Light-Mediated Synthesis and Reprocessing of Dynamic Bottlebrush Elastomers under Ambient Conditions

Revealing Transition State Stabilization in Organocatalytic Ring-Opening Polymerization Using Data Science

In nature, enzymes leverage constituent amino acid residues to create catalytically active sites to effect high reactivity and selectivity. Multicomponent host-guest assemblies have been exploited to mimic enzymatic microenvironments by pre-organizing a network of noncovalent interactions. While organocatalysts such as thioureas have gained widespread success in organic transformation and controlled polymerization, evaluation of the participating structural features in the transition state (TS) remains challenging. Herein, we report the use of data science tools, i.e., a decision-tree-based machine-learning algorithm and Shapley additive explanations (SHAP) analysis, to model reactivity and regioselectivity in a thiourea-catalyzed ring-opening polymerization of 1,2-dithiolanes. Variation of aryl substituent position and electronic characteristics reveals key catalyst features involved in the TS. The analysis of feature importance helps explain the reason behind the optimal performance of (pseudo)halogen-substituted catalysts. Furthermore, the structural basis for the unveiled reactivity-regioselectivity trade-off in the catalysis are established.

Responsive, Structure-Shifting Bottlebrush Copolymer Particles

Structure-shifting polymer particles are of great interest for developing smart soft materials. Here, nanostructured polymer particles capable of switching their morphology in response to external stimuli are presented. The key design is to use a bottlebrush random copolymer with a polydisulfide backbone as a self-assembly building block, in which the polymerization/depolymerization of the dynamic backbone can drive the transformation of the inner particle structure. Nanostructured colloids are generated upon confined assembly of the bottlebrush copolymers in the emulsion droplet, in contrast to the formation of compartmentalized colloids from a blend of polystyrene (PS) and poly(dimethylsiloxane) (PDMS) macromonomers. Exploring the morphology-switching capability reveals that depolymerization of the bottlebrush backbone transforms nanostructured colloids into compartmentalized particles, with intermediate morphologies observed during the depolymerization. Additionally, the morphological transformation is general across multiple inner nanostructures including concentric lamellae, coiled cylinders, and spheres. Importantly, reversible morphology switching capability is realized through polymerization-depolymerization-repolymerization cycles. Finally, the functional potential of these structure-shifting particles is demonstrated by incorporating aggregation-induced emission luminogens (AIEgen). The particles exhibit significant difference in the photoluminescence intensity as a function of particle morphology, attributed to differences in the size of the polymeric domains and the corresponding aggregated state of the luminogens.

Lanthanide Coordinated Poly(Thioctic Acid) Materials with Enhanced Strength and Room Temperature Self-Healing Performance

Poly(thioctic acid) materials exhibit excellent room-temperature self-healing properties due to their dynamic disulfide-bonded supramolecular network and have been widely used in applications such as wearable devices, adhesives, and wound patches. However, the limited mechanical properties of poly(thioctic acid) materials with dynamic supramolecular networks limit their practical applications. Therefore, there is an urgent need for a low-energy-consuming and facile method to enhance their mechanical strength and maintain their room-temperature self-healing properties. Here, a novel approach is developed by introducing Eu3⁺-coordination into the copolymerization of thioctic acid (TA) and sodium thioctate (ST), forming hierarchical dynamic supramolecular networks. Copolymerization of TA and ST under mild conditions (60 °C in ethanol/water solvent) introduces stable hydrogen-bonding interactions without additional chemical cross-linkers. Further Eu3⁺-coordination increases the mechanical modulus of the films by more than 100-fold while significantly improving toughness and strength. This is attributed to the large ionic radius and high coordination number of Eu ions with carboxylates which significantly enhanced the strength of the crosslinked network. This strategy offers a novel pathway for developing supramolecular materials with an optimal balance of mechanical strength and self-repairing capabilities, advancing their potential in various applications.

A lignin-based multifunctional elastomer via facile fabrication for wearable strain sensors

Elastomer-based electronics have the potential to maintain both electrochemical conductivity and mechanical properties simultaneously, paving the way for the development of stretchable sensors. However, creating sensors that are extremely stretchable, wearable, and highly sensitive remains a significant challenge. In this work, we present a novel fully bio-based multifunctional polymer (FPL/PTA) designed using thioctic acid (TA) and formaldehyde-protected lignin (FPL). The FPL serves as both a cross-linking agent and a free radical quenching agent. The FPL/PTA features an adaptive polymer network cross-linked by dynamic covalent disulfide bonds and enhanced by multiple non-covalent interactions. This unique structure imparts the material with stretchability, self-healing properties, hydrophobicity, swelling resistance, self-adhesion, and fully recyclable, degradable characteristics. In addition, the simple preparation route, multiple functions, and green characteristics give the elastomer and choline chloride combination as a strain sensor. The sensor exhibits exceptional sensitivity to strain, repeatability, and durability, enabling it to monitor a wide range of human movements, including joint articulation, speech, and swallowing. We believe that the overall performance and feasibility of manufacturing the developed FPL/PTA marks it as a promising multifunctional strain sensor for applications in flexible wearable electronic devices and humanoid robots.

Strategies to Improve the Sustainability of Silicone Polymers

Silicones underpin an enormous range of simple and advanced technologies. Often, only small quantities of silicone are used to enable a technology such that, on a "per use" basis, one might suppose the environmental impact is low. However, silicone preparation processes have a very high carbon footprint, and billions of kg are produced each year. To provide context to the consideration of new strategies to improve silicone sustainability, we first outline traditional silicone chemistry and then describe strategies to improve the degree to which silicones are green, sustainable and circular. One strategy involves dilution of the silicone oil or elastomer by tethering organic entities, particularly natural products, that may provide new properties including facilitated degradation in nature at end-of-life. A greater focus is given to strategies that permit extensive reuse and repurposing of oils and elastomers (e.g., with thermoplastic elastomers), before the silicone undergoes recycling. Each reuse, repurposing or recycling step reduces the net carbon footprint. These mostly involve straightforward, high-yielding organic chemical processes that work efficiently in a silicone milieu. Silicones will eventually end up in the environment, where linear oils are known to rapidly degrade, particularly when compared to organic polymers. Alternative strategies that permit triggered or biological degradation of oils and, more importantly elastomers, are described, including enzymatic degradation and composting.

Circular 3D printing of high-performance photopolymers through dissociative network design

One approach for closed-loop plastics recycling relies on reverting polymers back into monomers because one can then make new plastics without loss of properties. This depolymerization requirement restricts the molecular design to making polymers with high mechanical performance. We report a three-dimensional (3D) printing chemistry through stepwise photopolymerization by forming dithioacetal bonds. The polymerized network can be transformed back into a photoreactive oligomer by dissociation of the dithioacetal bonds. This network-oligomer transformation is reversible, therefore allowing circular 3D printing using the same material. Our approach offers the flexibility of making modular adjustments in the design of the network backbone of a polymer. This allows access to fully recyclable elastomers, crystalline polymers, and rigid glassy polymers with high mechanical toughness, making them potentially suitable for diverse applications.

