Abstract
Photoinitiated free radical polymerization (PFRP) is favoured for its simplicity and rapid processing, but typically yields heterogeneous networks with densely crosslinked nanoclusters embedded in a loosely connected matrix, leading to structural weaknesses and mechanical deterioration. Here we incorporate a photocoupling reaction into PFRP systems to convert weakly interconnected nanoclusters into a robust, interlinked network, facilitating effective load transfer between soft and hard phases and enhancing the mechanical properties. This is achieved by partially substituting vinyl moieties with o-nitrobenzyl groups, which generate nitroxides upon photoirradiation with a temporal delay. This allows nanoclusters to form initially, and then enables propagating radicals to couple efficiently within them. Hydrogels synthesized via this approach demonstrate boosted tensile strength up to 20-fold and toughness up to 70-fold compared with PFRP methods, and still gelate within seconds. This strategy demonstrates versatility across various systems and offers a scalable approach for producing high-performance hydrogels and polymer networks.
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Acknowledgements
This work was financially supported by the National Key Research and Development Program of China (2024YFA1107600), the 173 Plan Project (2019-JCJQ-ZD-359-00), the National Natural Science Foundation of China (32121005 and 22475129) and the Interdisciplinary Program of Shanghai Jiao Tong University (YG2022ZD017, YG2023ZD16).
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Q.L. and L.Z. conceived the ideas. B.B., C.S., Q.Z. and T.C. were responsible for the experimental concept, design and data analysis. B.B., C.S., Q.Z., T.C., C.X. and T.L. prepared materials, performed the mechanical tests and analysed the data. B.B., C.S. and L.J. performed the structural characterization and analysed the data. J.L. and W.W. performed the simulation and analysed the data. B.B., Q.L. and J.L. wrote the manuscript. L.Z. and Q.L. provided financial support and supervised all aspects of this work. All authors commented on the manuscript and its revisions.
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Nature Synthesis thanks Andreas Walther and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Peter Seavill, in collaboration with the Nature Synthesis team.
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Supplementary Information
Supplementary Information (Synthetic materials, Methods, Algorithm description), Figs. 1–36, Tables 1–4 and Videos 1–3.
Supplementary Video 1
Fluorescence and bright-field images of a representative microgel (with NB on HA microgels) were recorded, illustrating the formation of interphase connections via the PTPC reaction. The video provides a sequential visualization of the images captured during photoirradiation, with a recording frequency of one frame per 10 s. A flash of light in the video originates from exposure to 395-nm photoirradiation. The video playback speed is accelerated eight times.
Supplementary Video 2
The video offers a sequential visualization of the images captured during the photoirradiation process, providing a broader view encompassing multiple microgels compared with Supplementary Video 1.
Supplementary Video 3
A 3D fluorescence image capturing the microstructures of the HANB-MA gel was recorded, with sample dimensions measuring 1.16 mm × 1.16 mm × 0.05 mm. The video provides a comprehensive visualization of the microstructure within the internal section of the gel.
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Bao, B., Shi, C., Zeng, Q. et al. Photocoupling of propagating radicals during polymerization realizes universal network strengthening. Nat. Synth (2025). https://doi.org/10.1038/s44160-025-00872-x
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DOI: https://doi.org/10.1038/s44160-025-00872-x
