Search

Aromatic carboxylic acids are prone to decarboxylate in high-temperature water (HTW). While the decarboxylation kinetics of several aromatic carboxylic acids have been explored, studies on their compatibility with organic syntheses in HTW are scarce. Herein, we report the hydrothermal synthesis (HTS) of 2,3-diarylquinoxaline carboxylic acids from 1,2-diarylketones and 3,4-diaminobenzoic acid. A detailed study of the reaction parameters was performed to identify reaction conditions towards minimal decarboxylation. Thirteen 2,3-diarylquinoxaline-6-carboxylic acids are obtained at temperatures between 150–230 °C within 5–30 minutes. The reported conditions feature comparable performance to those of classic syntheses, avoiding volatile organic solvents, strong acids and toxic catalysts. Decarboxylated quinoxalines arise as side products in variable amounts via direct decarboxylation of the 3,4-diaminobenzoic acid. To completely inhibit the decarboxylation, we show that suitable structural analogues of 3,4-diaminobenzoic acid can act as starting compounds. Thus, ester hydrolysis of methyl 3,4-diaminobenzoate and deprotection of di-Boc-protected 3,4-diminobenzoic can be coupled with the HTS of quinoxaline towards quinoxaline carboxylic acids, while fully avoiding decarboxylated side products.

Herein, we synthesized a series of siloxane-based poly(ionic liquid)s (PILs) with imidazolium-type species in the main chain via the multicomponent Debus–Radziszewski reaction. We employed oligodimethylsiloxane diamine precursors to integrate flexible spacers in the polymer backbone and ultimately succeeded in obtaining main-chain PILs with low glass transition temperatures (Tgs) in the range of −40 to −18 °C. Such PILs were combined with conventional hydrophobic vinylimidazolium-based PILs for the fabrication of porous membranes via interpolyelectrolyte complexation with poly(acrylic acid), which leads to enhanced mechanical performance in the tensile testing measurements. This study will enrich the structure library of main-chain PILs and open up more opportunities for potential industrial applications of porous imidazolium-based membranes. published

Noble metal nanoparticles anchored on flexible polyurethane foams were synthesized by hydrothermal synthesis. Through employing a robotic arm, these ‘catalytic sponges’ were used for organic reductions towards automated lab-scale organic synthesis.

Herein, we report a simple and versatile synthetic approach towards siloxane-based poly(ionic liquid)s (PILs) with unusually low glass transition temperatures (Tg) down to −73°C, and thus “liquid-like” behavior at room temperature. We designed a polydimethylsiloxane-derived copolymer carrying dialkylimidazolium moieties, and by careful selection of the side-chain length and the type of anions we were able to manipulate its Tg over a wide range and reach high ionic conductivities (σDC) up to 4.8 × 10−5 S/cm at 300 K. The ionized species make up only a minor fraction (

Cisplatin induces DNA crosslinks that are highly cytotoxic. Hence, platinum complexes are frequently used in the treatment of a broad range of cancers. Efficiency of cisplatin treatment is limited by the tumor-specific DNA damage response to the generated lesions. We reasoned that better tools to investigate the repair of DNA crosslinks induced by cisplatin would therefore be highly useful in addressing drug limitations. Here, we synthesized a series of cisplatin derivatives that are compatible with click chemistry, thus allowing visualization and isolation of DNA-platinum crosslinks from cells to study cellular responses. We prioritized one alkyne and one azide Pt(II) derivative, Pt-alkyne-53 and Pt-azide-64, for further biological characterization. We demonstrate that both compounds bind DNA and generate DNA lesions and that the viability of treated cells depends on the active DNA repair machinery. We also show that the compounds are clickable with both a fluorescent probe as well as biotin, thus they can be visualized in cells, and their ability to induce crosslinks in genomic DNA can be quantified. Finally, we show that Pt-alkyne-53 can be used to identify DNA repair proteins that bind within its proximity to facilitate its removal from DNA. The compounds we report here can be used as valuable experimental tools to investigate the DNA damage response to platinum complexes and hence might shed light on mechanisms of chemoresistance.

Herein, we synthesized a series of siloxane-based poly(ionic liquid)s (PILs) with imidazolium-type species in the main chain

Herewith, we report a straightforward, experimentally simple, and environmentally benign synthetic strategy toward cyclocondensation polymers. Using a fully aromatic polyimide as model system, we d...

