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Design and closed-loop chemical recycling of cross-linked polymeric materials Schematic of (a) maleic acid tertiary amide bonds constructed from maleic anhydrides and secondary amines; and (b) polymer networks prepared from bifunctional maleic anhydrides and multifunctional secondary amines and their depolymerization in acid aqueous solution. Two monomers can be separated and regained in a closed-looped recycling process.
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Closed-loop chemical recycling provides a solution to the end-of-use problem of synthetic polymers. However, it remains a major challenge to design dynamic bonds, capable of effective bonding and reversible cleaving, for preparing chemically recyclable cross-linked polymers. Herein, we report a dynamic maleic acid tertiary amide bond based upon rev...
Citations
... The storage modulus and T g of the chemically recycled EN-VanEHBP7 were also almost the same as those of the original samples, exhibiting excellent room-temperature closed-loop recyclability. Figure 8g shows that among all the samples, EN-VanEHBP7 exhibited the highest tensile strength and could be recycled at room temperature 2,22,[36][37][38][39][40][41][42][43][44][45] . ...
The regulation of topological structure of covalent adaptable networks (CANs) remains a challenge for epoxy CANs. Here, we report a strategy to develop strong and tough epoxy supramolecular thermosets with rapid reprocessability and room-temperature closed-loop recyclability. These thermosets were constructed from vanillin-based hyperbranched epoxy resin (VanEHBP) through the introduction of intermolecular hydrogen bonds and dual dynamic covalent bonds, as well as the formation of intramolecular and intermolecular cavities. The supramolecular structures confer remarkable energy dissipation capability of thermosets, leading to high toughness and strength. Due to the dynamic imine exchange and reversible noncovalent crosslinks, the thermosets can be rapidly and effectively reprocessed at 120 °C within 30 s. Importantly, the thermosets can be efficiently depolymerized at room temperature, and the recovered materials retain the structural integrity and mechanical properties of the original samples. This strategy may be employed to design tough, closed-loop recyclable epoxy thermosets for practical applications.
... Synergistic effects of using covalent and non-covalent systems are beneficial to improve the robustness and meanwhile retain the dynamic characteristics of supramolecular polymers [34][35][36] . Such polymeric networks crosslinked by supramolecular interactions [37][38][39][40] , dynamic covalent bonds 41 or mechanically interlocked bonds [42][43][44] were proven to have intriguing properties that cannot be acquired by covalently crosslinked polymers. Owing to the relative weakness of single supramolecular interactions, multiple and strong interactions are preferable in the crosslinkers. ...
Supramolecular polymeric materials have exhibited attractive features such as self-healing, reversibility, and stimuli-responsiveness. However, on account of the weak bonding nature of most noncovalent interactions, it remains a great challenge to construct supramolecular polymeric materials with high robustness. Moreover, high usage of supramolecular units is usually necessary to promote the formation of robust supramolecular polymeric materials, which restrains their applications. Herein, we describe the construction of highly robust supramolecular polymer networks by using only a tiny amount of metallacycles as the supramolecular crosslinkers. A norbornene ring-opening metathesis copolymer with a 120° dipyridine ligand is prepared and self-assembled with a 60° or 120° Pt(II) acceptor to fabricate the metallacycle-crosslinked polymer networks. With only 0.28 mol% or less pendant dipyridine units to form the metallacycle crosslinkers, the mechanical properties of the polymers are significantly enhanced. The tensile strengths, Young’s moduli, and toughness of the reinforced polymers reach up to more than 20 MPa, 600 MPa, and 150 MJ/m³, respectively. Controllable destruction and reconstruction of the metallacycle-crosslinked polymer networks are further demonstrated by the sequential addition of tetrabutylammonium bromide and silver triflate, indicative of good stimuli-responsiveness of the networks. These remarkable performances are attributed to the thermodynamically stable, but dynamic metallacycle-based supramolecular coordination complexes that offer strong linkages with good adaptive characteristics.
... 60,64−66,103,113,118−120 Only a few studies have demonstrated both 90+% small-molecule recovery yield and full property recovery after reprocessing of vitrimers or CANs. [64][65][66]103,118 The remarkable 94 mol % yield of a pure small molecule demonstrates that trans(thio)carbamoylation is a promising approach for achieving circularity with NIPTU. ...
