Dynamic crosslinking compatibilizes immiscible mixed plastics

Ultra-Fast Selenol-Yne Click (SYC) Reaction Enables Poly(selenoacetal) Covalent Adaptable Network Formation

The emergence of covalent adaptable networks (CANs) based on dynamic covalent bonds (DCBs) presents a promising avenue for achieving resource recovery and utilization. In this study, we discovered a dynamic covalent bond called selenacetal, which is obtained through a double click reaction between selenol and activated alkynes. Density functional theory (DFT) calculations demonstrated that the ΔG for the formation of selenoacetals ranges from 12 to 18 kJ mol-1, suggesting its potential for dynamic reversibility. Dynamic exchange experiments involving small molecules and polymers provide substantial evidence supporting the dynamic exchange properties of selenoacetals. By utilizing this highly efficient click reaction, we successfully synthesized dynamic materials based on selenoacetal with remarkable reprocessing capabilities without any catalysts. These materials exhibit chemical recycling under alkaline conditions, wherein selenoacetal (SA) can decompose into active enone selenide (ES) and diselenides. Reintroducing selenol initiates a renewed reaction with the enone selenide, facilitating material recycling and yielding a newly developed dynamic material exhibiting both photo- and thermal responsiveness. The results underscore the potential of selenoacetal polymers in terms of recyclability and selective degradation, making them a valuable addition to conventional covalent adaptable networks.

Closed-loop chemically recyclable covalent adaptive networks derived from elementary sulfur

The development of sulfur-rich polymers derived from elementary sulfur provides an innovative approach to industrial waste valorization. Despite significant advancements in polymerization techniques and promising applications beyond traditional polymers, polysulfide networks are still primarily stabilized by diene crosslinkers, forming robust C-S bonds that hinder the degradation of sulfur-based polymers. In this study, the anionic ring-opening copolymerization of chemically homologous S8 and cyclic disulfides was explored to yield robust sulfur-rich copolymers with high molecular weight. The incorporation of polysulfide segments not only efficiently activated the crosslinked networks for excellent reprocessability and mechanical adaptability but also endowed the resulting copolymer with high optical transparency in the near-infrared region. More importantly, the dynamic disulfide crosslinking sites promoted the chemical closed-loop recyclability of the polysulfide networks via reversible S-S cleavage. This innovative inverse vulcanization strategy utilizing dynamic disulfide crosslinkers offers a promising pathway for the advanced applications and upcycling of high-performance sulfur-rich polymers.

Simultaneously Flame Retarding and Toughening of Epoxy Resin Composites Based on Two-Dimensional Polyhedral Oligomeric Silsesquioxane/Polyoxometalate Supramolecular Nanocrystals with Ultralow Loading

For industrial practical applications, it is difficult to simultaneously endow epoxy resin (EP) composites with superior flame retardancy, smoke suppression, toughness, and low-dielectric constants. Herein, unique polyhedral oligomeric silsesquioxane/polyoxometalate (POM(Mo)-POSS(ibu-Li)) nanosheets were synthesized via a simple one-pot method using laboratory-made lithium-containing hepta-isobutyl-POSS (ibu-Li-POSS) and the low-cost industrial chromogenic agent H3PMo12O40 as raw materials. The incorporation of 2 wt % POM(Mo)-POSS(ibu-Li) nanoflakes into EP significantly enhanced the compatibility between nanoadditives and the EP matrix. Compared with EP, the flexural and impact strengths increased by 36.2 and 78.2%, respectively. Therefore, POM(Mo)-POSS(ibu-Li) has significant advantages in enhancing the toughness of EP compared with existing flame retardants. The dielectric constant and loss were apparently reduced to meet the increasing requirements of EP-type electronic packaging materials and components. Notably, the synthesized POM(Mo)-POSS(ibu-Li) contained various flame-retardant and smoke-suppression elements such as P, Mo, and Si. The ultralow loading (2 wt %) of POM(Mo)-POSS(ibu-Li) significantly reduced the peak heat release rate, peak of smoke production rate, and CO production rate by 43.9, 40.6, and 65.8%, respectively. Meanwhile, the value of LOI increased directly from 24.0% for EP to 30.2% and passed the V-0 rating in the UL-94 test. However, incorporating 5 wt % POSS derivatives into EP alone to ensure that the prepared composites pass the V-0 rating of the UL-94 test has always been an extraordinarily difficult problem. Therefore, the dilemmas of poor dielectric properties, inherent flammability, and brittleness of EP were completely overcome through the successful application of POM(Mo)-POSS(ibu-Li) supramolecular nanosheets.