Carbon fiber reinforced Plastics are materials with high strength and stiffness at low weight compared to metals. These properties make the materials ideal candidate for structures in aerospace applications, where they are often used under bending conditions. Due to the strongly anisotropic composition the CFRP typically fail in compression by fiber buckling. In order to improve this weakness, nanotube and nanofiber reinforced matrix was used to build CFRP. Four-point bending tests showed that stiffness and strength could be improved by the fillers, whereas negative influence was found on fracture energy.

A simple route for the in-situ orientation of carbon nanofillers applied during the curing process of a carbon fiber reinforced polymer (CRFP) in a hot press, is demonstrated. Neat MWCNT, amine-functionalized MWCNT (MWCNT-NH2) and CNF were dispersed in an epoxy resin using a three-roll-mill (TRM) to ensure good dispersion. The process leads to a hierarchically structured functional composite where MWCNT/CNF are aligned in the z-direction (out-of-plane) of the carbon fiber plies, giving rise to improved mechanical and electrical performance. Our results demonstrate that aligned carbon nanofillers yield significantly more pronounced improvements than non-oriented fillers. An applicable processing route towards advanced functional composite materials with major practical importance is presented in this study.

The pursuit of CO2 reduction targets has increased the need of storage capacities for renewable energy or thermal energy to enhance the efficiency of industrial processes. To combine the benefits of latent and sensible thermal energy storage systems, the concept of micro encapsulated phase change material is presented. The microparticles are designed to work in a high-temperature thermal energy storage system considering economic and technical points of view. Therefore, particles of sodium nitrate are physio-mechanical coated with polyimide by using spray-drying in a fluidized bed reactor. To evaluate the influence of the process conditions, several coating experiments with different process settings are performed. Afterward, the samples are analyzed to determine their properties. Besides a microscopic and a sieving analysis, they are tested in the laboratory to define their mechanical and thermal limits. Finally, a rough layout of a thermal energy storage system using the produced particles is presented and compared to a common sensible thermal energy storage.

In organic-inorganic hybrid materials' (HMs) synthesis, it is intrinsically challenging to, at the same time, achieve (i) the concomitant synthesis of the components, (ii) nanoscopic interpenetration of the components, and (iii) covalent linking of the components. We here report the one-pot hydrothermal synthesis (HTS) of inorganic-organic HMs consisting of perylene bisimide (PBI) dyes and silica, using nothing but water as the medium and directly from the corresponding bisanhydrides

Here, the hydrothermal synthesis (HTS) of 2,3‐diarylquinoxalines from 1,2‐diketones and o‐phenylendiamines (o‐PDAs) was achieved. The synthesis is simple, fast, and generates high yields, without requiring any organic solvents, strong acids or toxic catalysts. Reaction times down to 90 % in all cases). Moreover, it was shown that HTS has high compatibility: (i) hydrochlorides, a standard commercial form of amines, could be used directly as combined amine source and acidic catalyst, and (ii) Boc‐diprotected o‐PDA could be directly employed as substrate that underwent HT deprotection. A systematic large‐scale computational comparison of all reported syntheses of the presented quinoxalines from the same starting compounds showed that this method is more environmentally friendly and less toxic than all existing methods and revealed generic synthetic routes for improving reaction yields. Finally, the application of the synthesized compounds as fluorescent dyes for cell staining was explored., In hot water: 2,3‐Diarylquinoxalines and biquinoxalines are synthesized in a rapid, efficient and green fashion in nothing but high‐temperature water. Through a large‐scale computational analysis, the herein reported reaction conditions are compared with all reported syntheses of the presented compounds.

We report on the hydrothermal polymerization (HTP) of polyimide (PI) networks using the medium H2O and the comonomers 1,3,5-tris(4-aminophenyl)benzene (TAPB) and pyromellitic acid (PMA). Full condensation is obtained at minimal reaction times of only 2 h at 200 °C. The PI networks are obtained as monoliths and feature thermal stabilities of >500 °C, and in several cases even up to 595 °C. The monoliths are built up by networks of densely packed, near-monodisperse spherical particles and annealed microfibers, and show three types of porosity: (i) intrinsic inter-segment ultramicroporosity (48 h), also PI/SiO2 hybrids that form through reaction with the reaction vessel. Moreover, we have developed a computational image analysis pipeline that deciphers the complex morphologies of these SEM images automatically and also allows for formulating a hypothesis of morphology development in HTP that is in good agreement with the manual morphology analysis. Finally, we upscaled the HTP of PI(TAPB–PMA) and processed the resulting powder into dense cylindrical specimen by green solvent-free warm-pressing, showing that one can follow the full route from the synthesis of these PI networks to a final material without employing harmful solvents., We report on the hydrothermal polymerization (HTP) of porous polyimide (PI) networks using the medium H2O and the comonomers 1,3,5-tris(4-aminophenyl)benzene (TAPB) and pyromellitic acid (PMA).

