Porosity is a rare property for molecular materials but, surprisingly, porous solids built from discrete organic cage molecules have emerged as a versatile functional-materials platform. From modest ...beginnings less than a decade ago, there are now organic cage solids with surface areas that can rival extended metal–organic frameworks. In contrast to network polymers and frameworks, these organic cages are synthesized first and then assembled in the solid state in a separate step. This offers solution-processing options that are not available for insoluble organic and inorganic frameworks. In this Review, we highlight examples of porous organic cages and focus on the unique features that set them apart, such as their molecular solubility, their increased tendency to exhibit polymorphism and the scope for modular co-crystallization.The surface areas of molecular organic cage solids now rival those of metal–organic frameworks. In this Review, the synthesis and structures of various porous organic cages are outlined together with a discussion of the characteristics — such as solubility, polymorphism and modular co-crystallization — that distinguish these cages from their inorganic or hybrid counterparts.
Abstract
Inverse vulcanization, a sustainable platform, can transform sulfur, an industrial by-product, into polymers with broad promising applications such as heavy metal capture, electrochemistry ...and antimicrobials. However, the process usually requires high temperatures (≥159 °C), and the crosslinkers needed to stabilize the sulfur are therefore limited to high-boiling-point monomers only. Here, we report an alternative route for inverse vulcanization—mechanochemical synthesis, with advantages of mild conditions (room temperature), short reaction time (3 h), high atom economy, less H
2
S, and broader monomer range. Successful generation of polymers using crosslinkers ranging from aromatic, aliphatic to volatile, including renewable monomers, demonstrates this method is powerful and versatile. Compared with thermal synthesis, the mechanochemically synthesized products show enhanced mercury capture. The resulting polymers show thermal and light induced recycling. The speed, ease, versatility, safety, and green nature of this process offers a more potential future for inverse vulcanization, and enables further unexpected discoveries.
The discovery of inverse vulcanization has allowed stable polymers to be made from elemental sulfur, an unwanted by-product of the petrochemicals industry. However, further development of both the ...chemistry and applications is handicapped by the restricted choice of cross-linkers and the elevated temperatures required for polymerisation. Here we report the catalysis of inverse vulcanization reactions. This catalytic method is effective for a wide range of crosslinkers reduces the required reaction temperature and reaction time, prevents harmful H
S production, increases yield, improves properties, and allows crosslinkers that would be otherwise unreactive to be used. Thus, inverse vulcanization becomes more widely applicable, efficient, eco-friendly and productive than the previous routes, not only broadening the fundamental chemistry itself, but also opening the door for the industrialization and broad application of these fascinating materials.
Inverse vulcanization is a potential route to the use of the large excesses of elemental sulfur, creating high-sulfur-content polymers with many potential applications. The addition of a metal ...diethyldithiocarbamate catalyst was previously found to bring several benefits to inverse vulcanization, making the process more attractive industrially. Herein is reported the establishment and exploration of a library of catalysts for inverse vulcanization. Three ranges of catalysts and up to 32 compounds and their combinations have been investigated. By trialing these alternative catalysts, several tentative deductions about the mechanism have been made. It has been found that stronger nucleophiles give a greater rate enhancement, but with the tradeoff that harder bases may promote hydrogen sulfide byproduct formation. Monomer binding by the cation may be a crucial mechanistic step, and it is possible that the catalysts act as phase transfer agents between the immiscible sulfur and organic phases. Additionally, the versatility of catalytic inverse vulcanization has been demonstrated with several different comonomer families.
Porous organic cage molecules are fabricated into thin films and molecular‐sieving membranes. Cage molecules are solution cast on various substrates to form amorphous thin films, with the structures ...tuned by tailoring the cage chemistry and processing conditions. For the first time, uniform and pinhole‐free microporous cage thin films are formed and demonstrated as molecular‐sieving membranes for selective gas separation.
Molecular crystals cannot be designed in the same manner as macroscopic objects, because they do not assemble according to simple, intuitive rules. Their structures result from the balance of many ...weak interactions, rather than from the strong and predictable bonding patterns found in metal-organic frameworks and covalent organic frameworks. Hence, design strategies that assume a topology or other structural blueprint will often fail. Here we combine computational crystal structure prediction and property prediction to build energy-structure-function maps that describe the possible structures and properties that are available to a candidate molecule. Using these maps, we identify a highly porous solid, which has the lowest density reported for a molecular crystal so far. Both the structure of the crystal and its physical properties, such as methane storage capacity and guest-molecule selectivity, are predicted using the molecular structure as the only input. More generally, energy-structure-function maps could be used to guide the experimental discovery of materials with any target function that can be calculated from predicted crystal structures, such as electronic structure or mechanical properties.
Inverse vulcanization is a bulk polymerization method for synthesizing high sulfur content polymers from elemental sulfur, a byproduct of the petrochemical industry, with vinylic comonomers. There is ...growing interest in polysulfides as novel antimicrobial agents due to the antimicrobial activity of natural polysulfides found in garlic and onions (Tsao et al. J. Antimicrob. Chemother. 2001, 47, 665–670). Herein, we report the antibacterial properties of several inverse vulcanized polymers against Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa, two common causes of nosocomial infection and pathogens identified by the World Health Organization as priorities for antimicrobial development. High sulfur content polymers were synthesized with different divinyl comonomers and at different sulfur/comonomer ratios, to determine the effect of such variables on the antibacterial properties of the resulting materials. Furthermore, polymers were tested for their potential as antibacterial materials at different temperatures. It was found that the test temperature influenced the antibacterial efficacy of the polymers and could be related to the glass transition temperature of the polymer. These findings provide further understanding of the antibacterial properties of inverse vulcanized polymers and show that such polymers have the potential to be used as antibacterial surfaces.
Inverse vulcanization is a copolymerization of elemental sulfur and alkenes that provides unique materials with high sulfur content (typically ≥50% sulfur by mass). These polymers contain a dynamic ...and reactive polysulfide network that creates many opportunities for processing, assembly, and repair that are not possible with traditional plastics, rubbers and thermosets. In this study, we demonstrate that two surfaces of these sulfur polymers can be chemically joined at room temperature through a phosphine or amine-catalyzed exchange of the S-S bonds in the polymer. When the nucleophile is pyridine or triethylamine, we show that S-S metathesis only occurs at room temperature for a sulfur rank > 2-an important discovery for the design of polymers made by inverse vulcanization. This mechanistic understanding of the S-S metathesis was further supported with small molecule crossover experiments in addition to computational studies. Applications of this chemistry in latent adhesives, additive manufacturing, polymer repair, and recycling are also presented.
Polymers made by inverse vulcanization can be assembled, repaired, and recycled at room temperature through nucleophile-catalyzed S-S metathesis.
A series of porous organic cages is examined for the selective adsorption of sulfur hexafluoride (SF6) over nitrogen. Despite lacking any metal sites, a porous cage, CC3, shows the highest SF6/N2 ...selectivity reported for any material at ambient temperature and pressure, which translates to real separations in a gas breakthrough column. The SF6 uptake of these materials is considerably higher than would be expected from the static pore structures. The location of SF6 within these materials is elucidated by X-ray crystallography, and it is shown that cooperative diffusion and structural rearrangements in these molecular crystals can rationalize their superior SF6/N2 selectivity.
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