Photo-Patternable and Healable Polymer Semiconductor Enabled by Dynamic Covalent Disulfide Bonding

Apart from charge transport property, polymer semiconductors with patternable and healable functions are highly demanding for the fabrication of organic circuits. Herein, by leveraging the dynamic covalent disulfide bonding of thioctic acid (TA) groups, we successfully integrate photo-patterning and thermal-healing capabilities into a single diketopyrrolopyrrole (DPP)-based polymer semiconductor for the first time. The results show that the thin film of DPP-based conjugated donor-acceptor polymer with TA groups in the side chains exhibits excellent photo-patterning capability under 365 nm UV light irradiation, with sensitivity (S) of 210 mJ⋅cm-2 and contrast (γ) of 1.2. Importantly, the patterning process has minimal impact on thin film morphology, interchain stacking, and charge transport mobility. Moreover, the patterned thin films, which were initially scratched, can be well healed after exposure to chloroform vapor and further thermal annealing, and simultaneously the charge mobility can be restored. In comparison, the scratched thin film of PDPP4T without TA groups in the side chains achieves only 82.6 % recovery of scratch depth and 54.5 % recovery of charge mobility under the same conditions. These results demonstrate the feasibility of constructing multifunctional polymer semiconductors by incorporating TA groups in the side chains, offering a new pathway to lithography-compatible, self-healing smart flexible devices.

UV-Responsive Adhesive Based on Polystyrene-block-Poly(Ethyl Lipoate) Copolymer

Block copolymers (BCPs), capable of self-assembling into various nanoscale structures, are widely used in adhesives owing to their versatile properties. However, conventional BCP-based adhesives pose environmental concerns: they are petroleum-derived, non-degradable, and have a non-tunable adhesion strength. To address these challenges, a novel BCP is designed comprising a conventional hard segment, polystyrene (PS), and a green rubbery segment, poly(ethyl lipoate) (PEtLp), derived from the bio-based molecule α-lipoic acid. The PS-b-PEtLp is synthesized via the base-catalyzed ring-opening polymerization from thiol-terminated PS. Adhesion tests showed that PS-b-PEtLp with cylindrical nanostructures exhibited higher adhesion strength than that with lamellar structures. Importantly, the dynamic disulfide bonds in PEtLp enable a reversible and adjustable adhesion strength under UV light. Upon UV irradiation, the adhesion strength decreases by approximately half, facilitating easy separation from the adherends. Additionally, the selective depolymerization of the PEtLp block achieves 100% conversion, enabling the recovery of the monomer (EtLp) and macroinitiator (thiol-terminated PS). This study introduces a sustainable, degradable, and reusable adhesive derived from renewable resources, providing a promising solution to the environmental challenges associated with traditional petroleum-based adhesives.

Photo-regulated disulfide crosslinking: a versatile approach to construct mucus-inspired hydrogels

The remarkable defensive ability of native mucus against pathogens has encouraged scientists to map its structure--property correlation and its influence on immune defense mechanisms. However, its poorly defined structure, source-dependent composition, and low availability limit the usefulness of native mucus in the laboratory. This gap creates a strong demand for the development of synthetic mucus-mimetic materials. Here, we report a straightforward strategy for constructing mucus-mimetic hydrogels through photo-regulated disulfide crosslinking. Light-responsive 1,2-dithiolane attached to a linear polyglycerol sulfate (lPGS) backbone allows the macromolecular building blocks to crosslink and form the hydrogel, which mirrors the chemistry of native mucus hydrogel formation with its disulfide-linked mucin chains. The viscoelastic properties of the hydrogel can be easily tuned by controlling both the light exposure time and the number of 1,2-dithiolane units within the polymer backbone. Furthermore, localized UV irradiation allows for spatially resolved hydrogel formation. Importantly, this synthetic polymer can directly crosslink with native mucin, bovine submaxillary mucin (BSM), to convert it into a hydrogel at physiological pH. The versatility of this approach - hydrogel formation via photo-regulated disulfide crosslinking - can be used to develop a synthetic mucus model.

Exploiting Photohalide Generation in Shape and Multichromatic Color Patterning of Polymer-Perovskite Nanocomposites

The ability to arrange brightly fluorescent nanoscale materials into well-defined patterns is critically important in advanced optoelectronic structures. Traditional methods for doing so generally involve depositing different color quantum dot "inks," irradiating reactive (e.g., cross-linkable) ligands at their surface, and then lifting off the unexposed sections in a developer solvent. Here, we outline a fundamentally different approach for directly patterning the emission color of nanocomposite thin films utilizing mask-based lithographic techniques and laser scanning methods. In this system, a polymer film containing cesium lead halide nanocrystals (NCs) is embedded with an organohalide─termed a "photohalide generator"─which undergoes a light-triggered, perovskite-catalyzed reduction and release of halide anion for uptake by the NC lattice, markedly shifting its band gap. In this manner, a blue emitting (CsPbBr1.5Cl1.5) film becomes green and/or red in the exposed areas of a photomask, replicating the mask features as a multichromatic array (e.g., green, red, etc. colors against a blue background). The resolution limits of this materials system were probed using laser scanning tools capable of writing intricate patterns with feature sizes approaching a single micron─more than an order of magnitude smaller than the most comparable methods based on inkjet printing. Lastly, these methods are extended to a combined shape and color patterning process for making free-standing filamentous structures with striped and alternating fluorescence emission along their length.

Synthesis of Cationic Cyclic Oligo(disulfide)s via Cyclo-Depolymerization: A Redox-Responsive and Potent Antibacterial Reagent

Antimicrobial peptides (AMPs) and synthetic topologically defined peptide mimics have been developed as alternatives to traditional small-molecule antibiotics. AMP mimetics arising from linear polymers used widely in preclinical studies have shown promise but have limited stability. Oligomers possessing cyclic topology have been proposed to have increased stability but remain understudied due to synthetic challenges and concerns over cytotoxicity. Herein, we present an efficient approach to prepare cationic, cyclic oligo(disulfide)s (CCOs) from lipoic acid derivatives. The CCOs are obtained in a one-pot cascade reaction of ring-opening polymerization preceding an in situ cyclo-depolymerization. CCOs are effective against a broad spectrum of bacteria, exhibiting a 5.43-log reduction in 5 min against Escherichia coli. They did not induce antimicrobial resistance during 24 successive passages in vitro. The cytotoxicity of CCOs is reduced by exploiting glutathione-triggered degradation. Further, fine-tuning of the cationic-to-hydrophilic ratio in CCOs has yielded improved stability in serum and a high selective index (HC50/MIC > 1280) against methicillin-resistant Staphylococcus aureus. In an infected wound rodent model, CCOs have shown substantial antibacterial potency against S. aureus, underscoring their therapeutic potential as a new class of antimicrobial agents.

