5 initiating system with 1,4-dioxane as an added base. Aqueous solutions of the polymers with tetrafluoroborate as counteranions showed sharp and reversible UCST-type phase separation at 5–15 °C. The effect of polymer concentration, chain-end groups, and molecular weight on the phase separation temperature suggests that the phase separation resulted from interpolymer electrostatic interactions. Other polymeric ILs with SbF₆^– also showed a lower critical solution temperature-type phase separation in various organic solvents