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All-day passive radiative cooling has recently attracted tremendous interest by reflecting sunlight and radiating heat to the ultracold outer space. While some progress has been made, it still remains big challenge in fabricating highly efficient and low-cost radiative coolers for all-day and all-climates. Herein, we report a hierarchically structured polymethyl methacrylate (PMMA) film with a micropore array combined with random nanopores for highly efficient day- and nighttime passive radiative cooling. This hierarchically porous array PMMA film exhibits sufficiently high solar reflectance (0.95) and superior longwave infrared thermal emittance (0.98) and realizes subambient cooling of ~8.2 °C during the night and ~6.0 °C to ~8.9 °C during midday with an average cooling power of ~85 W/m 2 under solar intensity of ~900 W/m 2 , and promisingly ~5.5 °C even under solar intensity of ~930 W/m 2 and relative humidity of ~64% in hot and moist climate. The micropores and nanopores in the polymer film play crucial roles in enhancing the solar reflectance and thermal emittance. There still remains a big challenge in fabricating highly efficient and low-cost radiative coolers for all-day and all-climates. Here, the authors report a hierarchically structured polymethyl methacrylate film with a micropore array combined with random nanopores for highly efficient day- and nighttime passive radiative cooling.

The vast majority of commodity plastics do not degrade and therefore they permanently pollute the environment. At present, less than 20% of post-consumer plastic waste in developed countries is recycled, predominately for energy recovery or repurposing as lower-value materials by mechanical recycling. Chemical recycling offers an opportunity to revert plastics back to monomers for repolymerization to virgin materials without altering the properties of the material or the economic value of the polymer. For plastic waste that is either cost prohibitive or infeasible to mechanically or chemically recycle, the nascent field of chemical upcycling promises to use chemical or engineering approaches to place plastic waste at the beginning of a new value chain. Here state-of-the-art methods are highlighted for upcycling plastic waste into value-added performance materials, fine chemicals and specialty polymers. By identifying common conceptual approaches, we critically discuss how the advantages and challenges of each approach contribute to the goal of realizing a sustainable plastics economy. Methods for the transformation of plastics into materials with value, known as plastic waste upcycling, are outlined, and their advantages and challenges in terms of a sustainable plastics economy are discussed.

Covalent organic frameworks (COFs) are distinguished from other organic polymers by their crystallinity 1 – 3 , but it remains challenging to obtain robust, highly crystalline COFs because the framework-forming reactions are poorly reversible 4 , 5 . More reversible chemistry can improve crystallinity 6 – 9 , but this typically yields COFs with poor physicochemical stability and limited application scope 5 . Here we report a general and scalable protocol to prepare robust, highly crystalline imine COFs, based on an unexpected framework reconstruction. In contrast to standard approaches in which monomers are initially randomly aligned, our method involves the pre-organization of monomers using a reversible and removable covalent tether, followed by confined polymerization. This reconstruction route produces reconstructed COFs with greatly enhanced crystallinity and much higher porosity by means of a simple vacuum-free synthetic procedure. The increased crystallinity in the reconstructed COFs improves charge carrier transport, leading to sacrificial photocatalytic hydrogen evolution rates of up to 27.98 mmol h −1  g −1 . This nanoconfinement-assisted reconstruction strategy is a step towards programming function in organic materials through atomistic structural control. A protocol in which monomers are pre-organized using a reversible and removable urea linkage enables the production of covalent organic frameworks with higher crystallinity and porosity than those produced using standard approaches with randomly aligned monomers.