Reprocessable and Recyclable Materials for 3D Printing via Reversible Thia-Michael Reactions

The development of chemically recyclable polymers for sustainable 3D printing is crucial to reducing plastic waste and advancing towards a circular polymer economy. Here, we introduce a new class of polythioenones (PCTE) synthesized via Michael addition-elimination ring-opening polymerization (MAEROP) of cyclic thioenone (CTE) monomers. The designed monomers are straightforward to synthesize, scalable and highly modular, and the resulting polymers display mechanical performance superior to commodity polyolefins such as polyethylene and polypropylene. The material was successfully employed in 3D printing using fused-filament fabrication (FFF), showcasing excellent printability and mechanical recyclability. Notably, PCTE-Ph retains its tensile strength and thermal stability after multiple mechanical recycling cycles. Furthermore, PCTE-Ph can be depolymerized back to its original monomer with a 90 % yield, allowing for repolymerization and establishing a successful closed-loop life cycle, making it a sustainable alternative for additive manufacturing applications.

ROMP of Macromonomers Prepared by ROMP: Expanding Access to Complex, Functional Bottlebrush Polymers

Graft-through ring-opening metathesis polymerization (ROMP) of norbornene-terminated macromonomers (MMs) prepared using various polymerization methods has been extensively used for the synthesis of bottlebrush (co)polymers, yet the potential of ROMP for the synthesis of MMs that can subsequently be polymerized by graft-through ROMP to produce new bottlebrush compositions remains untapped. Here, we report an efficient "ROMP-of-ROMP" method that involves the synthesis of norbornene-terminated poly(norbornene imide) (PNI)-based MMs that, following ROMP, provide new families of bottlebrush (co)polymers and "brush-on-brush" hierarchical architectures. In the bulk state, the organization of the PNI pendants drives bottlebrush backbone extension to enable rapid assembly of asymmetric lamellar morphologies with large asymmetry factors. Overall, this work expands the scope of complex macromolecular architectures and provides insights into the interplay of backbone rigidity and self-assembly that will guide future nanolithography applications.

Radical Ring-Opening Polymerization: Unlocking the Potential of Vinyl Polymers for Drug Delivery, Tissue Engineering, and More

Synthetic vinyl polymers have long been recognized for their potential to be utilized in drug delivery, tissue engineering, and other biomedical applications. The synthetic control that chemists have over their structure and properties is unmatched, allowing vinyl polymer-based materials to be precisely engineered for a range of therapeutic applications. Yet, their lack of biodegradability compromises the biocompatibility of vinyl polymers and has held back their translation into clinically used treatments for disease thus far. In recent years, radical ring-opening polymerization (rROP) has emerged as a promising strategy to render synthetic vinyl polymers biodegradable and bioresorbable. While rROP has long been touted as a strategy for preparing biodegradable vinyl polymers for biomedical applications, the translation of rROP into clinically approved treatments for disease has not yet been realized. This review highlights the opportunities for leveraging rROP to render vinyl polymers biodegradable and unlock their potential for use in biomedical applications.

Enhancing the Biomimetic Mechanics of Bottlebrush Graft-Copolymers through Selective Solvent Annealing

Self-assembled networks of bottlebrush copolymers are promising materials for biomedical applications due to a unique combination of ultra-softness and strain-adaptive stiffening, characteristic of soft biological tissues. Transitioning from ABA linear-brush-linear triblock copolymers to A-g-B bottlebrush graft copolymer architectures allows significant increasing the mechanical strength of thermoplastic elastomers. Using real-time synchrotron small-angle X-ray scattering, it is shown that annealing of A-g-B elastomers in a selective solvent for the linear A blocks allows for substantial network reconfiguration, resulting in an increase of both the A domain size and the distance between the domains. The corresponding increases in the aggregation number and extension of bottlebrush strands lead to a significant increase of the strain-stiffening parameter up to 0.7, approaching values characteristic of the brain and skin tissues. Network reconfiguration without disassembly is an efficient approach to adjusting the mechanical performance of tissue-mimetic materials to meet the needs of diverse biomedical applications.

Versatile Light-Mediated Synthesis of Degradable Bottlebrush Polymers Using α-Lipoic Acid

Bottlebrush polymers have a variety of useful properties including a high entanglement molecular weight, low Young's modulus, and rapid kinetics for self-assembly. However, the translation of bottlebrushes to real-world applications is limited by complex, multi-step synthetic pathways and polymerization reactions that rely on air-sensitive catalysts. Additionally, most bottlebrushes are non-degradable. Herein, we report an inexpensive, versatile, and simple approach to synthesize degradable bottlebrush polymers under mild reaction conditions. Our approach relies on the "grafting-through" polymerization of α-lipoic acid (LA)-functionalized macromonomers. These macromonomers can be polymerized under mild, catalyst-free conditions, and due to reversibility of the disulfide bond in LA, the resulting bottlebrush polymers can be depolymerized by cleaving disulfide backbone bonds. Bottlebrushes with various side-chain chemistries can be prepared through the atom transfer radical polymerization (ATRP) of LA-functionalized macromonomers, and the backbone length is governed by the macromonomer molecular weight and solvent polarity. We also demonstrate that LA-functionalized macromonomers can be copolymerized with acrylates to form degradable bottlebrush networks. This work demonstrates the preparation of degradable bottlebrush polymers with a variety of side-chain chemistries and provides insight into the light-mediated grafting-through polymerization of dithiolane-functionalized macromonomers.

Exploring α-Lipoic Acid Based Thermoplastic Silicone Adhesive: Towards Sustainable and Green Recycling

Considering the demand for the construction of a sustainable future, it is essential to endow the conventional thermoset silicone adhesive with reuse capability and recyclability. Although various research attempts have been made by incorporating reversible linkages, developing sustainable silicone adhesives by natural linkers is still challenging, as the interface between the natural linker and the silicone is historically difficult. We exploited the possibility of utilizing α-lipoic acid, a natural linker, to construct a sustainable silicone adhesive. Via the simultaneous ring-opening reaction between the COOH and epoxide-functionalized silicone and the polymerization of the α-lipoic acid, the resulting network exhibited dynamic properties. The shear strength of the LASA90 presented strong adhesion (up to 88 kPa) on various substrates including steel, aluminum, PET, and PTFE. Meanwhile, reversible adhesion was shown multiple times under mild heating conditions (80 °C). The rheology, TG-DTA, DSC, and 1H NMR showed that the degradation of the LASA occurred at 150 °C via the retro-ROP of the five-membered disulfide ring, indicating their recyclability after usage. Conclusively, we envision that a silicone adhesive based on α-lipoic acid as a natural linker is more sustainable than conventional silicone thermosets because of its desired properties, strong adhesion, reversibility, and on-demand heat degradation.