Ultra-high Performance Thermochromic Polymers via a Solid-solid Phase Transition Mechanism and Their Applications

Thermochromic materials are substances that change color in response to temperature variations. Today, sustainability concerns are the main drivers of thermochromic research, with smart, energy-efficient windows being one of the primary applications. While vanadium oxides and leuco dyes are traditionally the main thermochromic materials, hydrogels operating based on change of solvation have risen as some of the most promising materials due to their high optical transparency and good solar modulating abilities. In this work, a distinct mechanism for thermochromism arising from the crystalline solid to amorphous solid polymer transition, with a corresponding transition from an opaque state to a transparent state is disclosed. Both ultra-high optical transparency (Tlum up to 99%) and ultra-high solar modulation (ΔTsolar up to 87%) are observed. The transition temperature is tunable from 11 to 61 °C by tuning the polymer structure. When incorporated into applications such as greenhouse materials and thermoelectric devices, significant performance enhancement is observed, due to the thermochromic material functioning as a thermal valve, speeding up solar heat absorbance while inhibiting the cooling process via its phase transition.

Crosslinking Vinyl-Addition Polynorbornenes via Difunctional Diazirines to Generate Low Dielectric-Constant and Low Dielectric-Loss Thermosets

Thermosets having low dielectric constant (Dk < 3) and low dielectric dissipation factor (Df < 0.003), high glass transition temperature (Tg > 150 °C), and good adhesion to copper are desirable for the low loss layers of the copper clad laminates (CCL) in next generation printed circuit boards. Three different difunctional diazirines are evaluated for both thermal and photochemical crosslinking of a high Tg vinyl-addition polynorbornene resin: poly(5-hexyl-1-norbornene) (poly(HNB)). The substrate polymer, crosslinked by the carbenes generated from the activated diazirines, forms thermosets with Dk < 2.3 and Df < 0.001 at 10 GHz depending on the identity of the diazirine and the loading. The Dk and Df values for one composition are stable for 1600 h at 125 °C in air and for 1400 h at 85 °C and 85% relative humidity, suggesting good long-term reliability of this thermoset. Adhesion of poly(HNB) to copper can be enhanced by priming the copper surface with a diazirine prior to high temperature lamination; peel strength values of greater than 7.5 N cm-1 are achieved. Negative-tone photopatterning of poly(HNB) with diazirines upon exposure to 365 nm light is demonstrated.

Advances in Nonreactive Polymer Compatibilizers for Commodity Polyolefin Blends

Recycling mixed polyolefin plastics is a significant challenge due to the limitations in sorting and degraded mechanical properties of blends. Nonreactive compatibilization by adding a small amount of polymeric additive is a widespread approach to restoring the performance and value of recycled plastics. Over the past several decades, synthetic advances have enabled access to low-cost copolymers and precision architectures for deepening the understanding of compatibilization mechanisms in semicrystalline polyolefins. This review covers the design parameters of a polymeric compatibilizer, the testing of blends, the synthetic methods of producing economically viable additives, and surveys the literature of blends of compatibilized HDPE, LLDPE, LDPE, and iPP. From this, readers should gain a comprehension of the polymer mechanics, synthesis, and macromolecular engineering of processable polyolefin blends, along with the field's future directions.

Temperature- and Rate-Dependent Fracture in Disulfide Vitrimers

The fracture behaviors of disulfide vitrimers are highly rate-dependent. Our investigation revealed that the temperature-dependent fracture behaviors of disulfide vitrimers cannot be entirely explained by a simple time-temperature superposition model. This Letter explores the impact of the dynamic nature of molecular defects on the temperature- and rate-dependent fracture behaviors of disulfide vitrimers. Considering that the high cross-linking density remains constant during the associated bond exchange reaction, we identify loop defects in the network as the primary dynamic defects. By employing small amplitude oscillatory shear, we measured the loop defect fraction in EPS25 disulfide vitrimers at varied temperatures, revealing an increased presence of loop defects at elevated temperatures. Furthermore, our findings indicate that the temperature-dependent fracture behaviors are attributed to the temperature-dependent number of loop defects in disulfide vitrimers.

Closed-Loop Recycling of Mixed Plastics of Polyester and CO2-Based Polycarbonate to a Single Monomer

Physical blending is an effective strategy for tailoring polymeric materials to specific application requirements. However, physically blended mixed plastics waste adds additional barriers in mechanical or chemical recycling. This difficulty arises from the intricate requirement for meticulous sorting and separation of the various polymers in the inherent incompatibility of mixed polymers during recycling. To overcome this impediment, this work furthers the emerging single-monomer - multiple-materials approach through the design of a bifunctional monomer that can not only orthogonally polymerize into two different types of polymers - specifically lactone-based polyester and CO2-based polycarbonate - but the resultant polymers and their mixture can also be depolymerized back to the single, original monomer when facilitated by catalysis. Specifically, the lactone/epoxide hybrid bifunctional monomer (BiLO) undergoes ring-opening polymerization through the lactone manifold to produce polyester, PE(BiLO), and is also applied to ring-opening copolymerization with CO2, via the epoxide manifold, to yield polycarbonate, PC(BiLO). Remarkably, a one-pot recycling process of a BiLO-derived PE/PC blend back to the constituent monomer BiLO in >99 % selectivity was achieved with a superbase catalyst at 150 °C, thereby effectively obviating the requirement for sorting and separation typically required for recycling of mixed polymers.