Conducting polymers (CPs) with high conductivity and solution processability have made great advances since the pioneering work on doped polyacetylene 1 – 3 , thus creating the new field of ‘organic synthetic metals, 4 . Various high-performance CPs have been realized, which enable the applications of several organic electronic devices 5 , 6 . Nevertheless, most CPs exhibit hole-dominant (p-type) transport behaviour 7 , 8 , whereas the development of n-type analogues lags far behind and only a few exhibit metallic state, typically limited by low doping efficiency and ambient instability. Here we present a facilely synthesized highly conductive n-type polymer poly(benzodifurandione) (PBFDO). The reaction combines oxidative polymerization and in situ reductive n-doping, greatly increasing the doping efficiency, and a doping level of almost 0.9 charges per repeating unit can be achieved. The resultant polymer exhibits a breakthrough conductivity of more than 2,000 S cm −1 with excellent stability and an unexpected solution processability without extra side chains or surfactants. Furthermore, detailed investigations on PBFDO show coherent charge-transport properties and existence of metallic state. The benchmark performances in electrochemical transistors and thermoelectric generators are further demonstrated, thus paving the way for application of the n-type CPs in organic electronics. A reaction is described combining oxidative polymerization and in situ reductive n-doping to yield poly(benzodifurandione), a facilely synthesized stable n-type conducting polymer with ultrahigh conductivity, with applications in organic electronics.

The additive manufacturing of photopolymer resins by means of vat photopolymerization enables the rapid fabrication of bespoke 3D-printed parts. Advances in methodology have continually improved resolution and manufacturing speed, yet both the process design and resin technology have remained largely consistent since its inception in the 1980s 1 . Liquid resin formulations, which are composed of reactive monomers and/or oligomers containing (meth)acrylates and epoxides, rapidly photopolymerize to create crosslinked polymer networks on exposure to a light stimulus in the presence of a photoinitiator 2 . These resin components are mostly obtained from petroleum feedstocks, although recent progress has been made through the derivatization of renewable biomass 3 – 6 and the introduction of hydrolytically degradable bonds 7 – 9 . However, the resulting materials are still akin to conventional crosslinked rubbers and thermosets, thus limiting the recyclability of printed parts. At present, no existing photopolymer resin can be depolymerized and directly re-used in a circular, closed-loop pathway. Here we describe a photopolymer resin platform derived entirely from renewable lipoates that can be 3D-printed into high-resolution parts, efficiently deconstructed and subsequently reprinted in a circular manner. Previous inefficiencies with methods using internal dynamic covalent bonds 10 – 17 to recycle and reprint 3D-printed photopolymers are resolved by exchanging conventional (meth)acrylates for dynamic cyclic disulfide species in lipoates. The lipoate resin platform is highly modular, whereby the composition and network architecture can be tuned to access printed materials with varied thermal and mechanical properties that are comparable to several commercial acrylic resins. A photopolymer platform derived from renewable lipoates can be 3D-printed into high-resolution parts, which possess properties comparable to some commercial acrylic resins, and then recycled to produce a re-printable resin.

A core feature of covalent organic frameworks (COFs) is crystallinity, but current crystallization processes rely substantially on trial and error, chemical intuition and large-scale screening, which typically require harsh conditions and low levels of supersaturation, hampering the controlled synthesis of single-crystal COFs, particularly on large scales. Here we report a strategy to produce single-crystal imine-linked COFs in aqueous solutions under ambient conditions using amphiphilic amino-acid derivatives with long hydrophobic chains. We propose that these amphiphilic molecules self-assemble into micelles that serve as dynamic barriers to separate monomers in aqueous solution (nodes) and hydrophobic compartments of the micelles (linkers), thereby regulating the polymerization and crystallization processes. Disordered polyimines were obtained in the micelle, which were then converted into crystals in a step-by-step fashion. Five different three-dimensional COFs and a two-dimensional COF were obtained as single crystals on the gram scale, with yields of 92% and above.Covalent organic frameworks (COFs) have remained difficult to grow as single crystals. Now, amphiphilic amino-acid derivatives that assemble in micelles in aqueous solutions have been shown to promote the growth of a variety of imine-bridged COFs into single crystals, in a step-by-step fashion, within their hydrophobic compartment.