Sustainable and Recyclable Acrylate Resins for Liquid-Crystal Display 3D Printing Based on Lipoic Acid

The development of renewable vinyl-based photopolymer resins offers a promising solution to reducing the environmental impact associated with 3D printed materials. This study introduces a bifunctional lipoate cross-linker containing a dynamic disulfide bond, which is combined with acrylic monomers (n-butyl acrylate) and conventional photoinitiators to develop photopolymer resins that are compatible with commercial stereolithography 3D printing. The incorporation of disulfide bonds within the polymer network's backbone imparts the 3D printed objects with self-healing capabilities and complete degradability. Remarkably, the degraded resin can be fully recycled and reused for high-resolution reprinting of complex structures while preserving mechanical properties that are comparable to the original material. This proof-of-concept study not only presents a sustainable strategy for advancing acrylate-based 3D printing materials, but also introduces a novel approach for fabricating fully recyclable 3D-printed structures. This method paves the way for reducing the environmental impact while enhancing material reusability, offering significant potential for the development of eco-friendly additive manufacturing.

Biomass and Transparent Supramolecular Elastomers for Green Electronics Enabled by the Controlled Growth and Self-Assembly of Dynamic Polymer Networks

Determining the optimal method for preparing supramolecular materials remains a profound challenge. This process requires a combination of renewable raw materials to create supramolecular materials with multiple functions and properties, including simple fabrication, sustainability, a dynamic nature, good toughness, and transparency. In this work, a strategy is presented for toughening supramolecular networks based on solid-phase chain extension. This toughening strategy is simple and environmentally friendly. In addition, a series of biobased elastomers are designed and prepared with adjustable performance characteristics. This strategy can significantly improve the transparency, tensile strength, and toughness of the synthesized elastomer. The synthesized biobased elastomers have great ductility, repairability, and recyclability, and they show good adhesion and dielectric properties. A biobased ionic skin is assembled from these biobased elastomers. Assembled ionic skin can sensitively detect external stimuli (such as stretching, bending, compression, or temperature changes) and monitor human movement. The conductive and dielectric layers of the biobased ionic skin are both obtained from renewable raw materials. This research provides novel molecular design approaches and material selection methods for promoting the development of green electronic devices and biobased elastomers.

Principles for designing sustainable and high-strain rate stress wave dissipating materials

Dynamic covalent networks serve as effective tools for dissipating high-strain rate mechanical energy throughout reversible bond exchange reactions. Despite their potential, a gap exists in understanding how polymer chain mobility and the kinetics of bond exchange reactions impact the energy dissipating capabilities of dynamic covalent networks. This study presents an optimal strategy to enhance energy dissipation by controlling the side chain structures and bond exchange rates of dynamic covalent networks. Lipoic acid-derived polymers are chosen as our model system due to their easily tunable side chains and disulfide-rich backbones. High-strain rate stress waves are subjected to the polymers using a laser-induced shock wave technique. A strong correlation is observed between the energy dissipation capability and the glass transition temperature of the poly(disulfide)s. Furthermore, the addition of a catalyst to accelerate the disulfide exchange reaction improves energy dissipation. Leveraging the inherent nature of cyclic disulfides, our polymers exhibit self-healing and chemical recycling to monomers. The principles observed in this study provide a rational framework for designing sustainable and efficient energy dissipating materials.

Reprocessible, Reusable, and Self-Healing Polymeric Adsorbent for Removing Perfluorinated Pollutants

Here, we report a reprocessible, reusable, self-healing, and form-switching polymeric adsorbent for remediating fluorinated pollutants in water. The copolymer hydrogel is designed to contain fluorophilic segments and cationic segments to induce strong binding with perfluorinated pollutants. The sorption performance reveals rapid and quantitative removal of these pollutants, driven by the synergistic effect of fluorophilic and electrostatic interaction. Importantly, a disulfide-containing dynamic crosslinker plays a crucial role in imparting multifunctionality. This enables self-healing by the restoration of crosslinks at the cut surfaces by disulfide exchange reactions and allows for the repeated use of the adsorbent via multiple adsorption-desorption cycles. Furthermore, the adsorbent is reprocessible by cleaving the crosslinks to afford linear copolymers, which can be repolymerized into a hydrogel network on demand. Also, form-switching capability is showcased through the aqueous self-assembly of linear copolymers into a fluorinated micelle, serving as another form of adsorbent for pollutant removal.

Photoinduced Dithiolane Crosslinking for Multiresponsive Dynamic Hydrogels

While many hydrogels are elastic networks crosslinked by covalent bonds, viscoelastic hydrogels with adaptable crosslinks are increasingly being developed to better recapitulate time and position-dependent processes found in many tissues. In this work, 1,2-dithiolanes are presented as dynamic covalent photocrosslinkers of hydrogels, resulting in disulfide bonds throughout the hydrogel that respond to multiple stimuli. Using lipoic acid as a model dithiolane, disulfide crosslinks are formed under physiological conditions, enabling cell encapsulation via an initiator-free light-induced dithiolane ring-opening photopolymerization. The resulting hydrogels allow for multiple photoinduced dynamic responses including stress relaxation, stiffening, softening, and network functionalization using a single chemistry, which can be supplemented by permanent reaction with alkenes to further control network properties and connectivity using irreversible thioether crosslinks. Moreover, complementary photochemical approaches are used to achieve rapid and complete sample degradation via radical scission and post-gelation network stiffening when irradiated in the presence of reactive gel precursor. The results herein demonstrate the versatility of this material chemistry to study and direct 2D and 3D cell-material interactions. This work highlights dithiolane-based hydrogel photocrosslinking as a robust method for generating adaptable hydrogels with a range of biologically relevant mechanical and chemical properties that are varied on demand.

UV-Mediated Facile Fabrication of a Robust, Fully Renewable and Controllably Biodegradable Poly(lactic acid)-Based Covalent Adaptable Network

A robust and fully biobased covalent adaptable network (CAN) that allows recyclability, biocompatibility, and controlled biodegradability is reported. The CAN was fabricated through a simple photo-cross-linking method, wherein low-molecular-weight poly(lactic acid) (∼3 kDa) was modified with end 1,2-dithiolane rings through a one-step Steglich esterification reaction with thioctic acid (TA). These incorporated 1,2-dithiolane rings undergo photoinduced ring-opening polymerization, thus enabling the cross-linking of poly(lactic acid) with abundant dynamic disulfide bonds. The resultant CAN demonstrates excellent transparency, effective UV-blocking capabilities below 320 nm, robust tensile strength (∼39 MPa), and superior dimensional stability at 80 °C, alongside attractive biocompatibility. Moreover, owing to the dynamic exchange and redox-responsiveness of disulfide bonds, the material can be recycled by hot-pressing and a reduction-oxidation process while also being capable of controllably biodegrading at the end of its lifecycle. Furthermore, it exhibits reconfigurable shape memory properties with fast recovery. This study elucidates a straightforward approach to fabricating multifunctional and sustainable polymer materials with potential applications in diverse fields such as packaging, coating, and biomedicine.