... The storage modulus and T g of the chemically recycled EN-VanEHBP7 were also almost the same as those of the original samples, exhibiting excellent room-temperature closed-loop recyclability. Figure 8g shows that among all the samples, EN-VanEHBP7 exhibited the highest tensile strength and could be recycled at room temperature 2,22,[36][37][38][39][40][41][42][43][44][45] . ...
Covalent adaptable networks are critical for the recycling and reuse of cross-linked epoxy thermosets. However, a major challenge is to develop efficient recyclable strategies while maintaining the high-performance of epoxy thermosets. Here, we synthesized vanillin-based hyperbranched epoxy resin (VanEHBP) to prepare tough epoxy supramolecular thermosets. The supramolecular structures were constructed with VanEHBP via intermolecular hydrogen bonds, intramolecular and intermolecular cavities, dual dynamic covalent bonds (imine exchange and transesterification). The epoxy thermosets exhibited excellent mechanical properties, as well as fast reprocessability, which can be reprocessed at 120°C within 30 sec and maintain about 100% of tensile strength. Importantly, the epoxy thermosets can be easily fully recycled under room temperature and the recovered materials can preserve 93.5% of mechanical properties of the original samples. This wok represents a unique strategy for developing room-temperature closed-loop recyclable epoxy thermosets with superior comprehensive performance and promising practical application prospects.
... Thus, it remains a major challenge to design dynamic bonds, capable of effective bonding and reversible cleaving, for preparing chemically recyclable cross-linked polymers. To resolve this issue, Qin et al. have developed chemically recyclable cross-linked polyamic acid materials through the incorporation of dynamic maleic acid tertiary amide bonds (Figure 5d) [116]. The dynamic maleic acid tertiary amide bond is based upon a reversible amidation reaction between maleic anhydrides and secondary amines, enabling reversible chemical control over depolymerization of the resulting polymer networks. ...
Ranging from traditional food packaging, clothing, and furniture to the current small and large electronic devices and automobiles, plastics serve to fulfill diverse demands in our daily lives. However, the global plastic waste generation is dramatically escalating, currently standing at approximately 150 million metric tonnes annually. While some of regenerated plastics recycled by mechanical methods can be used as their parent plastics, cost and energy savings are limited by multiple preliminary processes such as plastic sorting, shredding, washing, and drying. Moreover, the continuous mechanical recycling process degrades the physical properties of the materials. In this context, chemical recycling is emerging as a promising alternative method due to its high efficiency, simple preliminary steps, reducing reliance on fossil resources, and conversion of plastic waste into value-added chemicals. This review provides a state-of-the-art overview of contemporary chemical recycling of polymeric materials via i) depolymerization: “polymers to small valuable molecules” and ii) closed-loop cycles: “polymers to monomers, and/or to polymers”, by encompassing both traditional/advanced depolymerization chemistries and the remaining challenges. These recycling approaches are contextualized within the present industrial technologies, key design principles, and specific recycling case studies related to distinct polymeric materials.
... In addition to the dynamic bonds of transesterification first proposed by Leibler, a variety of dynamic bonds such as disulfide bonds (Mauro et al., 2020;Lee et al., 2019;Liu et al., 2020), hindered urea bonds Zhang et al., 2022), DA reactions (Berto et al., 2018;Tremblay-Parrado et al., 2021), and Schiff bases (Hong et al., 2022;Memon et al., 2020;Zhao et al., 2022a;Zhao et al., 2023a) are used in the preparation of vitrimers. The above dynamic bonds can undergo dynamic exchange reactions under external stimuli (such as light, heat, pH) and realize closed-loop chemical recycling of polymers through the rearrangement of topological networks (Christensen et al., 2019;Qin et al., 2022). Among various dynamic bonds, the imine bond, also named the Schiff base, has attracted much attention, because it can be exchanged without catalyst required at elevated temperature and can be dissociated under or polar solvent. ...
