Mineto Uchiyama

Living anionic polymerization is a powerful tool for precision polymer synthesis, but typically requires highly reactive organometallic initiators and stringent conditions. Recently, we developed proton transfer anionic polymerization (PTAP) of acrylic monomers, which proceeds via reversible proton transfer reactions between growing anionic species and dormant C–H bonds, offering a milder and more user-friendly alternative. Herein, we report PTAP of 2-vinylpyridine (2VP), an aromatic vinyl monomer with a lower reactivity than acrylic monomers, to expand the scope of PTAP systems. Controlled anionic polymerization of 2VP was achieved using compounds with weakly acidic C–H bonds as initiators or chain-transfer agents (CTAs) in the presence of potassium tert -butoxide as base catalysts with cryptand 222 or 18-crown-6 as ligands. Systematic investigations revealed that appropriate CTAs and slow monomer addition were effective for achieving precise molecular weight control. Additionally, this system also exhibited tolerance to tert -butyl alcohol, which functioned as a reversible terminator to rapidly regenerate dormant C–H species and to enable more precise molecular weight control. Furthermore, the facile synthesis of poly( N , N -diethylacrylamide)- b -poly(2VP) block copolymers was successfully achieved by sequentially conducting PTAP of acrylic and aromatic vinyl monomers on the basis of common dormant C–H bonds.

The carbonyl group is an abundant and fundamental functional group in chemistry. While carbonyl compounds have been polymerized via anionic and cationic mechanisms, their radical polymerization remains challenging. In this study, we report the radical copolymerization of formaldehyde (FA), an abundant and important C1 resource, and vinyl acetate (VAc) to generate novel vinyl copolymers that contain C–O bonds in their backbones. The polymerization of VAc in the presence of commercially available paraformaldehyde (PFA) as an FA source produced poly(FA-co-VAc)s via the addition of VAc radicals to the carbon side of FA and the subsequent addition of alkoxy radicals to VAc, resulting in the –CH₂O– units in the backbone. This reaction pathway was supported by NMR analyses and DFT calculations. The incorporation of FA was increased to 22% when polar solvents with highly protic and hydrogen-donating natures were used, which increased the concentration of FA generated from PFA in situ. Saponification of the poly(FA-co-VAc)s produced novel poly(vinyl alcohol) (PVA) copolymers with main-chain oxygen atoms and unique thermal properties. In addition, the detailed structure of the resulting copolymers was analyzed by reacetylation of the poly(FA-co-VA)s. This study highlighted the potential of radical polymerization of the C═O bond to generate unprecedented polymers with oxygen atoms in the backbones.

Growing concern over marine- and microplastic pollution has intensified the need for efficient polymer upcycling strategies. Herein, we report a family of iridium complexes bearing a PNNP tetradentate ligand, ((PNNP)Ir), as a versatile prototypical platform for the hydrogenative depolymerization of polyesters. Systematic modification of the bipyridine and phosphine substituents enables the conversion of a broad range of polyesters, including commodity plastics, into diols under mild and even solvent-free conditions. Notably, selective semi-hydrogenation of poly(ethylene terephthalate) (PET) is achieved through fine-tuning of the (PNNP)Ir framework. While fully hydrogenative depolymerization proceeds via direct H₂ addition, semi-hydrogenation operates through a H2-free, transfer-hydrogenation pathway. As a result, (PNNP)Ir complexes can utilize diverse hydrogen sources, and both reaction modes are readily extended to deuteration. These findings establish (PNNP)Ir as an exceptionally versatile and pertinent scaffold for the upcycling of polyesters into value-added chemical feedstocks.

Understanding the degradation of polymeric materials is central to sustainable material design, yet the fate and properties of degraded products, i.e., oligomers, remain poorly understood. In this work, we report the synthesis and biodegradability assessment of discrete oligomers of poly-(butylene succinate), poly-(ethylene terephthalate), polyamide 6 (Nylon-6), and polyisoprene. Using iterative synthesis approaches, we obtained well-defined discrete oligomeric species with precise end-group structures for each polymer. Accelerated marine biodegradability analysis revealed distinct degradation behaviors depending on the polymer class and molecular weight. These findings underscore the importance of investigating oligomeric degradation products to better understand the fate of discarded polymers and to guide the rational design of environmentally benign materials.

In this work, we found a new class of controlled/″living″ polymerization system, which proceeds bidirectional fashion using click reaction of AB monomer bearing azide and alkyne functionalities in a single molecule. The click polymerization of the AB monomer proceeded well using both azide and alkyne initiators in a well-controlled manner in either growth direction to afford polymers with predetermined molecular weights and narrow molecular weight distributions, as well as the terminal structures inherited from the initiator. Especially, the polymerizations with the difunctional initiators provided well-defined linear polymers with azide or alkyne groups at both termini. This approach also allows for polymerization control over the second monomer to give a block copolymer.

Dual-degradable poly(vinyl ether)s were prepared by cationic degenerative chain-transfer copolymerization of macrocyclic thioacetal carbonate and vinyl ether and degraded to low- and controlled-molecular-weight products by acid and base catalysts.

Monodisperse amphiphilic diblock oligomers of C16 alkyl chains and vinyl alcohol units were prepared by aldol-group transfer polymerization and recycling size-exclusion chromatography separation to form a double-crystalline lamellar structure.

In this work, we found a new class of controlled/"living" polymerization system, which proceeds bidirectional fashion using click reaction of AB monomer bearing azide and alkyne functionalities in a single molecule. The click polymerization of the AB monomer proceeded well using both azide and alkyne initiators in a well-controlled manner in either growth direction to afford polymers with predetermined molecular weights and narrow molecular weight distributions as well as the terminal structures inherited from the initiator. Especially, the polymerizations with the difunctional initiators provided well-defined linear polymers with azide or alkyne groups at both termini. This approach also allows for polymerization control over the second monomer to give a block copolymer.

Dual control of the molecular weight and tacticity in proton transfer anionic polymerization (PTAP) of methyl methacrylate (MMA) was investigated by using various ligands in the presence of a bulky potassium base catalyst and an organic compound with a weakly acidic C-H bond as dormant species in toluene at 0 °C. The tacticity of the resulting poly(MMA) (PMMA) produced without ligands was nearly atactic (rr/mr/mm = 22/54/24). However, the use of 18-crown-6 as a ligand afforded predominantly syndiotactic PMMA (rr ≈ 58%), whereas the use of chiral bis(oxazoline) ligands gave slightly isotactic-rich PMMA (mm ≈ 32%). Molecular weight control of PMMA was achieved (Đ = 1.1-1.2) by adding 1,1-diphenylethanol as a reversible terminator while maintaining control of the tacticity with the above ligands. Stereoblock PMMA consisting of atactic and syndiotactic segments was successfully synthesized via sequential PTAP using macroinitiator/macro-CTA methods.

Living anionic polymerization—the most common living polymerization and the one with the longest history—generally requires stringent, water-free conditions and one metal initiator per polymer chain. Here we present the proton transfer anionic polymerization of methacrylates using acidic C–H bonds as the dormant species that are activated by base catalysts. The polymerization mechanism involves reversible chain transfer or termination of the growing enolate species. A weakly acidic compound, such as an alkyl isobutyrate, serves as the initiator or chain-transfer agent in the presence of a bulky potassium base catalyst to produce a polymer chain and, thereby, diminishes the metal compound per chain ratio. An added alcohol serves as a reversible terminator to tame the propagation. End-functionalized, star, block and graft polymers are easily accessible from compounds with C–H bonds.