Esterase-Responsive Floxuridine-Tethered Multifunctional Nanoparticles for Targeted Cancer Therapy

Floxuridine is a potential clinical anticancer drug for the treatment of various cancers. However, floxuridine typically causes unfavorable side effects due to its very poor tumor selectivity, and, hence, there is a high demand for the development of novel approaches that permit the targeted delivery of floxuridine into cancerous cells. Herein, the design and synthesis of an esterase-responsive multifunctional nanoformulation for the targeted delivery of floxuridine in esterase-overexpressed cancer cells is reported. Photopolymerization of floxuridine-tethered lipoic acid results in the formation of amphiphilic floxuridine-tethered poly(disulfide). Self-assembly of the amphiphilic polymer results in the formation of nanoparticles with floxuridine decorated on the surfaces of the particles. Integration of aptamer DNA for nucleolin onto the surface of the nanoparticle is demonstrated by exploring the base-pairing interaction of floxuridine with adenine. Targeted internalization of the aptamer-decorated nanoparticle into nucleolin-expressed cancer cells is demonstrated. Esterase triggered cleavage of the ester bond connecting floxuridine with the polymer backbone, and the subsequent targeted delivery of floxuridine into cancer cells is also shown. Excellent therapeutic efficacy is observed both in vitro and also in the 3D tumor spheroid model. This noncovalent strategy provides a simple yet effective strategy for the targeted delivery of floxuridine into cancer cells in a less laborious fashion.

Wearable and Recyclable Water-Toleration Sensor Derived from Lipoic Acid

Flexible wearable sensors recently have made significant progress in human motion detection and health monitoring. However, most sensors still face challenges in terms of single detection targets, single application environments, and non-recyclability. Lipoic acid (LA) shows a great application prospect in soft materials due to its unique properties. Herein, ionic conducting elastomers (ICEs) based on polymerizable deep eutectic solvents consisting of LA and choline chloride are prepared. In addition to the good mechanical strength, high transparency, ionic conductivity, and self-healing efficiency, the ICEs exhibit swelling-strengthening behavior and enhanced adhesion strength in underwater environments due to the moisture-induced association of poly(LA) hydrophobic chains, thus making it possible for underwater sensing applications, such as underwater communication. As a strain sensor, it exhibits highly sensitive strain response with repeatability and durability, enabling the monitoring of both large and fine human motions, including joint movements, facial expressions, and pulse waves. Furthermore, due to the enhancement of ion mobility at higher temperatures, it also possesses excellent temperature-sensing performance. Notably, the ICEs can be fully recycled and reused as a new strain/temperature sensor through heating. This study provides a novel strategy for enhancing the mechanical strength of poly(LA) and the fabrication of multifunctional sensors.

Bottlebrush Networks: A Primer for Advanced Architectures

Bottlebrush networks (BBNs) are an exciting new class of materials with interesting physical properties derived from their unique architecture. While great strides have been made in our fundamental understanding of bottlebrush polymers and networks, an interdisciplinary approach is necessary for the field to accelerate advancements. This review aims to act as a primer to BBN chemistry and physics for both new and current members of the community. In addition to providing an overview of contemporary BBN synthetic methods, we developed a workflow and desktop application (LengthScale), enabling bottlebrush physics to be more approachable. We conclude by addressing several topical issues and asking a series of pointed questions to stimulate conversation within the community.

A renewably sourced, circular photopolymer resin for additive manufacturing

The additive manufacturing of photopolymer resins by means of vat photopolymerization enables the rapid fabrication of bespoke 3D-printed parts. Advances in methodology have continually improved resolution and manufacturing speed, yet both the process design and resin technology have remained largely consistent since its inception in the 1980s1. Liquid resin formulations, which are composed of reactive monomers and/or oligomers containing (meth)acrylates and epoxides, rapidly photopolymerize to create crosslinked polymer networks on exposure to a light stimulus in the presence of a photoinitiator2. These resin components are mostly obtained from petroleum feedstocks, although recent progress has been made through the derivatization of renewable biomass3-6 and the introduction of hydrolytically degradable bonds7-9. However, the resulting materials are still akin to conventional crosslinked rubbers and thermosets, thus limiting the recyclability of printed parts. At present, no existing photopolymer resin can be depolymerized and directly re-used in a circular, closed-loop pathway. Here we describe a photopolymer resin platform derived entirely from renewable lipoates that can be 3D-printed into high-resolution parts, efficiently deconstructed and subsequently reprinted in a circular manner. Previous inefficiencies with methods using internal dynamic covalent bonds10-17 to recycle and reprint 3D-printed photopolymers are resolved by exchanging conventional (meth)acrylates for dynamic cyclic disulfide species in lipoates. The lipoate resin platform is highly modular, whereby the composition and network architecture can be tuned to access printed materials with varied thermal and mechanical properties that are comparable to several commercial acrylic resins.

Towards high performance and durable soft tactile actuators

Soft actuators are gaining significant attention due to their ability to provide realistic tactile sensations in various applications. However, their soft nature makes them vulnerable to damage from external factors, limiting actuation stability and device lifespan. The susceptibility to damage becomes higher with these actuators often in direct contact with their surroundings to generate tactile feedback. Upon onset of damage, the stability or repeatability of the device will be undermined. Eventually, when complete failure occurs, these actuators are disposed of, accumulating waste and driving the consumption of natural resources. This emphasizes the need to enhance the durability of soft tactile actuators for continued operation. This review presents the principles of tactile feedback of actuators, followed by a discussion of the mechanisms, advancements, and challenges faced by soft tactile actuators to realize high actuation performance, categorized by their driving stimuli. Diverse approaches to achieve durability are evaluated, including self-healing, damage resistance, self-cleaning, and temperature stability for soft actuators. In these sections, current challenges and potential material designs are identified, paving the way for developing durable soft tactile actuators.

Dynamic Antimicrobial Poly(disulfide) Coatings Exfoliate Biofilms On Demand Via Triggered Depolymerization

Bacterial biofilms are notoriously problematic in applications ranging from biomedical implants to ship hulls. Cationic, amphiphilic antibacterial surface coatings delay the onset of biofilm formation by killing microbes on contact, but they lose effectiveness over time due to non-specific binding of biomass and biofilm formation. Harsh treatment methods are required to forcibly expel the biomass and regenerate a clean surface. Here, a simple, dynamically reversible method of polymer surface coating that enables both chemical killing on contact, and on-demand mechanical delamination of surface-bound biofilms, by triggered depolymerization of the underlying antimicrobial coating layer, is developed. Antimicrobial polymer derivatives based on α-lipoic acid (LA) undergo dynamic and reversible polymerization into polydisulfides functionalized with biocidal quaternary ammonium salt groups. These coatings kill >99.9% of Staphylococcus aureus cells, repeatedly for 15 cycles without loss of activity, for moderate microbial challenges (≈105 colony-forming units (CFU) mL-1, 1 h), but they ultimately foul under intense challenges (≈107 CFU mL-1, 5 days). The attached biofilms are then exfoliated from the polymer surface by UV-triggered degradation in an aqueous solution at neutral pH. This work provides a simple strategy for antimicrobial coatings that can kill bacteria on contact for extended timescales, followed by triggered biofilm removal under mild conditions.