Synergistic Dual-Cure Reactions for the Fabrication of Thermosets by Chemical Heating

Large composite structures, such as those used in wind energy applications, rely on the bulk polymerization of thermosets on an impressively large scale. To accomplish this, traditional thermoset polymerizations require both elevated temperatures (>100 °C) and extended cure durations (>5 h) for complete conversion, necessitating the use of oversize ovens or heated molds. In turn, these requirements lead to energy-intensive polymerizations, incurring high manufacturing costs and process emissions. In this study, we develop thermoset polymerizations that can be initiated at room temperature through a transformative "chemical heating" concept, in which the exothermic energy of a secondary reaction is used to facilitate the heating of a primary thermoset polymerization. By leveraging a redox-initiated methacrylate free radical polymerization as a source of exothermic chemical energy, we can achieve peak reaction temperatures >140 °C to initiate the polymerization of epoxy-anhydride thermosets without external heating. Furthermore, by employing Trojan horse methacrylate monomers to induce mixing between methacrylate and epoxy-anhydride domains, we achieve the synthesis of homogeneous hybrid polymeric materials with competitive thermomechanical properties and tunability. Herein, we establish a proof-of-concept for our innovative chemical heating method and advocate for its industrial integration for more energy-efficient and streamlined manufacturing of wind blades and large composite parts more broadly.

Lifecycle Management for Sustainable Plastics: Recent Progress from Synthesis, Processing to Upcycling

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.

Efficient and Robust Dynamic Crosslinking for Compatibilizing Immiscible Mixed Plastics through In Situ Generated Singlet Nitrenes

Creating a sustainable economy for plastics demands the exploration of new strategies for efficient management of mixed plastic waste. The inherent incompatibility of different plastics poses a major challenge in plastic mechanical recycling, resulting in phase-separated materials with inferior mechanical properties. Here, this study presents a robust and efficient dynamic crosslinking chemistry that effectively compatibilizes mixed plastics. Composed of aromatic sulfonyl azides, the dynamic crosslinker shows high thermal stability and generates singlet nitrene species in situ during solvent-free melt-extrusion, effectively promoting C─H insertion across diverse plastics. This new method demonstrates successful compatibilization of binary polymer blends and model mixed plastics, enhancing mechanical performance and improving phase morphology. It holds promise for managing mixed plastic waste, supporting a more sustainable lifecycle for plastics.

Stapler Strategies for Upcycling Mixed Plastics

Mechanical recycling is one of the simplest and most economical strategies to address ever-increasing plastic pollution, but it cannot be applied to immiscible mixed plastics and suffers from property deterioration after each cycle. By combining the amphiphilic block copolymer strategy and reactive compatibilization strategy, we designed a series of stapler strategies for compatibilizing/upcycling mixed plastics. First, various functionalized graft copolymers were accessed via different synthetic routes. Subsequently, the addition of a very small amount of stapler molecules induced a synergistic effect with the graft copolymers that improved the compatibility and mechanical properties of mixed plastics. These strategies were highly effective for various binary/ternary plastic systems and can be directly applied to postconsumer waste plastics, which can increase the toughness of mixed postconsumer waste plastics by 162 times. Most importantly, it also effectively improved the impact resistance, adhesion performance, and three-dimensional (3D) printing performance of mixed plastics, and permitted the recycling of plastic blends 20 times with minimal degradation in their mechanical properties.

Hydroxyl carboxylate anion catalyzed depolymerization of biopolyesters and transformation to chemicals

Upcycling biopolyesters (e.g., polyglycolic acid, PGA) into chemicals is an interesting and challenging topic. Herein, we report a novel protocol to upgrade biopolyesters derived from hydroxyl carboxylic acids over ionic liquids with a hydroxyl carboxylate anion (e.g., glycolate, lactate) into various chemicals under metal-free conditions. It is found that as hydrogen-bond donors and acceptors, hydroxyl carboxylate anions can readily activate the ester group via hydrogen bonding and decompose biopolyesters via autocatalyzed-transesterification to form hydroxyl carboxylate anion-based intermediates. These intermediates can react with various nucleophiles (e.g. H2O, methanol, amines and hydrazine) to access the corresponding acids, esters and amides under mild conditions (e.g., 40 °C). For example, 1-ethyl-3-methylimidazolium glycolate can achieve complete transformation of PGA into various chemicals such as glycolic acid, alkyl glycolates, 2-hydroxy amides, 2-(hydroxymethyl)benzimidazole, and 1,3-benzothiazol-2-ylmethanol in excellent yields via hydrolysis, alcoholysis and aminolysis, respectively. This protocol is simple, green, and highly efficient, which opens a novel way to upcycle biopolyesters to useful chemicals.

