Fabrication of High-Performance Polyisocyanurate Aerogels through Cocyclotrimerization of 4,4'-Methylene Diphenyl Diisocyanate and Its Mono-Urethane Derivatives.

Aromatic polyisocyanurate (PIR) aerogels are recognized as advanced porous materials and extensively studied due to their lightweight nature, high porosity, and specific surface area, which attribute to their outstanding thermal insulation properties. The inherent thermal stability of the PIR moieties, combined with great insulating performance, renders PIR aerogels highly suitable for building insulation applications. Nevertheless, materials containing isocyanurate obtained through direct trimerization of aromatic isocyanates exhibit brittleness, resulting in inferior mechanical performance. In order to enhance the processability of the PIR aerogels, we propose a cocyclotrimerization approach involving mixtures of mono- and difunctional aromatic isocyanates. This approach is designed to develop a PIR network with decreased cross-linking density and brittleness. Herein, we developed an array of PIR aerogels from different alkyl chain-modified isocyanate mixtures. The resulting PIR aerogels exhibited high porosity (>89%), a large surface area (∼300 m2/g), superinsulating performance with ultralow thermal conductivity (∼16.8 mW m-1 K-1), notable thermal stability (Td5% ∼ 250 °C), improved mechanical performance, and intrinsic hydrophobicity without the need for postmodification. These high-performance organic aerogels hold significant promise for applications requiring superinsulating materials.

Novel Furfural-Derived Polyaldimines as Latent Hardeners for Polyurethane Adhesives.

Moisture-curing one-component polyurethane systems in adhesive, sealant, and coating applications may show blister formation upon cure. Blisters can be formed when carbon dioxide, generated in the reaction with isocyanate and water, is trapped in the film. This problem can be mitigated by employing latent hardeners such as blocked polyamines, which are activated upon moisture exposure. The hydrolysis of the latent hardener yields the polyamine that quickly reacts with the isocyanate, forming urea linkages, and then chain extends the polymer. The hydrolysis also releases the blocking agent, which can potentially create an unpleasant odor. In this work, a series of di- and trifunctional aldimines were synthesized from commercially available polyamines, biobased hydroxymethyl furfural, and lauroyl chloride. Hydroxymethyl furfural was first esterified with lauroyl chloride and subsequently condensed with the polyamines to form the aldimines. The application of these novel aldimines in a model moisture-curing system allowed the preparation of blister- and odor-free castings. Based on our results, the mechanical performance of the different aldimines in casting and adhesive applications could be related to the polymer network density. This was dependent on the rate of the aldimine hydrolysis reaction to produce the polyamine. In particular, the use of aldimines prepared from polyether amines and 1,5-diamino-2-methylpentane showed excellent adhesive properties.

Closed-Loop Recyclable Poly(imine-acetal)s with Dual-Cleavable Bonds for Primary Building Block Recovery.

Chemical recycling offers a promising solution for the end-of-life treatment of synthetic polymers. However, the efficient recovery of well-defined recycled building blocks continues to be a major challenge, especially for crosslinked thermosets. Here, we developed vanillin-based polymer networks functionalized with dual-cleavable imine and acetal bonds that facilitate chemical recycling to primary building blocks and their convenient separation at the molecular level. A library of crosslinked poly(imine-acetal)s was synthesized by combining the in-bulk synthesized liquid di-vanillin acetal monomer (DVA) with commercially available liquid di- and triamines under solvent-free conditions. These thermosets showed tailor-made thermal and mechanical properties along with outstanding chemical recyclability. Under aqueous acidic conditions, poly(imine-acetal)s selectively and completely disintegrate into small molecules. During the polymer design stage, these compounds were carefully selected to enable facile separation without tedious techniques. As a result, the primary building blocks were isolated in high yields and purity and immediately reused to produce fresh polymers with identical thermomechanical properties. Since our "design for recycling" concept aims at obtaining the primary building blocks rather than monomers after depolymerization, a plethora of possibilities are unlocked to utilize these chemical resources, including closed-loop recycling as portrayed.

Epoxy Thermosets Designed for Chemical Recycling.

Epoxy thermosets constitute a significant portion of high-performance plastics, as they possess excellent thermal and mechanical properties that are applicable in a wide range of industries. Nevertheless, traditional epoxy networks show strict limitations regarding chemical recycling due to their covalently crosslinked structures. Although existing methods provide partial solutions for the recycling of epoxy networks, it is urgent to develop more effective, sustainable, and permanent strategies that will solve the problem at hand. For this purpose, developing smart monomers with functional groups that enable the synthesis and development of fully recyclable polymers is of great importance. This review highlights recent advancements in chemically recyclable epoxy systems and their potential to support a circular plastic economy. Moreover, we evaluate the practicality of polymer syntheses and recycling techniques, and assess the applicability of these networks in industry.