Traditional thermosetting materials cannot be degraded, recycled, or reprocessed once they attain their end-oflife causing environmental pollution. Using renewable feedstocks to develop covalent adaptive networks (CANs) based on dynamic covalent bonds can make up for the above shortcomings. The design of new polymeric materials using renewable feedstocks is consistent with the concept of sustainability practices. Herein, castor oil, cysteamine and vanillin are used as building blocks to construct fully bio-based thermosetting polyimine vitrimers
through imination between cysteamine functionalized castor oil and divanillin. Owing to its unique structure containing flexible chains, aromatic hydrocarbon and imine bonds, polyimine vitrimers integrate fine mechanical properties, good thermal stability, excellent adhesion, rapid self-healing performance, degradability,
recyclability and antibacterial ability. Specifically, the tensile strength of 5.21 MPa, lap-shear strength of 6.07 MPa on 304 stainless steels, self-healing within 30 min at 80 ◦C, and antibacterial rate against Staphylococcus aureus and Escherichia coli > 90% are observed for this fully bio-based polyimine vitrimers. Additionally, discarded
materials can be recovered multiple times for repeated usage by thermo-compression reprocessing and
solvent treatment. The original monomer DV is obtained by degradation under 1 M aqueous acetic acid solution with a recovery rate of 92.7%. Therefore, this work will provide a new research strategy for the application of multifunctional bio-based polymer materials, especially in adhesives.
... We mentioned [71] one example above of the mechanosynthesis of diketoenamine-bond-connected polymers for ready mechanopolymerization/depolymerization at room temperature. Very recently, another type of roomtemperature-recyclable polymer containing dynamic maleic acid tertiary amide bonds was reported [183]. ...
... We mentioned [71] one example above of the mechanosynthesis of diketoenamine-bond-connected polymers for ready mechanopolymerization/depolymerization at room temperature. Very recently, another type of roomtemperature-recyclable polymer containing dynamic maleic acid tertiary amide bonds was reported [183]. ...
... We mentioned [71] one example above of the mechanosynthesis of diketoenamine-bond-connected polymers for ready mechanopolymerization/depolymerization at room temperature. Very recently, another type of roomtemperature-recyclable polymer containing dynamic maleic acid tertiary amide bonds was reported [183]. ...
Abstract: Mechanochemically induced methods are commonly used for the depolymerization of polymers, including plastic and agricultural wastes. So far, these methods have rarely been used for polymer synthesis. Compared to conventional polymerization in solutions, mechanochemical polymerization offers numerous advantages such as less or no solvent consumption, the accessibility
of novel structures, the inclusion of co-polymers and post-modified polymers, and, most importantly, the avoidance of problems posed by low monomer/oligomer solubility and fast precipitation during polymerization. Consequently, the development of new functional polymers and materials, including those based on mechanochemically synthesized polymers, has drawn much interest, particularly
from the perspective of green chemistry. In this review, we tried to highlight the most representative examples of transition-metal (TM)-free and TM-catalyzed mechanosynthesis of some functional polymers, such as semiconductive polymers, porous polymeric materials, sensory materials, materials for photovoltaics, etc.
Plastics, renowned for their outstanding properties and extensive applications, assume an indispensable and irreplaceable role in modern society. However, the ubiquitous consumption of plastic items has led to a growing accumulation of plastic waste. Unreasonable practices in the production, utilization, and recycling of plastics have led to substantial energy resource depletion and environmental pollution. Herein, the state‐of‐the‐art advancements in the lifecycle management of plastics are timely reviewed. Unlike typical reviews focused on plastic recycling, this work presents an in‐depth analysis of the entire lifecycle of plastics, covering the whole process from synthesis, processing, to ultimate disposal. The primary emphasis lies on selecting judicious strategies and methodologies at each lifecycle stage to mitigate the adverse environmental impact of waste plastics. Specifically, the article delineates the rationale, methods, and advancements realized in various lifecycle stages through both physical and chemical recycling pathways. The focal point is the attainment of optimal recycling rates for waste plastics, thereby alleviating the ecological burden of plastic pollution. By scrutinizing the entire lifecycle of plastics, the article aims to furnish comprehensive solutions for reducing plastic pollution and fostering sustainability across all facets of plastic production, utilization, and disposal.