New Advances in Covalent Network Polymers via Dynamic Covalent Chemistry

Covalent network polymers, as materials composed of atoms interconnected by covalent bonds in a continuous network, are known for their thermal and chemical stability. Over the past two decades, these materials have undergone significant transformations, gaining properties such as malleability, environmental responsiveness, recyclability, crystallinity, and customizable porosity, enabled by the development and integration of dynamic covalent chemistry (DCvC). In this review, we explore the innovative realm of covalent network polymers by focusing on the recent advances achieved through the application of DCvC. We start by examining the history and fundamental principles of DCvC, detailing its inception and core concepts and noting its key role in reversible covalent bond formation. Then the reprocessability of covalent network polymers enabled by DCvC is thoroughly discussed, starting from the significant milestones that marked the evolution of these polymers and progressing to their current trends and applications. The influence of DCvC on the crystallinity of covalent network polymers is then reviewed, covering their bond diversity, synthesis techniques, and functionalities. In the concluding section, we address the current challenges faced in the field of covalent network polymers and speculates on potential future directions.

Carbene-Mediated Polymer Modification Using Diazo Compounds under Photo or Thermal Activation Conditions

Based on the characteristics of commodity polymers in large quantities and low costs, modification of existing commodity polymers emerges as the most effective approach for exploring novel materials. Nevertheless, conventional modification methods typically involve high-energy processes (e.g., high temperature, high-energy radiation), which may lead to irreversible detrimental effects on the polymers, contradicting the desired performance enhancement through modification. In this work, we propose a carbene-mediated postpolymerization modification (PPM) strategy utilizing diazo compounds. Under photochemical or thermal activation conditions, insertion of the C-H bond can be achieved without compromising the performance of polymers. These diazo compounds can be easily synthesized in just two steps and applied to all C-H-containing polymers. This practical and effective modification strategy offers new opportunities and possibilities for enhancing the value and expanding the applications of polymers.

Ligand Dissociation of Metal-Complex Photocatalysts toward pH-Photomanipulation in Dynamic Covalent Hydrogels for Printing Reprocessable and Recyclable Devices

Dynamic covalent hydrogels are gaining attention for their potential in smart materials, soft devices, electronics, and more thanks to their impressive mechanical properties, biomimetic structures, and dynamic behavior. However, a significant challenge lies in designing precise and efficient dynamic photochemistry for their preparation, allowing for complex structures and control over the dynamic process. Herein, we propose a general and straightforward orthogonal dynamic covalent photochemistry strategy for preparing high-performance printable dynamic covalent hydrogels, thereby broadening their advanced applications. This photochemical strategy uses a bifunctional photocatalyst to initiate radical polymerization and release ligands through a rapid light-mediated dissociation mechanism. This process leads to a controlled increase in system pH from mildly acidic to alkaline conditions within one hundred seconds, which in turn triggers the pH-sensitive model reactions of boronic acid/diol complexation and Knoevenagel condensation. The orthogonal photochemistry enables the formation of interpenetrated and conjoined networks, significantly enhancing the mechanical properties of the hydrogels. The reversible bonds formed during the process, i.e., boronic ester and unsaturated ketone bonds, confer excellent self-healing, reprocessable, and recyclable properties on the hydrogels through photochemical pH variations. Furthermore, this rapid, controlled fabrication process and dynamic behavior are highly compatible with printing techniques, enabling the design of adaptive and recyclable sensors with different structures. These advancements are promising for various material science, medicine, and engineering applications.

Recent Progresses and Challenges in Upcycling of Plastics through Selective Catalytic Oxidation

Chemical upcycling of plastics provides an important direction for solving the challenging issues of plastic pollution and mitigating the wastage of carbon resources. Among them, catalytic oxidative cracking of plastics to produce high-value chemicals, such as catalytic oxidation of polyethylene (PE) to produce fatty dicarboxylic acids, catalytic oxidation of polystyrene (PS) to produce benzoic acid, and catalytic oxidation of polyethylene terephthalate (PET) to produce terephthalic acid under mild conditions has attracted increasing attention, and some exciting progress has been made recently. In this article, we will review recent progresses on the catalytic oxidation upcycling of plastics and provide our understanding on the current challenges in catalytic oxidation upcycling of plastics.

A Vitrimer Acts as a Compatibilizer for Polyethylene and Polypropylene Blends

Polymer compatibilization plays a critical role in achieving polymer blends with favorable mechanical properties and enabling efficient recycling of mixed plastic wastes. Nonetheless, traditional compatibilization methods often require tailored designs based on the specific chemical compositions of the blends. In this study, we propose a new approach for compatibilizing polymer blends using a dynamically crosslinked polymer network, known as vitrimers. By adding a relatively small amount (1-5 w/w%) of a vitrimer made of siloxane-crosslinked high-density polyethylene (HDPE), we successfully compatibilized unmodified HDPE and isotactic polypropylene (iPP). The vitrimer-compatibilized blend exhibited enhanced elongation at break (120 %) and smaller iPP domain sizes (0.4 μm) compared to the control blend (22 % elongation at break, 0.9 μm iPP droplet size). Moreover, the vitrimer-compatibilized blend showed significantly improved microphase stability during annealing at 180 °C. This straightforward method shows promise for applications across various polymer blend systems.