Hochkondensierte, vollständig konjugierte aromatische Verbindungen sind interessante Kandidaten zur Anwendung in organischer Elektronik. Mit steigender Kristallinität verbessern sich ihre elektronischen Eigenschaften. Hier wird gezeigt, dass die Kristallisation von drei Archetypen solcher Moleküle – Pentacentetron, Indigo und Perinon – hydrothermal erreicht werden kann. Dieser Befund ist angesichts der Strukturen dieser Verbindungen höchst erstaunlich. Darüber hinaus wird gezeigt, dass Perinon ausgehend von Naphthalinbisanhydrid und o-Phenylendiamin in ausschließlich hochtemperiertem Wasser und ohne Zusatz von Cosolventien oder Katalysatoren hergestellt werden kann. Weiterhin kann die Transformation durch den Einsatz von Mikrowellen-Strahlung drastisch beschleunigt werden. Dies ist der erste Bericht über die hydrothermale Herstellung von zwei kondensierten Heterocyclen. published

Miriam M. Unterlass introduces a Journal of Materials Chemistry/Materials Advances Editor's choice web collection on recent advances in hydrothermal materials synthesis (https://rsc.li/hydrothermal).

Carbon fiber reinforced polymers (CFRPs) are promising composite materials for high-performance and lightweight applications, gaining increasing interest in aerospace and automotive industries. Epoxy thermosets are frequently used as polymer matrices of CFRPs, which are usually responsible for failure of the composite. In this work different types of carbon nanotubes (CNTs) and carbon nanofibers (CNF) are added to the epoxy resin to improve mechanical properties of the whole CFRP composite. The dispersion of the fillers on a three-roll mill (TRM) is shown comparing their dispersion behavior in the resin. Results of increased modulus and strength of the hierarchical composite in four-point bending tests are presented.

Verschiedene Polyimide und Polyamide wurden in letzter Zeit durch hydrothermale Synthese in nichts als H2O unter Hochdruck- und Hochtemperaturbedingungen hergestellt. Keines dieser Polymere weist jedoch ein konjugiertes Polymerrückgrat auf. Hiermit berichten wir über eine Erweiterung des synthetischen Anwendungsbereichs dieser einfachen und von Natur aus umweltfreundlichen Polymerisationstechnik auf die Herstellung von konjugierten Polymeren. Ausgewählte Vertreter von zwei verschiedenen Polymerklassen, Pyrronpolymere und Polybenzimidazole, wurden hydrothermal synthetisiert. Neben einer mechanistischen Diskussion der Polymerbildung wird auch eine elektrochemische Charakterisierung des vielversprechendsten Produktes präsentiert. published

High-purity, symmetrically substituted perylene and naphthalene bisimides were obtained by hydrothermal condensation of monoamines with the corresponding bisanhydride. The hydrothermal imidization proceeds quantitatively, without the need for organic solvents, catalysts or excess of the amines. published

The term “inorganic–organic hybrid materials” designates inorganic building blocks in the colloidal domain (1–1000 nm) embedded in an organic, typically polymeric, matrix. Owing to their outstanding properties, hybrid materials have the potential to improve human life significantly. In the last two decades, the importance of reorienting chemical syntheses in the direction of more sustainable, less harmful and energy-consuming procedures, referred to as green chemistry, has been much emphasized and worked on. This review deals with the application of green chemistry to the synthesis of inorganic–organic hybrid materials. The origin and preparation both of the inorganic components and of the organic polymer matrix are critically analyzed for various examples. The development of more sustainable syntheses for hybrid materials still poses an open challenge. Potential options to tackle this task are discussed.

