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Our recent results in the concurrent cationic vinyl-addition and ring-opening copolymerization of vinyl ethers (VEs) and oxiranes are summarized with particular emphasis on the strategies required to generate crossover reactions between different types of monomers. Most importantly, carbocation generation via the ring-opening reaction of the oxonium ion is indispensable for the crossover reaction from oxirane to VE. This article also summarizes concurrent cationic vinyl-addition, ring-opening and carbonyl-addition terpolymerization, the copolymerization using an alkoxyoxirane through the alkoxy group transfer mechanism and the long-lived species-mediated polymerization using cyclic formals.

Monomer sequence transformation and reversible polymerization–depolymerization control were achieved in the cationic copolymerization of 2-methyl-1,3-dioxepane and γ-butyrolactone by vacuuming or temperature change. The removal of monomers from the polymerization solution with a vacuum pump promoted depolymerization, resulting in a transformation to pseudo-alternating copolymers and subsequent oligomer formation. Heating the polymerization solution also promoted a similar monomer sequence transformation and oligomer formation, while cooling led to the polymerization of monomer molecules generated via depolymerization.

An initiating system composed of GaCl₃ and an alkylbenzene was demonstrated to be highly effective for the controlled cationic polymerization of a plant-derived monomer, β-pinene. When two equivalents of hexamethylbenzene were added to GaCl₃ in conjunction with 2-chloro-2,4,4-trimethylpentane as an initiator, cationic polymerization of β-pinene successfully proceeded in a living manner at –78 °C. Successful control over the reaction was attributed to the formation of a complex between GaCl₃ and the alkylbenzene, as confirmed by UV–vis and ⁷¹Ga NMR analyses.

Amphiphilic block copolymers poly[(2-ethoxyethyl vinyl ether)-block-(2-methoxyethyl vinyl ether)] (EOVE-b-MOVE) induce the ring assembly of silica nanospheres (SNSs, ca. 15 nm) in the liquid phase. Nanorings form with appropriate polymer concentration, pH and temperature. EOVE-b-MOVEs with varying block lengths successfully induce the ring assembly of SNSs, whereas a random copolymer fails, indicating that polymer’s molecular structure critically affects the assembly mode of SNSs. Interestingly, SNSs of a larger size (ca. 30 nm) one-dimensionally assemble into nanochains with these block copolymers under otherwise identical conditions.

Highly efficient synthesis of heteroarm star-shaped polymers containing independent stimuli-responsive moieties was demonstrated using a one-pot arm-linking method via base-assisting living cationic polymerization. The linking reaction of mixed two or more kinds of living polymers with a divinyl compound successfully yielded heteroarm star polymers with narrow molecular weight distributions. Furthermore, this methodology was expanded to polar functional monomers, producing a heteroarm star-shaped polymer with amino-containing and thermosensitive arms. The obtained heteroarm star-shaped polymers exhibited their unique stimuli-responsive behaviors in water or their film surfaces.

The effect of polymer design on the interfacial structure and physical properties of polymer films in water based on a poly(vinyl ether) platform with hydrophilic side-chains was examined to construct bioinert interfaces. Hydrophilic surfaces were prepared by utilizing the preferential segregation of a rubbery component in a diblock copolymer film with a glassy component, crosslinking a hydrophilic polymer, and designing an interfacial modifier with a special architecture. Interfacial structure and physical properties controlled by polymer design play important roles in determining bioinert properties.

Cationic polymerization of p-methylstyrene (pMeSt) was examined using various metal chlorides as Lewis acid catalysts in dichloromethane. Polymerization using SnCl₄ and ZnCl₂ in conjunction with 2,6-di-tert-butylpyridine (DTBP) proceeded in a controlled manner in contrast to the reactions with metal trichlorides, including AlCl₃, FeCl₃ and GaCl₃. In addition, the combination of SnCl₄ and DTBP allowed the controlled polymerization of less reactive styrenes and the synthesis of star-shaped poly(pMeSt)s through the cross-linking reaction using an alkylstyrene-type divinyl compound.

Our recent studies on the polymerization of diazocarbonyl compounds to afford functional polymers are reviewed. In the first part of this article, Pd-mediated polymerization of various functionalized diazoacetates and unique properties of the resulting polymers due to the effects of the dense packing of the functional groups in the polymers are described. The second part of this report summarizes our recent results on the polycondensation of bifunctional diazocarbonyl compounds as monomers.

This review focuses on the controlled radical polymerization of vinyl ether (VE) and the related self-assemblies. VE was long believed to be among the monomers that could not be radically homopolymerized. Under such circumstances, some groundbreaking polymerizations of VE have been discovered. Advances in research have made it possible to perform controlled radical polymerization with VE due to hydrogen bonds and/or cation-π interactions between VE monomers and the propagating radical. By using the resulting poly(VE)s, various functional polymers and nano-objects via polymerization-induced self-assembly can be obtained.