Catalyst-Free α-Acetyl Cinnamate/Acetoacetate Exchange to Enable High Creep-Resistant Vitrimers

Vitrimers represent an emerging class of polymeric materials that combine the desirable characteristics of both thermoplastics and thermosets achieved through the design of dynamic covalent bonds within the polymer networks. However, these materials are prone to creep due to the inherent instability of dynamic covalent bonds. Consequently, there are pressing demands for the development of robust and stable dynamic covalent chemistries. Here, we report a catalyst-free α-acetyl cinnamate/acetoacetate (α-AC/A) exchange reaction to develop vitrimers with remarkable creep resistance. Small-molecule model studies revealed that the α-AC/A exchange occurred at temperatures above 140 °C in bulk, whereas at 120 °C, this reaction was absent. For demonstration in the case of polymers, copolymers derived from common vinyl monomers were crosslinked with terephthalaldehyde to produce α-AC/A vitrimers with tunable thermal and mechanical performance. All resulting α-AC/A vitrimers exhibited high stability, especially in terms of creep resistance at 120 °C, while retaining commendable reprocessability when subjected to high temperatures. This work showcases the α-AC/A exchange reaction as a novel and robust dynamic covalent chemistry capable of imparting both reprocessability and high stability to cross-linked networks.

Molecular Simulation of Covalent Adaptable Networks and Vitrimers: A Review

Covalent adaptable networks and vitrimers are novel polymers with dynamic reversible bond exchange reactions for crosslinks, enabling them to modulate their properties between those of thermoplastics and thermosets. They have been gathering interest as materials for their recycling and self-healing properties. In this review, we discuss different molecular simulation efforts that have been used over the last decade to investigate and understand the nanoscale and molecular behaviors of covalent adaptable networks and vitrimers. In particular, molecular dynamics, Monte Carlo, and a hybrid of molecular dynamics and Monte Carlo approaches have been used to model the dynamic bond exchange reaction, which is the main mechanism of interest since it controls both the mechanical and rheological behaviors. The molecular simulation techniques presented yield sufficient results to investigate the structure and dynamics as well as the mechanical and rheological responses of such dynamic networks. The benefits of each method have been highlighted. The use of other tools such as theoretical models and machine learning has been included. We noticed, amongst the most prominent results, that stress relaxes as the bond exchange reaction happens, and that at temperatures higher than the glass transition temperature, the self-healing properties are better since more bond BERs are observed. The lifetime of dynamic covalent crosslinks follows, at moderate to high temperatures, an Arrhenius-like temperature dependence. We note the modeling of certain properties like the melt viscosity with glass transition temperature and the topology freezing transition temperature according to a behavior ruled by either the Williams-Landel-Ferry equation or the Arrhenius equation. Discrepancies between the behavior in dissociative and associative covalent adaptable networks are discussed. We conclude by stating which material parameters and atomistic factors, at the nanoscale, have not yet been taken into account and are lacking in the current literature.

Compatibilization of Immiscible Polypropylene/Poly(methyl methacrylate) Blends by Silica Particles with Janus and Random Component-Selective Grafts

Introducing component-selective polymer chains onto the surface of a particle is an effective approach to improve the compatibilization efficiency of a particle-based compatibilizer. In this study, two particles with different kinds of component-selective polymer chains that have the same length and similar density but different graft locations were synthesized and their compatibilization effects were comparatively investigated. It was found that compared with the particle with homogeneous PMMA and PP grafts (R-P), the particle with a hemisphere of poly(methyl methacrylate) (PMMA) grafts and other hemisphere of polypropylene (PP) chains (J-P) showed a better compatibilization effect under equal loadings, although both particles exhibited high efficiency. The better compatibilization effect of particles with Janus grafts may be attributed to the stronger entanglements between grafted polymer chains and selective individual components. This work suggests that optimizing the graft location of a particle is an effective strategy for improving its compatibilization efficiency and helpful for the design of advanced particle compatibilizers.

Recyclable, Malleable, and Strong Thermosets Enabled by Knoevenagel Adducts

Plastic recycling is critical for waste management and achieving a circular economy, but it entails difficult trade-offs between performance and recyclability. Here, we report a thermoset, poly(α-cyanocinnamate) (PCC), synthesized using Knoevenagel condensation between terephthalaldehyde (TPA) and a triarm cyanoacetate star, that tackles this difficulty by harnessing its intrinsically conjugated and dynamic chemical characteristics. PCCs exhibit extraordinary thermal and mechanical properties with a typical Tg of ∼178 °C, Young's modulus of 3.8 GPa, and tensile strength of 102 MPa, along with remarkable flexibility and dimensional and chemical stabilities. Furthermore, end-of-life PCCs can be selectively degraded and partially recycled back into one starting monomer TPA for a new production cycle or reprocessed through dynamic exchange aided by cyanoacetate chain-ends. This study lays the scientific groundwork for the design of robust and recyclable thermosets, with transformative potential in plastic engineering.

