Highly stretchable covalent adaptive networks enabled by dynamic boronic diester linkages with nitrogen→boron coordination

Dynamic Boronic Ester Cross-Linked Polymers with Tunable Properties via Side-Group Engineering

The development of dynamic covalent materials with repairability, reprocessability, and recyclability is crucial for sustainable development. In this work, we report a new strategy to adjust the thermomechanical properties of boronic ester cross-linked poly(β-hydroxyl amine)s through side-group engineering. By tuning the side groups of the poly(β-hydroxyl amine)s, we have developed self-healable, reprocessable, and shape-programmable materials. By tuning the side groups of the poly(β-hydroxyl amine)s, the thermomechanical properties can be readily adjusted. Notably, the 3-amino-1,2-propanediol-derived polymer exhibits enhanced thermal (Tg = 95 °C) and mechanical (tensile strength = 34.2 MPa) performance due to increased hydrogen bonding. Benefiting from the dynamic reversibility of the boronic esters, these materials demonstrate solvent-assisted healing, reprocessing, chemical recycling, and shape programming capabilities. Given their straightforward synthesis, tunable properties, and robust dynamic features, the boronic ester cross-linked poly(β-hydroxyl amine)s hold great promise for various applications, including flexible electronic and biomedical materials.

Au nanozyme-based multifunctional hydrogel for inflammation visible monitoring and treatment

Chronic inflammation can delay wound healing, eventually leading to tissue necrosis and even cancer. Developing real-time intelligent inflammation monitoring and treatment to achieve effective wound management is important to promote wound healing. In this study, a smart multifunctional hydrogel (Hydrogel@Au NCs&DG) was proposed to monitor and treat the wound inflammation. It was prepared by mixing 3-carboxy-phenylboronic acid modified chitosan (CS-cPBA), β-glycerophosphate (β-GP), albumin-protected gold nanoclusters (BSA-Au NCs), and dipotassium glycyrrhizinate (DG) about 10 s. In this hydrogel, CS-cPBA and β-GP are crosslinked together by boric acid ester bond and hydrogen bond to form the main hydrogel network, endowing the hydrogel with self-healing and injectable properties to adapt irregular wounds. Importantly, the as-prepared hydrogel with good biocompatibility and excellent adhesion property could directly determine the H2O2 to monitor the wound microenvironment by visible fluorescence change of BSA-Au NCs and then guide the frequency of dressing change to eliminate inflammation. The results demonstrated that the as-prepared smart hydrogel could be expected to serve as an intelligent wound dressing to promote inflammation-infected wound healing.

Rapid Stress Relaxation, Multistimuli-Responsive Elastomer Based on Dual-Dynamic Covalent Bonds and Aniline Trimer

Covalent adaptable networks (CANs) are an emerging kind of smart materials in which cross-links are reversible upon some stimuli and then provide malleability and a stimuli-responsive ability to the materials. There is a trend to endow CANs with multistimuli-responsive capabilities and rapid stress relaxation to pursue more advanced applications. To integrate these two features into one material, here, dual-dynamic covalent bonds (imines and boronic esters) and aniline trimer (ACAT) were incorporated into the styrene butadiene elastomer as dynamic cross-links. The obtained CANs were demonstrated with rapid stress relaxation and a relatively low activation energy of 36 ± 1 kJ mol^-1, resulting from the synergistic effect of dual-dynamic covalent bonds to rearrange the network at a faster rate than for either imines or boronic esters. Because of the dynamic nature of imines or boronic esters, the elastomer can be recycled upon heat. Moreover, the appearance and configuration of the elastomer could also be manipulated by pH and light because of the inclusion of ACAT. All in all, the coupled multistimuli-responsive behavior and rapid stress relaxation in one single elastomer would potentially be applicable for sensors and actuators with good recyclability.

Hydroxyl-Terminated Polybutadiene-Based Polyurethane with Self-Healing and Reprocessing Capabilities

Hydroxyl-terminated polybutadiene (HTPB)-based polyurethane (PU) networks play indispensable roles in a variety of applications; however, they cannot be reprocessed, resulting in environmental problems and unsustainable industrial development. In this work, recyclable HTPB-based PU vitrimer (HTPB-PUV) networks are fabricated by introduction of a cross-linker 2,2'-(1,4-phenylene)-bis[4-mercaptan-1,3,2-dioxaborolane] (BDB) with dynamic boronic ester bonds into the network. Meanwhile, the BDB can stabilize the HTPB unit in the network by elimination of double bonds. The novel HTPB-PUV networks are constructed by a thiol-ene "click" reaction and an addition reaction between HTPB and cross-linker BDB and isocyanates (HDI). The dynamic HTPB-PUV networks are characterized by dynamic mechanical analysis (DMA) and Fourier transform infrared (FTIR). The obtained dynamic HTPB-PUV networks possess superior thermostability. Moreover, due to the presence of dynamic boronic ester bonds, the HTPB-PUV network topologies can be altered, contributing to the reprocessing, self-healing, and welding abilities of the final polymer. Through a hot press, the pulverized sample can be reprocessed for several cycles, and mechanical properties of the reprocessed samples are similar to those of the pristine one, with the tensile strength being even higher. The self-healed sample exhibits almost complete recovery from scratch after the healing treatment at 130 °C for 3 h. Moreover, a welding efficiency of 120% was achieved.