Self-Powered and Self-Healable Extraocular-Muscle-Like Actuator Based on Dielectric Elastomer Actuator and Triboelectric Nanogenerator

Although dielectric elastomer actuators (DEAs) are promising artificial muscles for use as visual prostheses in patients with oculomotor nerve palsy (ONP), high driving voltage coupled with vulnerable compliant electrodes limits their safe long-term service. Herein, a self-healable polydimethylsiloxane compliant electrode based on reversible imine bonds and hydrogen bonds is prepared and coated on an acrylic ester film to develop a self-healable DEA (SDEA), followed by actuation with a high-output triboelectric nanogenerator (TENG) to construct a self-powered DEA (TENG-SDEA). Under 135.9 kV mm-1 , the SDEA exhibits an elevated actuated strain of 50.6%, comparable to the actuation under DC power. Moreover, the mechanically damaged TENG-SDEA displays a self-healing efficiency of over 90% for 10 cycles. The TENG ensures the safe using of TENG-SDEAs and an extraocular-muscle-like actuator with oriented motion ability integrated by several TENG-SDEAs is constructed. Additionally, the SDEA is directly used as a flexible capacitive sensor for real-time monitoring of the patient's muscle movement. Accordingly, a medical aid system based on a conjunction of the extraocular-muscle-like actuator and a flexible capacitive sensor is manufactured to help the patients suffering from ONP with physical rehabilitation and treatment.

Solvent-Triggered Chemical Recycling of Ion-Conductive and Self-Healable Polyurethane Covalent Adaptive Networks

Given the substantial environmental challenge posed by global plastic waste, recycling technology for thermosetting polymers has become a huge research topic in the polymer industry. Covalent adaptive networks (CANs), which can reversibly dissociate and reconstruct their network structure, represent a key technology for the self-healing, reprocessing, and recycling of thermosetting polymers. In the present study, we introduce a new series of polyurethane CANs whose network structure can dissociate via the self-catalyzed formation of dithiolane from the CANs' polydisulfide linkages when the CANs are treated in N,N-dimethylformamide (DMF) or dimethyl sulfoxide at 60 °C for 1 h. More interestingly, we found that this network dissociation even occurs in tetrahydrofuran-DMF solvent mixtures with low DMF concentrations. This feature enables a reduction in the use of high-boiling, toxic polar aprotic solvents. The dissociated network structure of the CANs was reconstructed under UV light at 365 nm with a high yield via ring-opening polydisulfide linkage formation from dithiolane pendant groups. These CAN films, which were prepared by a sequential organic synthesis and polymerization process, exhibited high thermal stability and good mechanical properties, recyclability, and self-healing performance. When lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt was added to the CAN films, the films exhibited a maximum ion conductivity of 7.48 × 10-4 S cm-1 because of the contribution of the high concentration of the pendant ethylene carbonate group in the CANs. The ion-conducting CAN films also showed excellent recyclability and a self-healing performance.

Controlled and Regioselective Ring-Opening Polymerization for Poly(disulfide)s by Anion-Binding Catalysis

Poly(disulfide)s are an emerging class of sulfur-containing polymers with applications in medicine, energy, and functional materials. However, the constituent dynamic covalent S-S bond is highly reactive in the presence of the sulfide (RS-) anion, imposing a persistent challenge to control the polymerization. Here, we report an anion-binding approach to arrest the high reactivity of the RS- chain end to control the synthesis of linear poly(disulfide)s, realizing a rapid, living ring-opening polymerization of 1,2-dithiolanes with narrow dispersity and high regioselectivity (Mw/Mn ∼ 1.1, Ps ∼ 0.85). Mechanistic studies support the formation of a thiourea-base-sulfide ternary complex as the catalytically active species during the chain propagation. Theoretical analyses reveal a synergistic catalytic model where the catalyst preorganizes the protonated base and anionic chain end to establish spatial confinement over the bound monomer, effecting the observed regioselectivity. The catalytic system is amenable to monomers with various functional groups, and semicrystalline polymers are also obtained from lipoic acid derivatives by enhancing the regioselectivity.

Lipoic acid-based vitrimer-like elastomer

Dynamic covalent networks (DCNs) are materials that feature reversible bond formation and breaking, allowing for self-healing and recyclability. To speed up the bond exchange, significant amounts of catalyst are used, which creates safety concerns. To tackle this issue, we report the synthesis of a lipoic acid-based vitrimer-like elastomer (LAVE) by combining (i) ring-opening polymerization (ROP) of lactones, (ii) lipoic acid modification of polylactones, and (iii) UV crosslinking. The melting temperature (Tm) of LAVE is below room temperature, which ensures the elastic properties of LAVE at service temperature. By carefully altering the network, it is possible to tune the Tm, as well as the mechanical strength and stretchability of the material. An increase in polylactone chain length in LAVE was found to increase strain at break from 25% to 180% and stress at break from 0.34 to 1.41 MPa. The material showed excellent network stability under cyclic strain loading, with no apparent hysteresis. The introduction of disulfide bonds allows the material to self-heal under UV exposure, extending its shelf life. Overall, this work presents an environmentally friendly approach for producing a sustainable elastomer that has potential for use in applications such as intelligent robots, smart wearable technology, and human-machine interfaces.

Heterotelechelic Silicones: Facile Synthesis and Functionalization Using Silane-Based Initiators

The synthetic utility of heterotelechelic polydimethylsiloxane (PDMS) derivatives is limited due to challenges in preparing materials with high chain-end fidelity. In this study, anionic ring-opening polymerization (AROP) of hexamethylcyclotrisiloxane (D3) monomers using a specifically designed silyl hydride (Si-H)-based initiator provides a versatile approach toward a library of heterotelechelic PDMS polymers. A novel initiator, where the Si-H terminal group is connected to a C atom (H-Si-C) and not an O atom (H-Si-O) as in traditional systems, suppresses intermolecular transfer of the Si-H group, leading to heterotelechelic PDMS derivatives with a high degree of control over chain ends. In situ termination of the D3 propagating chain end with commercially available chlorosilanes (alkyl chlorides, methacrylates, and norbornenes) yields an array of chain-end-functionalized PDMS derivatives. This diversity can be further increased by hydrosilylation with functionalized alkenes (alcohols, esters, and epoxides) to generate a library of heterotelechelic PDMS polymers. Due to the living nature of ring-opening polymerization and efficient initiation, narrow-dispersity (Đ < 1.2) polymers spanning a wide range of molar masses (2-11 kg mol-1) were synthesized. With facile access to α-Si-H and ω-norbornene functionalized PDMS macromonomers (H-PDMS-Nb), the synthesis of well-defined supersoft (G' = 30 kPa) PDMS bottlebrush networks, which are difficult to prepare using established strategies, was demonstrated.