Recyclable and (Bio)degradable Polyesters in a Circular Plastics Economy

Polyesters carrying polar main-chain ester linkages exhibit distinct material properties for diverse applications and thus play an important role in today's plastics economy. It is anticipated that they will play an even greater role in tomorrow's circular plastics economy that focuses on sustainability, thanks to the abundant availability of their biosourced building blocks and the presence of the main-chain ester bonds that can be chemically or biologically cleaved on demand by multiple methods and thus bring about more desired end-of-life plastic waste management options. Because of this potential and promise, there have been intense research activities directed at addressing recycling, upcycling or biodegradation of existing legacy polyesters, designing their biorenewable alternatives, and redesigning future polyesters with intrinsic chemical recyclability and tailored performance that can rival today's commodity plastics that are either petroleum based and/or hard to recycle. This review captures these exciting recent developments and outlines future challenges and opportunities. Case studies on the legacy polyesters, poly(lactic acid), poly(3-hydroxyalkanoate)s, poly(ethylene terephthalate), poly(butylene succinate), and poly(butylene-adipate terephthalate), are presented, and emerging chemically recyclable polyesters are comprehensively reviewed.

Dynamic Interfaces in Self-Healable Polymers

It is well-established that interfaces play critical roles in biological and synthetic processes. Aside from significant practical applications, the most accessible and measurable quantity is interfacial tension, which represents a measure of the energy required to create or rejoin two surfaces. Owing to the fact that interfacial processes are critical in polymeric materials, this review outlines recent advances in dynamic interfacial processes involving physics and chemistry targeting self-healing. Entropic interfacial energies stored during damage participate in the recovery, and self-healing depends upon copolymer composition and monomer sequence, monomer molar ratios, molecular weight, and polymer dispersity. These properties ultimately impact chain flexibility, shape-memory recovery, and interfacial interactions. Self-healing is a localized process with global implications on mechanical and other properties. Selected examples driven by interfacial flow and shape memory effects are discussed in the context of covalent and supramolecular rebonding targeting self-healable materials development.

Dynamic Chemistry Toolbox for Advanced Sustainable Materials

Developing dynamic chemistry for polymeric materials offers chemical solutions to solve key problems associated with current plastics. Mechanical performance and dynamic function are equally important in material design because the former determines the application scope and the latter enables chemical recycling and hence sustainability. However, it is a long-term challenge to balance the subtle trade-off between mechanical robustness and dynamic properties in a single material. The rise of dynamic chemistry, including supramolecular and dynamic covalent chemistry, provides many opportunities and versatile molecular tools for designing constitutionally dynamic materials that can adapt, repair, and recycle. Facing the growing social need for developing advanced sustainable materials without compromising properties, recent progress showing how the toolbox of dynamic chemistry can be explored to enable high-performance sustainable materials by molecular engineering strategies is discussed here. The state of the art and recent milestones are summarized and discussed, followed by an outlook toward future opportunities and challenges present in this field.

MatGPT: A Vane of Materials Informatics from Past, Present, to Future

Combining materials science, artificial intelligence (AI), physical chemistry, and other disciplines, materials informatics is continuously accelerating the vigorous development of new materials. The emergence of "GPT (Generative Pre-trained Transformer) AI" shows that the scientific research field has entered the era of intelligent civilization with "data" as the basic factor and "algorithm + computing power" as the core productivity. The continuous innovation of AI will impact the cognitive laws and scientific methods, and reconstruct the knowledge and wisdom system. This leads to think more about materials informatics. Here, a comprehensive discussion of AI models and materials infrastructures is provided, and the advances in the discovery and design of new materials are reviewed. With the rise of new research paradigms triggered by "AI for Science", the vane of materials informatics: "MatGPT", is proposed and the technical path planning from the aspects of data, descriptors, generative models, pretraining models, directed design models, collaborative training, experimental robots, as well as the efforts and preparations needed to develop a new generation of materials informatics, is carried out. Finally, the challenges and constraints faced by materials informatics are discussed, in order to achieve a more digital, intelligent, and automated construction of materials informatics with the joint efforts of more interdisciplinary scientists.

Upcycling Polyolefin Blends into High-Performance Materials by Exploiting Azidotriazine Chemistry Using Reactive Extrusion

The revalorization of incompatible polymer blends is a key obstacle in realizing a circular economy in the plastics industry. Polyolefin waste is particularly challenging because it is difficult to sort into its constituent components. Untreated blends of polyethylene and polypropylene typically exhibit poor mechanical properties that are suitable only for low-value applications. Herein, we disclose a simple azidotriazine-based grafting agent that enables polyolefin blends to be directly upcycled into high-performance materials by using reactive extrusion at industrially relevant processing temperatures. Based on a series of model experiments, the azidotriazine thermally decomposes to form a triplet nitrene species, which subsequently undergoes a complex mixture of grafting, oligomerization, and cross-linking reactions; strikingly, the oligomerization and cross-linking reactions proceed through the formation of nitrogen-nitrogen bonds. When applied to polyolefin blends during reactive extrusion, this combination of reactions leads to the generation of amorphous, phase-separated nanostructures that tend to exist at polymer-polymer interfaces. These nanostructures act as multivalent cross-linkers that reinforce the resulting material, leading to dramatically improved ductility compared with the untreated blends, along with high dimensional stability at high temperatures and excellent mechanical recyclability. We propose that this unique behavior is derived from the thermomechanically activated reversibility of the nitrogen-nitrogen bonds that make up the cross-linking structures. Finally, the scope of this chemistry is demonstrated by applying it to ternary polyolefin blends as well as postconsumer polyolefin feedstocks.

