Arihiro Kanazawa

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.

Biologically synthesized or bioinspired process-derived iron oxides as catalysts for living cationic polymerization of a vinyl ether.

Fe(3)O(4) synthesized by magnetotactic bacteria and α-Fe(2)O(3) synthesized via a microbial-mineralization-inspired process functioned as catalysts for the controlled cationic polymerization of a vinyl ether.

Shape-switching self-assembly of new diblock copolymers with UCST-type and LCST-type segments in water

A dual thermosensitive behavior, i.e., self-assembly at both high and low temperatures, was achieved in water using vinyl ether block copolymers with imidazolium salt side-chains (exhibiting a UCST behavior) and oxyethylene side-chains (exhibiting an LCST behavior). The block copolymers were precisely prepared via living cationic polymerization in the presence of a weak Lewis base. They formed micelles at lower temperatures and vesicles at higher temperatures in water, as confirmed via UV-Vis spectroscopy, dynamic light scattering (DLS), static light scattering (SLS), variable temperature 1H NMR, and fluorescence measurements using pyrene as a polarity-sensitive probe. Furthermore, concentrated aqueous solutions of the block copolymers underwent sol–gel transitions by either raising or lowering the temperature.

Chemically recyclable alternating copolymers with low polydispersity from conjugated/aromatic aldehydes and vinyl ethers: selective degradation to another monomer at ambient temperature

A highly efficient chemical recycling system, involving repetitive cycles of precision synthesis and selective degradation of product copolymers, was developed based on controlled cationic alternating copolymerization of conjugated/aromatic aldehydes, such as cinnamaldehyde (CinA) and (E,E)-5-phenylpenta-(2,4)-dienal (PPDE), via exclusive 1,2-carbonyl addition with vinyl ethers (VEs).

Frequency control of crossover reactions in concurrent cationic vinyl-addition and ring-opening copolymerization of vinyl ethers and oxiranes: specific roles of weak Lewis bases and solvent polarity

Weak Lewis bases and solvent polarity are demonstrated to be highly responsible for the frequency of crossover reactions in the concurrent cationic vinyl-addition and ring-opening copolymerization of alkyl vinyl ethers (VEs) and oxiranes. Weak Lewis bases such as ethyl acetate and 1,4-dioxane promote crossover reactions from isobutylene oxide- or butadiene monoxide-derived propagating species to an alkyl VE monomer, potentially through the more frequent generation of carbocations via the ring opening of the oxonium ion. The specificity of the carbocation that results from the ring-opening reaction—a preference for VE monomers or an aversion to oxirane monomers—is another factor that changes the crossover frequency. Weak Lewis bases, however, have little effect on the relative reactivity of the VE-derived propagating species to each monomer. In contrast, solvent polarity has a significant effect on the promotion of crossover from the VE-derived propagating end to an oxirane, while the frequency of the crossover from the oxirane-derived propagating end is not affected. In contrast to the two oxiranes, the reaction conditions have little effect on the copolymerization using isoprene monoxide, which is an oxirane that generates a more stable, resonance-stabilized carbocation through ring opening. The relative reactivities of VEs and oxiranes under various conditions are discussed in terms of the average number of each monomer unit in one block of the copolymers and in terms of the monomer reactivity ratios.

Sequence-controlled degradable polymers by controlled cationic copolymerization of vinyl ethers and aldehydes: precise placement of cleavable units at predetermined positions

Sequence-controlled degradable polymers with precisely placed breakable bonds in the main chain were synthesized by controlled alternating cationic copolymerization of vinyl ethers (VEs) and aldehydes. Novel linear polymers with acid-labile acetal units derived from VE–aldehyde alternating sequences at predetermined positions were prepared by adding a small amount of p-methylbenzaldehyde during the living cationic polymerization of 2-chloroethyl VE (CEVE). The single addition of a large amount of an aldehyde, myrtenal, during the living polymerization of isobutyl VE (IBVE) produced a block-type copolymer with a completely degradable segment of myrtenal and IBVE. Furthermore, star-shaped polymers that had degradable cores composed of acetal structures were successfully prepared by two methods: addition of (i) a mixture of a bifunctional VE and a monofunctional aldehyde or (ii) a bifunctional aldehyde to the living propagating poly(VE). The resulting polymers with acid-labile units were selectively degraded and transformed into lower MW polymers with other shapes quantitatively under mildly acidic conditions.

In situ and readily prepared metal catalysts and initiators for living cationic polymerization of isobutyl vinyl ether: dual-purpose salphen as a ligand framework for ZrCl4 and an initiating proton source

A salphen complex [salphen = N,N′-o-phenylene-bis(3,5-di-tert-butyl-salicylidene-imine)], synthesized in situ by mixing a salphen ligand with a metal chloride is shown to be an effective catalyst in cationic polymerization for the first time. Furthermore, the salphen/ZrCl4 system induced the living cationic polymerization of isobutyl vinyl ether in toluene at 0 °C with quantitative initiation from HCl simultaneously generated upon the complex formation.

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.

Synthesis of block or graft copolymers containing poly(styrene derivative) segments by living cationic polymerization using acetal moieties as latent initiating sites

Selective acetal-initiated living cationic polymerization was successfully employed for the precision synthesis of block and graft copolymers containing poly(p-methylstyrene) and poly(alkyl vinyl ether) segments. The synthesis involved the living cationic polymerization of p-methylstyrene from the acetal moieties at the chain ends or in the side chains of poly(alkyl vinyl ether). Quantitative initiation of the reaction from the acetal moieties and efficient propagation were achieved via the use of a combined initiating system, TiCl4 and SnCl4, in the presence of ethyl acetate as an added base and 2,6-di-tert-butylpyridine as a proton trap reagent in CH2Cl2 at 0 °C. Appropriate ratios of acetal units, TiCl4, and SnCl4 were indispensable for the quantitative reaction. Solubility and thermal analyses indicated that the properties of the block and graft copolymers were mainly governed by the poly(p-methylstyrene) segments. The synthesis of block and graft copolymers using a more reactive alkoxystyrene was also achieved via the initiation reaction from acetal moieties.

Controlled radical polymerization of styrene with magnetic iron oxides prepared through hydrothermal, bioinspired, and bacterial processes

Controlled/living radical polymerization was examined with the use of magnetic iron oxide (Fe3O4) prepared through various processes, including hydrothermal synthesis, a bioinspired process, and magnetotactic bacteria. Prior to the use of various types of Fe3O4, commercially available Fe3O4 was employed as a heterogeneous catalyst for styrene polymerization in conjunction with an alkyl halide as an initiator. Under appropriately optimized conditions, with the addition of Ph3P in a solvent mixture of toluene and DMF, the polymerization proceeded in a well-controlled manner. In addition, solid Fe3O4 was recovered using a magnetic approach and was reused for a polymerization reaction. The effects of stirring on the polymerization rate suggest that the surface of Fe3O4 is responsible for the catalysis in polymerization. Fe3O4 samples prepared through various processes were then used for styrene polymerization and showed different activities depending on the preparation process. In particular, Fe3O4 prepared through hydrothermal synthesis exhibited a much higher activity compared with commercial Fe3O4.