Turning step-growth into chain-growth with click polymerization

A controlled/“living” click polymerization method developed by researchers at Institute of Science Tokyo and Nagoya University enables precise chain-growth of AB-type monomers—traditionally limited to step-growth processes—by leveraging copper-catalyzed azide–alkyne cycloaddition. The approach achieves well-defined polymers with narrow dispersity and enables the bidirectional synthesis of ABA-type block copolymers, offering a powerful new strategy for constructing functional macromolecular architectures from a wide range of monomers.

Traditional polyaddition reactions involving AB-type monomers, which contain both azide and alkyne groups, typically proceed via a step-growth mechanism, forming polymers with triazole rings as the main chain. In such reactions, the reactive molecules (monomers, dimers, or oligomers) can combine randomly with each other, making it challenging to regulate chain length or achieve polymers with desirable structures, a vital requirement for designing polymers with complex and functional architectures.

To address this limitation, a research team led by Professor Kotaro Satoh from Institute of Science Tokyo (Science Tokyo) and Nagoya University, Japan, developed a “controlled/‘living’ click polymerization” system. This method uses click chemistry to drive AB-type monomers to polymerize in a chain-growth fashion, where monomers add selectively to the reactive ends of growing chains—similar to living polymerization—enabling precise control over polymer length and structure. The study was made available online in the Journal of the American Chemical Society on June 13, 2025, and was published on June 25, 2025, in Volume 147, Issue 25.

“We present a novel bidirectional precision polymerization system, enabling controlled chain growth in either direction—an advancement not seen in conventional polymerization methods. This strategy opens new possibilities for creating functionalized polymer,” says Satoh.

The strategy is inspired by the copper(I)-catalyzed azide-alkyne cycloaddition, well-known as the click reaction, in which azide and alkyne groups react with the aid of a copper catalyst to form a stable triazole ring. Bifunctional azide compounds, which contain two azide groups, have been reported to selectively produce molecules with two triazole rings. In this reaction, the first triazole that forms behaves like a ligand, binding to the copper catalyst and creating a reactive site for the formation of the second triazole ring.

To mimic this process, the researchers designed a new polymerization system with initiators, azide- or alkyne-based initiators containing triazole rings and terminal functional groups. These initiators coordinate with the copper catalyst, localizing it near the polymer chain end, and directing monomer addition in a selective and controlled manner.

Using these initiators, the team polymerized an ester-type AB monomer containing azide and alkyne groups under click-reaction-like conditions in dimethylformamide solvent at 20 °C with a copper iodide catalyst. The resulting polymers had long chains with number-average molecular weights (Mn) up to 11,900 and narrow molecular weight distributions (Mw/Mn ≈ 1.1) like conventional living polymerizations, with very few cyclic oligomers as side products. In contrast, without initiators, the reaction produced only short polymers (Mn ≈ 2,000) with a broad size distribution.

The direction of polymer chain growth depended on the type of initiator used. Azide-type initiators began the chain growth from the alkyne end of the monomer, yielding triazole rings with terminal azide groups. Conversely, alkyne-type initiators produced chains ending in alkyne groups.

The reactive end groups on the polymer allowed the researchers to build block copolymers with distinct segments by simply adding new monomers to both ends of a precursor polymer chain.  Starting with a polyester segment (poly(M-1)) bearing two terminal azides, they introduced an amide-type monomer (M-2), whose alkyne groups reacted with azide termini of the M-1 polymer to form an ABA-type triblock copolymer, with polyamide segments on either side of the original polyester block.

By leveraging triazole–copper coordination, this approach provides a new toolset for creating functional, well-defined polymers from a wide range of AB-type monomers. “The presence of azide and alkyne groups appears sufficient to drive polymerization, regardless of the internal structure of the monomer. This flexibility opens up new avenues for the design of complex polymer architectures, which we are now investigating,” says Satoh.  

Overall, the insights gained from this study could be used for developing advanced functional materials, nanostructure designs, and biomedical materials. Let us hope that these findings will revolutionize the area of polymer synthesis.

***

About Institute of Science Tokyo (Science Tokyo)
Institute of Science Tokyo (Science Tokyo) was established on October 1, 2024, following the merger between Tokyo Medical and Dental University (TMDU) and Tokyo Institute of Technology (Tokyo Tech), with the mission of “Advancing science and human wellbeing to create value for and with society.”

END