The properties of polycrystalline materials are often dominated by defects; two-dimensional (2D) crystals can even be divided and disrupted by a line defect 1 – 3 . However, 2D crystals are often required to be processed into films, which are inevitably polycrystalline and contain numerous grain boundaries, and therefore are brittle and fragile, hindering application in flexible electronics, optoelectronics and separation 1 – 4 . Moreover, similar to glass, wood and plastics, they suffer from trade-off effects between mechanical strength and toughness 5 , 6 . Here we report a method to produce highly strong, tough and elastic films of an emerging class of 2D crystals: 2D covalent organic frameworks (COFs) composed of single-crystal domains connected by an interwoven grain boundary on water surface using an aliphatic bi-amine as a sacrificial go-between. Films of two 2D COFs have been demonstrated, which show Young’s moduli and breaking strengths of 56.7 ± 7.4 GPa and 73.4 ± 11.6 GPa, and 82.2 ± 9.1 N m −1 and 29.5 ± 7.2 N m −1 , respectively. We predict that the sacrificial go-between guided synthesis method and the interwoven grain boundary will inspire grain boundary engineering of various polycrystalline materials, endowing them with new properties, enhancing their current applications and paving the way for new applications. A method is reported that produces highly strong, tough and elastic 2D COF films, using a sacrificial go-between, which endows them with new properties, enhances their current applications and paves the way for new applications.

With the rapid development of scanning probe microscopy, it has become possible to study polymerization processes on suitable surfaces at the atomic level and in real space. In the two-dimensional confinement of a surface, polymerization reactions can give rise to the formation of unprecedented polymers with unique structures and properties, not accessible in solution. After a little over one decade since the discovery of covalent on-surface polymerization, we give an overview of the field, analyse the crucial aspects and critically reflect on the status quo. Specifically, we provide some general considerations about fundamental mechanisms as well as kinetics and thermodynamics of on-surface polymerization processes. The important role of the surface is detailed in view of its ability to control polymer formation with regard to structure, dimensionality and composition. Furthermore, examples that allow for locally induced polymerization are highlighted. Finally, we provide an analysis of scientific challenges in the field and outline future prospects.Growing polymers directly on surfaces has emerged as a powerful tool because it can provide a route to otherwise inaccessible structures such as defect-free linear chains, graphene nanoribbons and two-dimensional networks. This Review Article describes general principles and key aspects of this method from the perspectives of surface science and polymer chemistry.

Self-repairable materials strive to emulate curable and resilient biological tissue; however, their performance is currently insufficient for commercialization purposes because mending and toughening are mutually exclusive. Herein, we report a carbonate-type thermoplastic polyurethane elastomer that self-heals at 35 °C and exhibits a tensile strength of 43 MPa; this elastomer is as strong as the soles used in footwear. Distinctively, it has abundant carbonyl groups in soft-segments and is fully amorphous with negligible phase separation due to poor hard-segment stacking. It operates in dual mechano-responsive mode through a reversible disorder-to-order transition of its hydrogen-bonding array; it heals when static and toughens when dynamic. In static mode, non-crystalline hard segments promote the dynamic exchange of disordered carbonyl hydrogen-bonds for self-healing. The amorphous phase forms stiff crystals when stretched through a transition that orders inter-chain hydrogen bonding. The phase and strain fully return to the pre-stressed state after release to repeat the healing process. Self-healing materials strive to emulate curable and resilient biological tissue but their performance is often insufficient for commercial applications because self-healing and toughening are mutually exclusive properties. Here, the authors report a tough and strong carbonate-type thermoplastic polyurethane elastomer that self-heals at ambient temperature.

Thermosets—polymeric materials that adopt a permanent shape upon curing—have a key role in the modern plastics and rubber industries, comprising about 20 per cent of polymeric materials manufactured today, with a worldwide annual production of about 65 million tons 1 , 2 . The high density of crosslinks that gives thermosets their useful properties (for example, chemical and thermal resistance and tensile strength) comes at the expense of degradability and recyclability. Here, using the industrial thermoset polydicyclopentadiene as a model system, we show that when a small number of cleavable bonds are selectively installed within the strands of thermosets using a comonomer additive in otherwise traditional curing workflows, the resulting materials can display the same mechanical properties as the native material, but they can undergo triggered, mild degradation to yield soluble, recyclable products of controlled size and functionality. By contrast, installation of cleavable crosslinks, even at much higher loadings, does not produce degradable materials. These findings reveal that optimization of the cleavable bond location can be used as a design principle to achieve controlled thermoset degradation. Moreover, we introduce a class of recyclable thermosets poised for rapid deployment. A method of endowing thermoset plastics with a degree of recyclability and reprocessability by incorporating cleavable chemical linkages in the strands of the polymer, rather than in the crosslinks, is presented.