Closed-Loop Recycling of Poly(Imine-Carbonate) Derived from Plastic Waste and Bio-based Resources.

Closed-loop recycling of polymers represents the key technology to convert plastic waste in a sustainable fashion. Efficient chemical recycling and upcycling strategies are thus highly sought-after to establish a circular plastic economy. Here, we present the selective chemical depolymerization of polycarbonate by employing a vanillin derivative as bio-based feedstock. The resulting di-vanillin carbonate monomer was used in combination with various amines to construct a library of reprocessable poly(imine-carbonate)s, which show tailor-made thermal and mechanical properties. These novel poly(imine-carbonate)s exhibit excellent recyclability under acidic and energy-efficient conditions. This allows the recovery of monomers in high yields and purity for immediate reuse, even when mixed with various commodity plastics. This work provides exciting new insights in the design of bio-based circular polymers produced by upcycling of plastic waste with minimal environmental impact.

Cu-tetracatechol metallopolymer catalyst for three component click reactions and ß-borylation of α,ß-unsaturated carbonyl compounds.

Phenol-metal coordination polymers are used in applications such as catalysis, sensing and separation science. In addition, combining eco-friendly conditions with economical and handling advantages of the polymeric catalyst is of interest to the community. Here, we report a simple one pot synthesis of a tetracatechol based ligand and its coordination polymer with copper ions. The Cu polymer showed electrochemical potential with a band gap of 1.01 eV. The BET surface area of the metallopolymer was 91.19 m2 g-1 with 0.14 cm3 g-1 pore volume. The polymer catalyst was used in a one pot three component click reaction and in the borylation of unsaturated carbonyl compounds with a maximum 99% conversion in water and good turnover efficiency even after 4 repetitive catalysis cycles. The polymer catalyst offers several advantages such as high activity, easy handling, scalability, recyclability and cost effectiveness.

Fine-Tuning the Electronic Properties of Azo Chromophore-Incorporated Perylene Bisimide Dyads.

Perylene bisimide (PBI) and azo-compounds are fascinating molecules with interesting optical properties. Here, we combine the two chromophores to prepare nonconjugated and conjugated stable azo-PBI dyes. The detailed structural characterization, comparison of properties, and solid-state self-assembly of the compounds are discussed. The incorporation of azo groups at the bay side of PBI led to significant changes in optical properties as compared to the model PBIs (M1 and M2). All new azo-PBIs showed photoinduced isomerization, which caused disaggregation and enhancement in fluorescence. The amine-incorporated azo-PBIs (3 and 6) reduced chloroauric acid into gold nanoparticles. The current study offers a simple synthetic strategy and comparison of the properties of conjugated and nonconjugated azo-PBIs, which could be useful in photoelectronic devices.

A Naphthalene Diimide Based Macrocycle Containing Quaternary Ammonium Groups: An Electron-Deficient Host for Aromatic Carboxylate Derivatives.

Naphthalene diimide (NDI) compounds are widely used as electron acceptors in various applications. Herein, we combine NDI with quaternary ammonium groups for the synthesis of a highly electron-deficient linear compound 2 and macrocycle 3. The complexation studies of the water-soluble macrocycle 3 with aromatic di- and tetra- carboxylate anions in water were done using absorption, emission, 1 H NMR and NOESY spectroscopic titrations. The NDI incorporated macrocycle 3 showed high binding affinities towards linear aromatic tetracarboxylate anions owing to the size and charge complementarity of the host-guest complex. Macrocycle 3 binds tetracarboxylate anion much better than dicarboxylate anions. Furthermore, the macrocycle 3 is solvated differently in acetonitrile and in water or dimethyl sulfoxide, which induces changes in conformation and photophysical properties. Such electron-deficient optically active macrocycles are useful for developing useful sensor materials.

Tubular Perylene Bisimide Macrocycles for the Recognition of Geometrical Isomers of Azobenzenes.

Perylene bisimide-based materials are good candidates for photosensitive applications. Herein, we report synthesis, characterization, and complexation studies of perylene bisimide macrocycles obtained through bayside coupling. The isomeric macrocycles incorporated with interesting optical properties and tubular-shaped cavities are able to recognize geometric isomers of azobenzenes and aromatic amines. Such selective recognition is useful toward developing potential sensors for interesting isomeric pairs in the future.