Plastic pollution and resource waste are urgent issues of global concern, and scientists are working hard to find sustainable and green alternatives to conventional plastics. Traditional thermosets form permanent and inflexible networks once cured. They are difficult to recycle and eventually turn into pollutants. However, thermosets prepared using dynamic covalent chemistry (DCC) can be used like normal thermosets, but their networks are constructed through reversible chemical bonds that can break and reform in certain conditions. Thus, these thermosets have unique properties including reusability, recyclability, degradability, and self-healing capabilities. These characteristics align with the "3Rs" of sustainability: reduce, reuse, and recycle. Therefore, DCC has been considered as a promising solution to the plastic pollution.

Over the past decade, many dynamic polymer materials have been developed using DCC such as transesterification, transalkylation, transamination, and the Michael addition reaction. However, these dynamic reactions endow polymers with adaptive networks, but only a few other functions. To achieve dynamic materials with advanced features, several reactions have to be combined with DCC, making the design and synthesis process complex. This hinders the broad application of DCC in developing high-value functional polymer materials.

Our group is not only interested in the mechanical properties of polymers but also in their functions. We hope to find dynamic chemistry with unique functions. We believe that exploring dynamic reactions based on molecular structures that have intrinsic functions are important for the development of DCC. Thus, identifying functional groups that can also participate in dynamic reactions is key.

In nature, reversible chemistry based on functional heterocycles plays a central role in biological regulation. A well-known example is the reversible methylation and demethylation of DNA and RNA. Enzyme-catalyzed m⁵C methylation and demethylation proceed systematically under mild conditions, and the critical heterocyclic basic groups serve different genetic functions before and after the methylation (Fig. 1a). We are inspired by this natural reversible process, and develop a new strategy called heterocycle-based dynamic covalent chemistry (H-DCC).

Heterocyclic compounds have many important functions and play essential roles in material science, biological science, and the medical field. However, dynamic reactions based on the functional heterocycle are rarely exploited for the development of dynamic polymer materials. In this work, we propose a dynamic reaction based on the 3,4-dihydropyrimidin-2(1H)-thione (DHPMT) heterocycle (Fig. 1b).

Fig. 1 | Nature-inspired heterocycle-based dynamic covalent chemistry (H-DCC). a, Reversible m⁵C DNA/RNA methylation process in nature. b, Heterocycle-based dynamic covalent chemistry (DHPMT as a typical example) developed in this work.

We chose DHPMT for several reasons:

• Some aza-Michael addition reactions are reversible; thus, the efficient aza-Michael addition reactions between DHPMT and electron-deficient olefins may be reversible under carefully screened conditions, although their reversibility has not yet been reported.
• DHPMT derivatives have many useful properties, such as anti-ultraviolet (UV), anti-bacterial, anti-viral, and anti-oxidation. If we could confirm the reversibility of their reactions, we could use them to create functional dynamic materials.
• DHPMT derivatives can be facilely prepared via the famous three-component Biginelli reaction using accessible substrates; thus, the target dynamic materials can be prepared with tunable functions and at low synthetic costs.

In this study, we uncovered, for the first time, the reversibility of the aza-Michael addition between DHPMT and electron-deficient olefins, opening the door to a new type of DCC. Using this reaction, we successfully prepared crosslinked polymer with excellent reprocessability and self-healing property (Fig. 2a), similar with those formed via conventional DCC. The exciting finding is that we could also take advantage of DHPMT’s intrinsic functions to create materials with UV protection capacity (Fig. 2b) and tunable luminescence properties (Fig. 2c), which is difficult to achieve using common DCC. Our findings show that H-DCC is not only a viable route to making dynamic polymer networks, but also a powerful strategy for developing dynamic functional materials easily.

Fig. 2 | Dynamic functional materials via the H-DCC. a, Reprocessing, reshaping, and self-healing properties of the materials (scale bar=0.5 cm). b, UV-light blocking performance and wear resistance of the materials. c, Tunable fluorescence properties of the materials.

As a proof-of-concept study, this work opens a new path in polymer chemistry and dynamic chemistry. It highlights the importance of exploring functional heterocycles as dynamic building blocks to overcome the limitations of traditional DCC. In future work, we aim to extend this strategy to other heterocycles and further expand the structures and functions of the polymers made via H-DCC.

With growing demand for diverse applications, multifunctionality, and sustainable development in polymer materials, we believe our study offers a fresh synthetic strategy to construct advanced polymer materials. We hope this work will spark innovation in DCC and prompt DCC and dynamic functional materials into the real applications.