Self-Healable and Recyclable Dynamic Covalent Networks Based on Room Temperature Exchangeable Hydrazide Michael Adduct Linkages

Non-activated Esters as Reactive Handles in Direct Post-Polymerization Modification

Non-activated esters are prominently featured functional groups in polymer science, as ester functional monomers display great structural diversity and excellent compatibility with a wide range of polymerization mechanisms. Yet, their direct use as a reactive handle in post-polymerization modification has been typically avoided due to their low reactivity, which impairs the quantitative conversion typically desired in post-polymerization modification reactions. While activated ester approaches are a well-established alternative, the modification of non-activated esters remains a synthetic and economically valuable opportunity. In this review, we discuss past and recent efforts in the utilization of non-activated ester groups as a reactive handle to facilitate transesterification and aminolysis/amidation reactions, and the potential of the developed methodologies in the context of macromolecular engineering.

Degradation of aniline: sodium alginate/modified pomelo cellulose double cross-linking system as a bacterial immobilization carrier

Pectin cellulose grafted with glycidyltrimethylammoniochloride (GTMAC) was successfully obtained following the processes of depectinfibrillation and cellulose cationization using ordinary Shatian pomelo peel produced in Yongzhou, Hunan, as the raw material. This is the first report on a new type of functionalized sodium alginate-immobilized material prepared from the fibers of pomelo peel. The material was prepared by combining modified pomelo peel cellulose and sodium alginate following the processes of physical and chemical double cross-linking. The prepared material was used to embed the target bacteria to achieve the biodegradation of p-aniline. The concentration of CaCl₂ was adjusted when the alginate gelled, and the alginate to yuzu peel cellulose ratio was tuned. The immobilized material-embedded bacteria help achieve the best degradation effect. Bacteria are embedded during the process of the degradation of aniline wastewater, and the functionalization of the cellulose/sodium alginate-immobilized material results in unique surface structure performance. The performance of the prepared system is better than that of the single sodium alginate-based material characterized by a large surface area and good mechanical properties. The degradation efficiency of the system is improved significantly for the cellulose materials, and the prepared materials can potentially find applications in the field of bacteria-fixed technology.

Strong, Healable, Stimulus-Responsive Fluorescent Elastomers Based on Assembled Borate Dynamic Nanostructures

Self-healing materials integrated with robust mechanical property and fascinating functions synchronously hold great prospects in many applications, but it still remains a grand challenge. Here, a bottom-up assembly method of preparing borate dynamic nanostructures (BDN) with controllable morphologies and interfacial crosslinks is proposed, from which a robust self-healing elastomer is fabricated. The BDN is optimized to construct dense and strong interfacial boronic easter crosslinks, endowing the elastomer with outstanding stretchability (2050%), high strength (17.9 MPa) as well as healing efficiency (77.1%). Moreover, the elastomer also exhibits pH stimulus-responsive fluorescence property and excellent functional repairability, enabling its potential application in intelligent material fields such as information encoding and encryption. This study demonstrates a general approach to produce self-healable functional materials with robust mechanical properties, and defines a rich platform for exploring various functional nanostructured materials.

A NIR laser induced self-healing PDMS/Gold nanoparticles conductive elastomer for wearable sensor

Self-healing conductive elastomers have been widely used in smart electronic devices, such as wearable sensors. However, nano fillers hinder the flow of polymer segments, which make the development of conductive elastomer with rapid repair and high ductility a challenge. In this work, thioctic acid (TA) was grafted onto amino-modified polysiloxane (PDMS-NH₂) by dehydration condensation of amino group and carboxyl group. By introducing gold nanoparticles, a dynamic network based on S-Au interaction was constructed. The dynamic gold cross-linking could effectively dissipate the energy exerted by external force and improve the extensibility of conductive elastomer. In addition, S-Au interaction had a good optothermal effect, so that the elastomer rapidly healed under NIR irradiation, and the repair efficiency reached 92%. We further evaluated the performance of the conductive elastomer as a strain sensor. The sample could accurately monitor the bending of human joints and small muscle state changes. This kind of self-healable conductive elastomer based on dynamic S-Au interaction has great potential in the fields of interpersonal interaction and health monitoring.

Catalyst-free room-temperature self-healing polymer networks based on dynamic covalent quinone methide-secondary amine chemistry

A novel type of dynamic covalent polymer network with a catalyst-free room-temperature self-healing ability was developed on a new dynamic covalent chemistry of aza-Michael addition between para-quinone methide and secondary amine.

