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Contemporary macromolecular chemistry and physics offer interesting options for making, characterizing and manipulating single polymer chains. Although it is not yet possible to emulate the structural control and functional ability of biopolymers, recent advances have opened up interesting avenues for applications of these synthetic systems in microelectronics, photovoltaics, catalysis and biotechnology.

Cyclopolymers have potentially interesting molecular recognition properties due to their in-chain multiple rings. Here, the authors report cation-templated, controlled radical cyclopolymerization of poly(ethylene glycol) dimethacrylates, yielding polymeric pseudo-crown ethers with large in-chain cavities.

The ultimate control in polymer synthesis, precise monomer sequencing, is a highly sought after but complex problem. Here, the authors employ a repetitive and iterative intramolecular cyclization reaction, via a radical intermediate, to generate sequence-controlled vinyl oligomers.

The metal-catalyzed living radical polymerization has now been developed diversely in terms of the catalytic systems, controllable monomers, well-defined polymer structures and combinations with stereospecific radical polymerization. This review describes a short overview of recent developments in metal-catalyzed living radical polymerization mainly focusing on our recent research studies related to the subject.

Two neutral ligands, carbonyl and phosphine, were cooperatively incorporated into half-metallocene iron(II) complexes [CpFeBr(CO)(PR₃)] for more active and versatile systems in transition metal-catalyzed living radical polymerization. Among the CpFeBr(CO)(PR₃) complexes examined, CpFeBr(CO)(PMePh₂) showed the highest activity and the best controllability, and the ‘living’ character of the polymerizations therewith was proved by sequential monomer-addition experiments. In spite of the high activity, the Fe(II) complex is stable and robust enough to be handled under air, rendering it suitable for practical use.

A pentamethylcyclopentadienyl (Cp*)-based ruthenium complex with phenolic phosphine ligands 4-(hydroxyphenyl)diphenylphosphine ([PPh₂(pPhOH)]) showed a high catalytic activity for aqueous living radical polymerizations of hydrophilic methacrylates (for example, poly(ethylene glycol) methacrylate (PEGMA), 2-hydroxyethyl methacrylate (HEMA) and so on). Importantly, the activity was high enough to control the aqueous polymerizations even with just catalytic amount. Such an advanced catalysis would be caused not only by a simple hydrophilicity of the ligand but also by a water-assisted dynamic transformation from the original saturated form [Cp*RuCl(PR₃)₂; 18e; PR₃=phosphine] into an unsaturated but active one [Cp*RuCl(PR₃); 16e] upon which water molecule(s) may additionally coordinate for further stabilization.

This review is focused on evolutions of precision radical polymerizations in various directions from metal-catalyzed Kharasch addition or atom transfer radical addition (ATRA). The developments include metal-catalyzed living radical polymerizations via reversible activation of carbon-halogen bonds, metal-catalyzed step-growth radical polymerizations of designed monomers having an unconjugated vinyl group and a reactive carbon-halogen bond, simultaneous metal-catalyzed chain- and step-growth radical polymerization for producing degradable vinyl copolymers with main-chain ester units, and vinyl monomer sequence control via combinations of iterative ATRAs and various controlled polymerizations.

The development of reversible-deactivation radical polymerization (RDRP) has made a great contribution not only to control of molecular weight and terminal structures but also to precise syntheses of copolymers. In particular, introducing a new concept into RDRP allows ‘sequence control’, which might lead to construction of ‘alphabet polymer’ bearing well-defined sequence like peptides in nature. Herein, some methodologies to realize sequence control based on RDRP are reviewed.

Poly(ethylene glycol)-armed Ru(II)-bearing microgel star polymers, directly obtained from ruthenium-catalyzed living radical polymerization, were used as catalysts for transfer hydrogenation of ketones in 2-propanol. Owing to the good affinity of the core-reaction pocket and the surrounding arms to substrates and products, respectively, the star polymer catalysts homogeneously hydrogenated various ketones into the corresponding alcohols more efficiently than the other polymer-supported catalysts and the original ruthenium counterpart. The catalyst encapsulation into the unique microgel core further afforded efficient catalyst recycle and facile product recovery.

Single-chain crosslinked star polymers with hydrophilic and thermoresponsive poly(ethylene glycol) short arms and a hydrophobic core were created as novel microgel star polymers of single polymer chains via the intramolecular crosslinking of self-folding amphiphilic random copolymers in water. For this, well-controlled amphiphilic random copolymers bearing hydrophobic olefin pendants were synthesized as self-folding precursors by ruthenium-catalyzed living radical polymerization and the subsequent introduction of olefin units. The copolymers with 20–40 mol% hydrophobic units efficiently gave single-chain crosslinked star polymers in water.

This article reviews the design of polymeric functional spaces with microgel-core star polymers and single-chain folding/crosslinked polymers via living radical polymerization for unique functions. Core-functionalized star polymers were prepared by the intermolecular linking of arm polymers with functional linkers/monomers to provide solubilized microgel spaces for active and recyclable catalysis and selective and stimuli-responsive molecular recognition. Single-chain folding and crosslinked polymers were in turn obtained from the self-folding and/or intramolecular linking of amphiphilic random copolymers carrying hydrophilic poly(ethylene glycol) chains and hydrophobic alkyl pendants in water.

This focus review discussed our recent developments of unnatural glycopolymers based on polyoxazoline, protein–polymer conjugates, and protein stabilization. To develop new glycopolymers, a bicyclic monomer composed of glucosamine and 2-methyl-2-oxazoline (MeOx) was designed. This cationic ring-opening polymerization proceeded not by the mechanism for MeOx but by a new polymerization mechanism. This oligosaccharide has promise to be applied to a new glycomaterial owing to the polymer design. Additionally, protein conjugation and encapsulation by amphiphilic/fluorous chain-folding nanoparticles were investigated. Fluorous nature in random copolymers was useful for the protein conjugation and stabilization.

This focused review is an overview of recent research on bio-based polymers produced by the controlled/living polymerization of naturally occurring or derived renewable monomers, such as terpenes, phenylpropanoids and itaconic derivatives. The judicious choice of initiating system, such as controlled/living cationic or radical polymerization, which was borrowed from conventional petrochemical monomers, not only allowed the polymerization to proceed efficiently but also produced well-defined bio-based polymers with high performance from these renewable monomers.

To develop highly functional gel materials, the precision construction of the network structure is required. This focus review outlines the structural design of polymer gels by utilizing precision radical polymerization techniques with a focus on the authors’ recent research. In particular, the synthesis of homogeneous networks using precise radical polymerization and the control of the swelling characteristics by tuning the monomer sequence in the gel network chain are described.

Partially crosslinked poly(diphenylacetylene) (3a) bearing silanol groups were synthesized by the treatment of the membrane of 2a with n-Bu₄N⁺F⁻. Imidazolium salt-containing poly(diphenylacetylene) (3b (Br⁻)) was obtained by the substitution of 1-methylimidazole to the membrane of 2b. Sulfonation of 2c gave a sulfonated poly(diphenylacetylene) (3c). The membrane of 3a was found to exhibit high gas permeability irrespective of the presence of the polar silanol groups in the polymer. Introduction of 1-methylimidazole into the membrane remarkably increased the CO₂/N₂ selectivity (P_CO2/P_N2=31–44). The sulfonated polymer 3c exhibited high CO₂ permselectivity, and the P_CO2/P_N2 was as large as 54.