The Effect of Coupling Agents and Graphene on the Mechanical Properties of Film-Based Post-Consumer Recycled Plastic

This study aims to improve the mechanical properties of post-consumer recycled (PCR) plastic composed primarily of polypropylene (PP) and polyethylene (PE), which generally exhibit poor miscibility, by applying coupling agents and graphene. Here, we compare a commercially available coupling agent with a directly synthesized maleic anhydride (MA) coupling agent. When applied to a 5:5 blend of recycled PP and PE, an optimum tensile strength was achieved at a 3 wt% coupling agent concentration, with the MA coupling agent outperforming the commercial one. Characterization through Fourier transform infrared spectroscopy (FT-IR) and thermogravimetry analysis (TGA) revealed a PP:PE ratio of approximately 3:7 in the PCR plastics, with 4.86% heterogeneous materials present. Applying 3 wt% of the commercial and MA coupling agents to the PCR plastics resulted in a significant 53.9% increase in the tensile strength, reaching 11.25 MPa, and a remarkable 421.54% increase in the melt flow index (MFI), reaching 25.66 g/10 min. Furthermore, incorporating 5 wt% graphene led to a notable 64.84% increase in the tensile strength. In addition, the application of MA coupling agents and graphene improved the thermal stability of the PCR plastics. These findings show significant promise for addressing environmental concerns associated with plastic waste by facilitating the recycling of PCR plastics into new products. The utilization of coupling agents and graphene offers a viable approach to enhance the mechanical properties of PCR plastics, paving the way for sustainable and environmentally friendly solutions.

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.

Polymer Multi-Block and Multi-Block+ Strategies for the Upcycling of Mixed Polyolefins and Other Plastics

Due to a continued rise in the production and use of plastic products, their end-of-life pollution has become a pressing global issue. One of the biggest challenges in plastics recycling is the separation of different polymers. Multi-block copolymers (MBCPs) represent an efficient strategy for the upcycling of mixed plastics via induced compatibilization, but this approach is limited by difficulties associated with synthesis and structural modification. In this contribution, several synthetic strategies are explored to prepare MBCPs with tunable microstructures, which were then used as compatibilizer additives to upcycle mixtures of polyolefins with other plastics. A multi-block+ strategy based on a reactive telechelic block copolymer platform was introduced, which enabled block extension during the in situ melt blending of mixed plastics, leading to better compatibilizing properties as well as better 3D printing capability. This strategy was also applicable to more complex ternary plastic blends. The polymer multi-block strategy enabled by versatile MBCPs synthesis and the multi-block+ strategy enabled by in situ block extension show exciting opportunities for the upcycling of mixed plastics.

Closed-Loop Recyclable Silica-Based Nanocomposites with Multifunctional Properties and Versatile Processability

Most plastics originate from limited petroleum reserves and cannot be effectively recycled at the end of their life cycle, making them a significant threat to the environment and human health. Closed-loop chemical recycling, by depolymerizing plastics into monomers that can be repolymerized, offers a promising solution for recycling otherwise wasted plastics. However, most current chemically recyclable polymers may only be prepared at the gram scale, and their depolymerization typically requires harsh conditions and high energy consumption. Herein, it reports less petroleum-dependent closed-loop recyclable silica-based nanocomposites that can be prepared on a large scale and have a fully reversible polymerization/depolymerization capability at room temperature, based on catalysis of free aminopropyl groups with the assistance of diethylamine or ethylenediamine. The nanocomposites show glass-like hardness yet plastic-like light weight and toughness, exhibiting the highest specific mechanical strength superior even to common materials such as poly(methyl methacrylate), glass, and ZrO2 ceramic, as well as demonstrating multifunctionality such as anti-fouling, low thermal conductivity, and flame retardancy. Meanwhile, these nanocomposites can be easily processed by various plastic-like scalable manufacturing methods, such as compression molding and 3D printing. These nanocomposites are expected to provide an alternative to petroleum-based plastics and contribute to a closed-loop materials economy.

