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Epoxy vitrimer is a kind of recyclable polymer that can reconstruct their network topology through chemical bond exchange reactions, providing an innovative solution for the thermosets recycling dilemma. However, current vitrimers have not yet reached the level of commercial epoxy resins, especially in performance and preparation process. In this study, high-performance epoxy vitrimer has been prepared using a commercial epoxy-anhydride. In the presence of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as an internal catalyst, both mechanical and thermal properties were improved significantly because of the complete curing reaction facilitated by TBD. With the addition of catalyst TBD, the tensile strength, modulus, elongation at break and the glass transition temperature (Tg) of materials increased from 49.12 to 79.27 MPa, 2080.96 to 2266.19 MPa, 2.78% to 3.86%, and 94°C to 132°C respectively. Meanwhile, the network rearrangement rate improved, in which the stress relaxation time (τ*) of networks declined from 19 min to 10 min at 200°C. Taking advantages of dynamic properties, these vitrimers can be reshaped and chemically degraded. Furthermore, carbon fiber composites are fabricated by using vitrimer as matrix, which can be successfully recycled with chemical degradation process at 160°C within 1 h. This research facilitates the development of recyclable epoxy and composites that exhibits significant potential for commercial applications.

ABSTRACTFor sustainable application of chloroprene rubber (CR), a new technology is developed by the vulcanization of CR using 2,2’-dithiodipyridine (DPD) as a cross-linking agent with the reprocessing performance owing to disulfide metathesis. When DPD was incorporated into CR vulcanization, the Menschutkin reaction between allyl chloride group and pyridine group occurred with a maximum exothermic peak at 184°C. The number of effective cross-linking bond at 0.5 phr DPD vulcanizate was higher than that at high DPD content. This vulcanizate showed high tensile strength (11.12 MPa) and elongation at break (1253 ± 120%) owing to the exchangeable disulfide bond in the system. Under the catalysis of triphenylphosphine, the metathesis of disulfide compound was improved obviously, which endowed CR/DPD vulcanizates with good recyclability performance. Disulfide cross-linkage maintains its stability at low temperature, thus ensuring the mechanical stability of CR/DPD vulcanizate under the ambient conditions. Vulcanization and reprocessing of CR/DPD vulcanizate can be conducted with common industrial rubber processing equipment. Such reprocessable chloroprene rubber could have potential application in CR industry, also serve to significantly improve environmental sustainability.

Abstract To minimize the environmental pollution caused by polymeric waste, materials based dynamic chemistry have attracted extensive attention around the world. Various dynamic covalent bonds or noncovalent interactions have been employed to design multifunctional polymers with recyclability, reprocessablility, and sustainability. Among them, polymers based on reversible boron–oxygen (B–O) bonds have been widely investigated because of their unique properties. Particularly, lots of scientists have demonstrated that the combination with boron–nitrogen (B–N) coordination can effectively accelerate the dynamicity as well as enhance the stability of B–O bonds. Therefore, numerous polymers containing dynamic B–O bonds with dative B–N coordination have been designed and synthesized in recent years. These polymers exhibit excellent versatility and great potential for diverse applications such as biosensors, battery electrolytes, and artificial skins. This review provides an overview of the comprehensive influence of dynamic B–N coordination chemistry on B–O bonds in organoboron species and highlights the developments in the area of constructing boron‐containing polymeric materials with this interesting linkage. The design guidelines, existing challenges, and future perspectives in this burgeoning field are discussed and proposed.

In the present work a recyclable and reprocessable vitrimer suitable for pultrusion process has been formulated and a pultruded profile reshaped by thermoforming has been manufactured therefrom. A DGEBA epoxy resin with medium range viscosity and a bis(a-aminophenyl disulfide) as dynamic crosslinker were used for the synthesis of the vitrimer. The thermal stability was studied by thermogravimetric analysis (TGA) and curing behaviour and curing kinetics were studied by means of dynamic scanning calorimeter (DSC) and rheology measurements. Mechanical properties of the dynamic resins and its counterpart epoxy resin and of the fabricated carbon fibre reinforced polymers (CFRP) were determined. The dynamic resin showed a fast stress relaxation at temperatures above 150 °C. Finally, as a proof of concept, mechanical recyclability and the thermoforming of the vitrimer-based pultruded profile have been validated.

Photoactuators are promising smart materials that can adapt their shapes upon light illumination. Smart materials with recycling, reusable, and reconfigurable properties are crucial for a sustainable society, and it is important to expand their function. Recently, much effort was made to address the issue of reprocessability and recyclability of photoactuators. Based on the development of polymer chemistry, supramolecular chemistry, and dynamic covalent chemistry, it is now possible to prepare reconfigurable and recyclable photoactuators using azobenzene-containing polymers (azopolymers). Herein, the recent advances on reconfigurable and reprocessable photoactuators, including dynamic crosslinked networks systems and non-covalently crosslinked azobenzene-containing polymers, were reviewed. We discuss the challenges in the field as well as the directions for the development of such photoactuators.

Photodeformable azobenzene (azo) polymers are a class of smart polymers that can efficiently convert light energy into mechanical power, holding great promise in various photoactuating applications. They are typically of crosslinked polymer networks with highly oriented azo mesogens embedded inside. Upon exposure to the light of appropriate wavelength, they experience dramatic order parameter change following the configuration change of the azo units. This could result in the generation and accumulation of the gradient microscopic photomechanical force in the crosslinked polymer networks, thus leading to their macroscopic deformation. So far, a great number of photodeformable azo polymers have been developed, including some unoriented ones showing photodeformation based on different mechanisms. Among them, photodeformable azo polymers with dynamic crosslinking networks (and some uncrosslinked ones) have aroused particular interest recently because of their obvious advantages over those with stable chemical crosslinking structures such as high recyclability and reprocessability. In this paper, I provide a detailed overview of the recent progress in such reprocessable photodeformable polymers. In addition, some challenges and perspectives are also presented.