Controlled-Radical Polymerization of α-Lipoic Acid: A General Route to Degradable Vinyl Copolymers

Here, we present the synthesis and characterization of statistical and block copolymers containing α-lipoic acid (LA) using reversible addition-fragmentation chain-transfer (RAFT) polymerization. LA, a readily available nutritional supplement, undergoes efficient radical ring-opening copolymerization with vinyl monomers in a controlled manner with predictable molecular weights and low molar-mass dispersities. Because lipoic acid diads present in the resulting copolymers include disulfide bonds, these materials efficiently and rapidly degrade when exposed to mild reducing agents such as tris(2-carboxyethyl)phosphine (Mn = 56 → 3.6 kg mol-1). This scalable and versatile polymerization method affords a facile way to synthesize degradable polymers with controlled architectures, molecular weights, and molar-mass dispersities from α-lipoic acid, a commercially available and renewable monomer.

Emerging Trends in the Chemistry of End-to-End Depolymerization

Over the past couple of decades, polymers that depolymerize end-to-end upon cleavage of their backbone or activation of a terminal functional group, sometimes referred to as "self-immolative" polymers, have been attracting increasing attention. They are of growing interest in the context of enhancing polymer degradability but also in polymer recycling as they allow monomers to be regenerated in a controlled manner under mild conditions. Furthermore, they are highly promising for applications as smart materials due to their ability to provide an amplified response to a specific signal, as a single sensing event is translated into the generation of many small molecules through a cascade of reactions. From a chemistry perspective, end-to-end depolymerization relies on the principles of self-immolative linkers and polymer ceiling temperature (Tc). In this article, we will introduce the key chemical concepts and foundations of the field and then provide our perspective on recent exciting developments. For example, over the past few years, new depolymerizable backbones, including polyacetals, polydisulfides, polyesters, polythioesters, and polyalkenamers, have been developed, while modern approaches to depolymerize conventional backbones such as polymethacrylates have also been introduced. Progress has also been made on the topological evolution of depolymerizable systems, including the introduction of fully depolymerizable block copolymers, hyperbranched polymers, and polymer networks. Furthermore, precision sequence-defined oligomers have been synthesized and studied for data storage and encryption. Finally, our perspectives on future opportunities and challenges in the field will be discussed.

Exploring Lipoic Acid-Mediated Dynamic Bottlebrush Elastomers as a New Platform for the Design of High-Performance Thermally Conductive Materials

The development of high-performance thermally conductive interface materials is the key to unlocking the serious bottleneck of modern microelectronic technology through enhanced heat dispersion. Existing methods that utilize silicone composites rely either on loading large doses of randomly distributed thermal conductive fillers or on filling prealigned thermal conductive scaffolds with liquid silicone precursors. Both approaches suffer from several limitations in terms of physical traits and processability. We describe an alternative approach in which malleable silicone matrices, based on the dynamic cyclic disulfide nature cross-linker (α-lipoic acid), are readily prepared using ring-opening polymerization. The mechanical properties of the resultant dynamic silicone matrix are readily tunable. Stress-dependent depolymerization of the disulfide network demonstrates the ability to reprocess the silicone elastomer matrix, which allows for the fabrication of highly efficient thermal conductive composites with a 3D interconnecting, thermally conductive network (3D-graphite/MxBy composites) via in situ methods. Applications of the composites as thermal dispersion interface materials are demonstrated by LEDs and CPUs, suggesting great potential in advanced electronics.

Mechanisms of Degradation for Polydisulfides: Main Chain Scission, Self-Immolation, Or Chain Transfer Depolymerization

Organic polydisulfides hold immense potential for the design of recyclable materials. Of these, polymers based on lipoic acid are attractive, as they are based on a natural, renewable resource. Herein, we demonstrate that reductive degradation of lipoic acid polydisulfides is a rapid process whereby the quantity of added initiator relative to the polymer content defines the mechanism of polymer degradation, through the main chain scission, self-immolation, or "chain transfer" depolymerization. The latter mechanism is defined as the one during which a thiol group released through the decomposition of one polydisulfide chain initiates depolymerization of the neighbor macromolecule. The chain transfer mechanism afforded the highest yields of recovery of the monomer in its pristine form, and just one molecule of the reducing agent to initiate polymer degradation afforded recovery of over 50% of the monomer. These data are important to facilitate the development of polymer recycling and monomer reuse schemes.

Chemically Recyclable Dithioacetal Polymers via Reversible Entropy-Driven Ring-Opening Polymerization

In a sustainable circular economy, polymers capable of chemical recycling to monomers are highly desirable. We report an efficient monomer-polymer recycling of polydithioacetal (PDTA). Pristine PDTAs were readily synthesized from 3,4,5-trimethoxybenzaldehyde and alkyl dithiols. They then exhibited depolymerizability via ring-closing depolymerization into macrocycles, followed by entropy-driven ring-opening polymerization (ED-ROP) to reform the virgin polymers. High conversions were obtained for both the forward and reverse reactions. Once crosslinked, the network exhibited thermal reprocessability enabled by acid-catalyzed dithioacetal exchange. The network retained the recyclability into macrocyclic monomers in solvent which can repolymerize to regenerate the crosslinked network. These results demonstrated PDTA as a new molecular platform for the design of recyclable polymers and the advantages of ED-ROP for which polymerization is favored at higher temperatures.

Organic-inorganic covalent-ionic molecules for elastic ceramic plastic

Although organic-inorganic hybrid materials have played indispensable roles as mechanical^1-4, optical^5,6, electronic^7,8 and biomedical materials^9-11, isolated organic-inorganic hybrid molecules (at present limited to covalent compounds^12,13) are seldom used to prepare hybrid materials, owing to the distinct behaviours of organic covalent bonds¹⁴ and inorganic ionic bonds¹⁵ in molecular construction. Here we integrate typical covalent and ionic bonds within one molecule to create an organic-inorganic hybrid molecule, which can be used for bottom-up syntheses of hybrid materials. A combination of the organic covalent thioctic acid (TA) and the inorganic ionic calcium carbonate oligomer (CCO) through an acid-base reaction provides a TA-CCO hybrid molecule with the representative molecular formula TA₂Ca(CaCO₃)₂. Its dual reactivity involving copolymerization of the organic TA segment and inorganic CCO segment generates the respective covalent and ionic networks. The two networks are interconnected through TA-CCO complexes to form a covalent-ionic bicontinuous structure within the resulting hybrid material, poly(TA-CCO), which unifies paradoxical mechanical properties. The reversible binding of Ca²⁺-CO₃^2- bonds in the ionic network and S-S bonds in the covalent network ensures material reprocessability with plastic-like mouldability while preserving thermal stability. The coexistence of ceramic-like, rubber-like and plastic-like behaviours within poly(TA-CCO) goes beyond current classifications of materials to generate an 'elastic ceramic plastic'. The bottom-up creation of organic-inorganic hybrid molecules provides a feasible pathway for the molecular engineering of hybrid materials, thereby supplementing the classical methodology used for the manufacture of organic-inorganic hybrid materials.