Covalent Adaptable Networks through Dynamic N,S-Acetal Chemistry: Toward Recyclable CO2-Based Thermosets

Finding new chemistry platforms for easily recyclable polymers has become a key challenge to face environmental concerns and the growing plastics demand. Here, we report a dynamic chemistry between CO2-sourced alkylidene oxazolidones and thiols, delivering circular non-isocyanate polyurethane networks embedding N,S-acetal bonds. The production of oxazolidone monomers from CO2 is facile and scalable starting from cheap reagents. Their copolymerization with a polythiol occurs under mild conditions in the presence of a catalytic amount of acid to furnish polymer networks. The polymer structure is easily tuned by virtue of monomer design, translating into a wide panel of mechanical properties similar to commodity plastics, ranging from PDMS-like elastomers [with Young's modulus (E) of 2.9 MPa and elongation at break (εbreak) of 159%] to polystyrene-like rigid plastics (with E = 2400 MPa, εbreak = 3%). The highly dissociative nature of the N,S-acetal bonds is demonstrated and exploited to offer three different recycling scenarios to the thermosets: (1) mechanical recycling by compression molding, extrusion, or injection molding─with multiple recycling (at least 10 times) without any material property deterioration, (2) chemical recycling through depolymerization, followed by repolymerization, also applicable to composites, and (3) upcycling of two different oxazolidone-based thermosets into a single one with distinct properties. This work highlights a new facile and scalable chemical platform for designing highly dynamic polymer networks containing elusive oxazolidone motifs. The versatility of this chemistry shows great potential for the preparation of materials (including composites) of tuneable structures and properties, with multiple end-of-life scenarios.

Does the Varying Reactivity in the Transient Polymer Network through Dynamic Exchange Regulate the Closed-Loop Circularity in Polyolefin Vitrimers?

According to current projections, of the 400 mega tons of plastic produced globally, 70% is waste and of that only 16% is recycled and the rest is incinerated. This is estimated to contribute to ca. 16% of the net carbon emission by 2050. Such a massive amount of unmanaged plastic waste and the associated huge carbon footprint sets a significant challenge to tackle in the coming decades. To achieve net-zero carbon emission, closed-loop circular economy in plastics is crucial but collection, sorting and processing the postconsumer recycled (PCR) plastics poses humongous challenge in achieving this circularity, unless an effective strategy is designed. In a first of its kind, a designer biobased molecule was synthesized (here maleated castor oil, mCO) that is steric and thermally stable and forms in situ "homo-cross-linking" in the melt post grafting onto PCR-PP. This designer molecule, besides offering a transient network, helps bridge the fragmented PP chains which is usually not amenable from the traditional grafting (like maleic anhydride), thereby addressing a long-standing challenge of retaining the properties post grafting due to chain scission in the melt. The resulting maleated (m) PCR-PP now offers abundant functionality which helped us design single and dual covalent adaptable network (CANs) and evaluate their consequences on the structure-property correlation. The PCR-PP Vitrimers demonstrate a distinct rubbery plateau in the melt and reprocessability with >90% recovery in mechanical properties even after the fifth sequence of recycling. We propose here for the first time how the varying reactivity (single or dual) in the transient polymer network, through dynamic exchange, regulates the closed-loop circularity in PP Vitrimers. Our results begin to suggest that the varying reactivity should be taken into account as an additional design parameter, as it influences both the stress relaxation rates and the flow activation energy. We now understand that the topology reconfiguration is strongly dependent on this varying reactivity, which also controls the overall crystalline morphology and the structural properties in the Vitrimers. This study, in addition to opening new avenues for recycling PP, will help guide researchers working in this field from both academia and industry.

Thermal/Blue Light Induced Cross-Linking of Acrylic Coatings with Diazo Compounds

The thermal curing of industrial coatings (e.g., car painting and metal coil coatings) is accompanied by a substantial energy consumption due to the intrinsically high temperatures required during the curing process. Therefore, the development of new photochemical curing processes-preferably using visible light-is in high demand. This work describes new diazo-based cross-linkers that can be used to photocure acrylic coatings using blue light. This work demonstrates that the structure of the tethered diazo compounds influences the cross-linking efficiency, finding that side reactions are suppressed upon engineering greater molecular flexibility. Importantly, this work shows that these diazo compounds can be employed as either thermal or photochemical cross-linkers, exhibiting identical crosslinking performances. The performance of diazo-cross-linked coatings is evaluated to reveal excellent water resistance and demonstrably similar material properties to UV-cured acrylates. These studies pave the way for further usage of diazo-functionalized cross-linkers in the curing of paints and coatings.

Mixed Plastics Wastes Upcycling with High-Stability Single-Atom Ru Catalyst

Mixed plastic waste treatment has long been a significant challenge due to complex composition and sorting costs. In this study, we have achieved a breakthrough in converting mixed plastic wastes into a single chemical product using our innovative single-atom catalysts for the first time. The single-atom Ru catalyst can convert ∼90% of real mixed plastic wastes into methane products (selectivity >99%). The unique electronic structure of Ru sites regulates the adsorption energy of mixed plastic intermediates, leading to rapid decomposition of mixed plastics and superior cycle stability compared to traditional nanocatalysts. The global warming potential of the entire process was evaluated. Our proposed carbon-reducing process utilizing single-atom catalysts launches a new era of mixed plastic waste valorization.