Self-Healing Ti3C2 MXene/PDMS Supramolecular Elastomers Based on Small Biomolecules Modification for Wearable Sensors

Flexible conductive composites can be used as wearable strain sensors, which are widely used in the fields of new-generation robotics, electronic skin, and human detection. However, how to make conductive composites that simultaneously possess flexibility, stretchability, self-healing, and sensing capability is challenging research. In this work, we innovatively designed and prepared a silicone polymer conductive composite. MXenes and amino poly(dimethylsiloxane) were modified by small biomolecules via an esterification reaction and a Schiff base reaction, respectively. The modified MXenes are uniformly dispersed, which endows the composite with good electrical conductivity. The reversibility of multiple hydrogen bonds and imine bonds in the composite system makes it have ideal tensile properties and high-efficiency self-healing ability without external stimulation. The conductive composite containing 10 wt % A-MXenes showed an elongation of 81%, and its mechanical strength could reach 1.81 MPa. After repair, the tensile properties and the electrical conductivity could be restored to 98.4 and 97.6%, respectively. In addition, the conductive composite is further evaluated for the value of wearable strain sensors. Even after cut-healed processes, the conductive composite can still accurately detect tiny human movements (including speaking, swallowing, and pressing). This kind of self-healing MXene/PDMS elastomers based on the modification of small biomolecules has great potential as wearable strain sensors. This simple preparation method provides guidance for future multifunctional flexible electronic materials.

Fluorodynamers Displaying Tunable Fluorescence on Constitutional Exchanges in Solution and at Solid Film-Solution Interface

Dynamic covalent polymers-dynamers-are adaptive materials that offer timely variant adaptive macroscopic organization across extended scales. In the current study, imine exchange reactions and fluorescence transfer can occur at the interfaces between various solutions and solid state dynameric films. The fluorescence quenching upon imine formations for designed fluorogen was successfully demonstrated, and this tunable fluorescence was further used to study the re-composition of a solid film. Moreover, the dynamic covalent films also exhibited responsiveness to competing amines and acid/base conditions, both in solutions and solid film-solution interface. This work can provide more insights into interface dynamic chemistry and holds great potential for further applications in optical and biomedical materials.

Dynamic Covalent Polymers for Biomedical Applications

The rapid development of supramolecular polymer chemistry and constitutional dynamic chemistry over the last decades has made tremendous impact on the emergence of dynamic covalent polymers. These materials are formed through reversible covalent bonds, endowing them with adaptive and responsive features that have resulted in high interest throughout the community. Owing to their intriguing properties, such as self-healing, shape-memory effects, recyclability, degradability, stimuli-responsiveness, etc., the materials have found multiple uses in a wide range of areas. Of special interest is their increasing use for biomedical applications, and many examples have been demonstrated in recent years. These materials have thus been used for the recognition and sensing of biologically active compounds, for the modulation of enzyme activity, for gene delivery, and as materials for cell culture, delivery, and wound-dressing. In this review, some of these endeavors are discussed, highlighting the many advantages and unique properties of dynamic covalent polymers for use in biology and biomedicine.

Solvent processable and recyclable covalent adaptable organogels based on dynamic trans-esterification chemistry: separation of toluene from azeotropic mixtures

New covalent adaptable networks (CANs) possessing processability and recyclability to monomers are desirable as an alternative to traditional plastics to address plastic waste-related issues.

Catalyst-free, aza-Michael polymerization of hydrazides: polymerizability, kinetics, and mechanistic origin of an α-effect

Despite the powerful nature of the aza-Michael reaction for generating C-N linkages and bioactive moieties, the bis-Michael addition of 1° amines remains ineffective for the synthesis of functional, step-growth polymers due to the drastic reduction in reactivity of the resulting 2° amine mono-addition adduct. In this study, a wide range of commercial hydrazides are shown to effectively undergo the bis-Michael reaction with divinyl sulfone (DVS) and 1,6-hexanediol diacrylate (HDA) under catalyst-free, thermal conditions to afford moderate to high molecular weight polymers with M n = 3.8-34.5 kg mol-1. The hydrazide-Michael reactions exhibit two distinctive, conversion-dependent kinetic regimes that are 2nd-order overall, in contrast to the 3rd-order nature of amines previously reported. The mono-addition rate constant was found to be 37-fold greater than that of the bis-addition at 80 °C for the reaction between benzhydrazide and DVS. A significant majority (12 of 15) of the hydrazide derivatives used here show excellent bis-Michael reactivity and achieve >97% conversions after 5 days. This behavior is consistent with calculations that show minimal variance of electron density on the N-nucleophile among the derivatives studied. Reactivity differences between hydrazides and hexylamine are also explored. Overall, the difference in reactivity between hydrazides and amines is attributed to the adjacent nitrogen atom in hydrazides that acts as an efficient hydrogen-bond donor that facilitates intramolecular proton-transfer following the formation of the zwitterion intermediate. This effect not only activates the Michael acceptor but also coordinates with additional Michael acceptors to form an intermolecular reactant complex.