Self-healing bottlebrush polymer networks enabled via a side-chain interlocking design

Exploring novel healing mechanisms is a constant impetus for the development of self-healing materials. Herein, we find that side-chain interlocking of bottlebrush polymers can form a dynamic network and thereby serve as a driving force for the self-healing process of the materials. Molecular dynamics simulation indicates that the interlocking is formed by the interpenetration between the long side chains of adjacent molecules and stabilized by van der Waals interactions and molecular entanglements of side chains. The interlocking can be tailored by changing the length and density of the side chains through atom transfer radical polymerization. As a result, the optimized bottlebrush polymer shows a healing efficiency of up to 100%. Unlike chemical interactions, side-chain interlocking eliminates the introduction of specific chemical groups. Therefore, bottlebrush polymers can even self-heal under harsh aqueous conditions, including acid and alkali solutions. Moreover, the highly dynamic side-chain interlocking enables bottlebrush polymers to efficiently dissipate vibration energy, and thus they can be used as damping materials. Collectively, side-chain interlocking expands the scope of physical interactions in self-healing materials and hews out a versatile way for polymers to accomplish self-healing capability in various environments.

Mussel-Inspired, Underwater Self-Healing Ionoelastomers Based on α-Lipoic Acid for Iontronics

Weak adhesion and lack of underwater self-healability hinder advancing soft iontronics particularly in wet environments like sweaty skin and biological fluids. Mussel-inspired, liquid-free ionoelastomers are reported based on seminal thermal ring-opening polymerization of a biomass molecule of α-lipoic acid (LA), followed by sequentially incorporating dopamine methacrylamide as a chain extender, N,N'-bis(acryloyl) cystamine, and lithium bis(trifluoromethanesulphonyl) imide (LiTFSI). The ionoelastomers exhibit universal adhesion to 12 substrates in both dry and wet states, superfast self-healing underwater, sensing capability for monitoring human motion, and flame retardancy. The underwater self-repairabilitiy prolongs over three months without deterioration, and sustains even when mechanical properties greatly increase. The unprecedented underwater self-mendability benefits synergistically from the maximized availability of dynamic disulfide bonds and diverse reversible noncovalent interactions endowed by carboxylic groups, catechols, and LiTFSI, along with the prevented depolymerization by LiTFSI and tunability in mechanical strength. The ionic conductivity reaches 1.4 × 10^-6 -2.7 × 10^-5 S m^-1 because of partial dissociation of LiTFSI. The design rationale offers a new route for creating a wide range of LA- and sulfur-derived supramolecular (bio)polymers with superior adhesion, healability, and other functionalities, and thus has technological implications for coatings, adhesives, binders and sealants, biomedical engineering and drug delivery, wearable and flexible electronics, and human-machine interfaces.

On-Demand Cross-Linkable Bottlebrush Polymers for Voltage-Driven Artificial Muscles

Dielectric elastomer actuators (DEAs) generate motion resembling natural muscles in reliability, adaptability, elongation, and frequency of operation. They are highly attractive in implantable soft robots or artificial organs. However, many applications of such devices are hindered by the high driving voltage required for operation, which exceeds the safety threshold for the human body. Although the driving voltage can be reduced by decreasing the thickness and the elastic modulus, soft materials are prone to electromechanical instability (EMI), which causes dielectric breakdown. The elastomers made by cross-linking bottlebrush polymers are promising for achieving DEAs that suppress EMI. In previous work, they were chemically cross-linked using an in situ free-radical UV-induced polymerization, which is oxygen-sensitive and does not allow the formation of thin films. Therefore, the respective actuators were operated at voltages above 4000 V. Herein, macromonomers that can be polymerized by ring-opening metathesis polymerization and subsequently cross-linked via a UV-induced thiol-ene click reaction are developed. They allow us to fast cross-link defect-free thin films with a thickness below 100 μm. The dielectric films give up to 12% lateral actuation at 1000 V and survive more than 10,000 cycles at frequencies up to 10 Hz. The easy and efficient preparation approach of the defect-free thin films under air provides easy accessibility to bottlebrush polymeric materials for future research. Additionally, the desired properties, actuation under low voltage, and long lifetime revealed the potential of the developed materials in soft robotic implantable devices. Furthermore, the C-C double bonds in the polymer backbone allow for chemical modification with polar groups and increase the materials' dielectric permittivity to a value of 5.5, which is the highest value of dielectric permittivity for a cross-linked bottlebrush polymer.

Acid-catalyzed Disulfide-mediated Reversible Polymerization for Recyclable Dynamic Covalent Materials

Poly(1,2-dithiolane)s are a family of intrinsically recyclable polymers due to their dynamic covalent disulfide linkages. Despite the common use of thiolate-initiated anionic ring-opening polymerization (ROP) under basic condition, cationic ROP is still not exploited. Here we report that disulfide bond can act as a proton acceptor, being protonated by acids to form sulfonium cations, which can efficiently initiate the ROP of 1,2-dithiolanes and result in high-molecular-weight (over 1000 kDa) poly(disulfide)s. The reaction can be triggered by adding catalytic amounts of acids and non-coordinating anion salts, and completed in few minutes at room temperature. The acidic conditions allow the applicability for acidic monomers. Importantly, the reaction condition can be under open air without inert protection, enabling the nearly quantitative chemical recycling from bulk materials to original monomers.

Circular Upcycling of Bottlebrush Thermosets

The inability to re-process thermosets hinders their utility and sustainability. An ideal material should combine closed-loop recycling and upcycling capabilities. This trait is realized in polydimethylsiloxane bottlebrush networks using thermoreversible Diels-Alder cycloadditions to enable both reversible disassembly into a polymer melt and on-demand reconfiguration to an elastomer of either lower or higher stiffness. The crosslink density was tuned by loading the functionalized networks with a controlled fraction of dormant crosslinkers and crosslinker scavengers, such as furan-capped bis-maleimide and anthracene, respectively. The resulting modulus variations precisely followed the stoichiometry of activated furan and maleimide moieties, demonstrating the lack of side reactions during reprocessing. The presented circularity concept is independent from the backbone or side chain chemistry, making it potentially applicable to a wide range of brush-like polymers.

Photo-Activity of Silacyclopropenes and their Application in Metal-Free Curing of Silicones

Silicone elastomers are usually produced via addition or condensation curing by means of platinum- or tin-based catalysis. The employed catalysts remain in the final rubber and cannot be recovered, thus creating various economic and environmental challenges. Herein, a light-mediated curing method using multifunctional silacyclopropenes as crosslinker structures was introduced to create an effective alternative to the conventional industrial crosslinking. To evaluate the potential of the photoreaction a model study with small monofunctional silirenes was conducted. These investigations confirmed the required coupling reactivity upon irradiation and revealed an undesired rearrangement formation. Further optimization showed the reaction selectivity to be strongly influenced by the substitution of the three-membered ring system and the reaction temperature. The synthesis of multifunctional silirenes was described based on the most suitable model compound to create active crosslinker scaffolds for their application in silicone curing. This photo-controlled process produces catalyst and additive free elastomers from liquid silicones, including hydride-, hydroxy-, or vinyl terminated polydimethylsiloxanes.