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1. Dynamically Cross‐Linked Semicrystalline Thiol–Ene Photopolymers for Additive Manufacturing of Recyclable and Adaptive Materials

   https://doi.org/10.1002/smll.202505122  

   Alfarhan, Saleh; Chen, Mengdi; Huish, Jackson; Jin, Kailong (August 2025, Small)

   Abstract Current photopolymers are mainly produced by (meth)acrylate‐based photoresins, possessing permanently cross‐linked structures that prohibit their chemical recycling. This study reports a one‐step, scalable synthesis of dynamically cross‐linked semicrystalline thiol–ene photopolymers comprising exchangeable disulfide bonds with excellent material performance, shape memory/adaptive characteristics, and chemical recyclability. These photopolymers are synthesized via stoichiometric thiol–ene click reactions using commercial reagents, including difunctional ene, alkyl dithiol giving rise to crystallinity, thiol‐terminated oligomer comprising dynamic disulfide bonds, and trithiol cross‐linker. Cross‐link density is systematically controlled by varying trithiol cross‐linker content to tune degrees of crystallinity and mechanical properties over a wide range, e.g., Young's modulus from 4 to 138 MPa, elongation‐at‐break from 40 to 370%, and toughness from 0.3 to 32 MJ m⁻³. Importantly, these dynamically cross‐linked photopolymers undergo complete decross‐linking via thiol‐disulfide exchange reactions with small‐molecule thiols at 120 °C in a solvent‐ and catalyst‐free manner, yielding liquid thiol‐terminated oligomers. These recycled thiol‐terminated oligomers are used to synthesize next‐generation dynamically cross‐linked thiol–ene photopolymers with identical material composition and full property retention, demonstrating closed‐loop recycling. Promisingly, these new thiol–ene photoresins demonstrate excellent feasibility for Digital Light Processing (DLP)‐based 3D printing of high‐resolution objects with complex geometries, preserved crystallinity and recyclability, and unique shape memory/adaptive characteristics. 

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2. Covalent Adaptable Networks with Rapid UV Response Based on Reversible Thiol–Ene Reactions in Silicone Elastomers

   https://doi.org/10.1021/acs.macromol.3c01841  

   Huo, Miao; Hu, Jerry G.; Clarke, David R. (November 2023, Macromolecules)

   PhotoCAN silicone elastomers, based on the thiol–ene reaction, exhibit rapid and reversible changes in dynamic modulus at room temperature when illuminated by UV. By combining results from magic angle spinning solid-state NMR as well as EPR and rheometry measurements, both under UV, it is concluded that the mechanical response can be attributed to a combination of dissociative, associative, and oxidation reactions. The cleavage of the C–S bonds under UV in the presence of an excess of thiyl radicals is identified as the reversible dissociative reaction responsible for abrupt drops in the storage modulus. A slower but concurrent reaction is a termination process involving thiyl radicals to form disulfide bonds. A kinetic model is developed that successfully relates the rates of the underlying reaction mechanisms to changes in the storage modulus. The results provide a basis for designing new, ambient temperature photoresponsive covalently adaptive network materials. 

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3. A strong, reversible, and conformal adhesive gel for diverse plants

   https://doi.org/10.1126/sciadv.adz6379  

   Zhao, Jiayu; Guan, Zhecun; Luthra, Rohan; Opdensteinen, Patrick; Ho, Brandon; Li, Xiao; Park, Yong-Jin; Kwak, Min Sub; Ko, Hyunhyub; Steinmetz, Nicole F; et al (April 2026, Science Advances)

   Developing plant adhesives opens opportunities for studying and optimizing plant growth through precision pesticide and nutrient delivery, plant health monitoring, and human-plant interaction. However, diverse and changing topologies and chemical compositions of plants during growth present challenges in designing effective and universal adhesives. In this study, we address this challenge by developing a gel composite consisting of a biopolymer that enables dynamic covalent bonding with plant surfaces and cross-linked polyacrylamide, which provides adaptability. This composite gel demonstrates strong yet reversible adhesion on both hairy and nonhairy plant surfaces. Its adhesion strength exceeds that of previously reported noninvasive plant adhesives by an order of magnitude. This achievement enables localized and sustained drug delivery to plant tissues and allows for stable plant actuation via electrical stimulation, opening pathways for modulating sensitive plant systems. 

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4. Surface-Aligned Cholesteric Liquid Crystalline Elastomers with Tunable Mechanical Properties via Thiol–Ene Chemistry

   https://doi.org/10.1021/acs.macromol.5c00861  

   Phillips, Alexis T; Chen, Judy C; Kennedy, David T; White, Timothy J (June 2025, Macromolecules)

   Cholesteric liquid crystals (CLCs) exhibit Bragg reflection due to their spontaneous self-assembly into a one-dimensional photonic structure. Retaining this cholesteric order in a polymer network requires functionalizing liquid crystals with reactive end groups. However, conventional chemistries for synthesizing cholesteric liquid crystalline polymers often result in poor surface alignment and reduced optical quality. In this work, we investigate a thiol−ene step-growth polymerization approach to fabricate cholesteric liquid crystalline elastomers (CLCEs) with tunable mechanical properties and improved optical quality. By varying the cross-link density, we systematically study the effects on haze, cross-linking degree, and mechanical response. Compared to existing cholesteric liquid crystalline polymers, the thiol−ene-based CLCEs exhibit enhanced surface alignment, reduced haze, and greater mechanical tunability. These materials are further benchmarked against CLCEs synthesized via thiol−acrylate chain transfer polymerization, highlighting the advantages of the thiol−ene reaction for achieving precisely controlled properties in cholesteric polymer networks. 

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5. Fast, strong, and reversible adhesives with dynamic covalent bonds for potential use in wound dressing

   https://doi.org/10.1073/pnas.2203074119  

   Chen, Mingtao; Wu, Yue; Chen, Baohong; Tucker, Alexander M.; Jagota, Anand; Yang, Shu (July 2022, Proceedings of the National Academy of Sciences)

   Adhesives typically fall into two categories: those that have high but irreversible adhesion strength due to the formation of covalent bonds at the interface and are slow to deploy, and others that are fast to deploy and the adhesion is reversible but weak in strength due to formation of noncovalent bonds. Synergizing the advantages from both categories remains challenging but pivotal for the development of the next generation of wound dressing adhesives. Here, we report a fast and reversible adhesive consisting of dynamic boronic ester covalent bonds, formed between poly(vinyl alcohol) (PVA) and boric acid (BA) for potential use as a wound dressing adhesive. Mechanical testing shows that the adhesive film has strength in shear of 61 N/cm 2 and transcutaneous adhesive strength of 511 N/cm 2 , generated within 2 min of application. Yet the film can be effortlessly debonded when exposed to excess water. The mechanical properties of PVA/BA adhesives are tunable by varying the cross-linking density. Within seconds of activation by water, the surface boronic ester bonds in the PVA/BA film undergo fast debonding and instant softening, leading to conformal contact with the adherends and reformation of the boronic ester bonds at the interface. Meanwhile, the bulk film remains dehydrated to offer efficient load transmission, which is important to achieve strong adhesion without delamination at the interface. Whether the substrate surface is smooth (e.g., glass) or rough (e.g., hairy mouse skin), PVA/BA adhesives demonstrate superior adhesion compared to the most widely used topical skin adhesive in clinical medicine, Dermabond. 

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