Hydrothermal polymerization (HTP) is a technique to synthesize highly crystalline polyimides in solely water. The process involves monomer salt intermediates also able to undergo other polymerizations during the HTP experiment: sub-hydrothermal polymerization (sHTP) and solid-state polycondensation (SSP). Both processes yield semicrystalline polyimides at best. This is widely believed to result from irreversible bond-formation and the incorporation of conformational defects during chain growth. Here, microwave-assisted HTP is used, allowing for controlling the heating time to the reaction temperature, and thus to strongly reduce sHTP. Moreover, we show that highest crystallinity can be obtained in the higher hydrothermal regime (≈200 °C), and synthesize two polyimides of sufficient crystallinity to refine their crystal structures from powder X-ray diffraction data. This study brings us one step closer to a general picture and rational design of the hydrothermal synthesis of polyimides.

Shape-anisotropic particles are of broad interest, e.g., for colloidal crystals or applications at interfaces such as particle-stabilized emulsions. Despite the wealth of accessible shapes of inorganic particles, anisotropic homopolymer particles are to date mostly limited to objects derived from spheres (e.g., ellipsoidal or disk-shaped particles). Here, we report the synthesis of shape-anisotropic, angular polyimide particles by thermal solid-state polycondensation (SSP) of monomer salts. We prepare monomer salt single crystals of relatively narrow size and shape distribution by growth inside hydrogels, and solve their crystal structure. Polyimide particles are obtained by simple heating and retain the shape of the initial salt crystals. Using high-temperature X-ray diffraction, thermal analyses and microscopy techniques, we investigate the mechanism of the transformation. The obtained polyimide particles are temperature-stable up to 640 °C and virtually insoluble in any solvent. This work sheds more li...

Highly fused, fully conjugated aromatic compounds are interesting candidates for organic electronics. With higher crystallinity their electronic properties improve. It is shown here that the crystallization of three archetypes of such molecules-pentacenetetrone, indigo, and perinone-can be achieved hydrothermally. Given their molecular structure, this is a truly startling finding. In addition, it is demonstrated that perinone can also be synthesized in solely high-temperature water from the starting compounds naphthalene bisanhydride and o-phenylene diamine without the need for co-solvents or catalysts. The transformation can be drastically accelerated by the application of microwave irradiation. This is the first report on the hydrothermal generation of two fused heterocycles. published

Hydrothermal polymerization (HTP) has been recently established as a novel route to synthesize polyimides of outstanding crystallinity. In this contribution, we lay out the basic theoretical and experimental framework for understanding the mechanistic underpinnings of this process. For this purpose, we hydrothermally synthesize two representative polyimides that are known to form amorphous polymers when synthesized classically. Hydrothermal polymerization, in contrast, yields unprecedented crystallinity after only two hours. The co-monomers diamine and dianhydride form monomer salts via acid–base reaction when brought in contact in water. We show that the physicochemical properties of the crystalline monomer salts (i.e. solubility, solid-state polymerization temperature) are important factors for the crystallinity and the morphology of the corresponding hydrothermally synthesized polyimide. We develop a mechanistic model of hydrothermal polymerization processes allowing us to relate the polymerization parameters (concentration, reaction temperature, reaction time) to the obtained polyimide crystallinity and morphology. By adjusting the parameters, the achieved crystallinity can be further increased and high morphological homogeneity can be obtained. We believe that the developed mechanistic picture is applicable for the hydrothermal polymerization of any polyimide.

In hot water: Hydrothermal crystallization was recently used to transform amporphous polymer networks into amide-linked, stable covalent-organic frameworks. This work is highlighted in the context of the synthesis and especially crystallization of organic materials by using high-temperature water.

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich. This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively. Inspired by geological ore formation processes, we apply one-step hydrothermal (HT) polymerization to the toughest existing high-performance polymer, poly(p-phenyl pyromellitimide) (PPPI). We obtain highly-ordered and fully imidized PPPI as crystalline flakes and flowers on the micrometer scale. In contrast to classical 2-step procedures that require long reaction times and toxic solvents and catalysts, HT polymerization allows for full conversion in only 1 h at 200 °C, in nothing but hot water. Investigation of the crystal growth mechanismviascanning electron microscopy (SEM) suggests that PPPI aggregates formviaa dissolution–polymerization–crystallization process, which is uniquely facilitated by the reaction conditions in the HT regime. A conventionally prefabricated polyimide did not recrystallize hydrothermally, indicating that the HT polymerization and crystallization occur simultaneously. The obtained material shows excellent crystallinity and remarkable thermal stability (600 °C under N2) that stem from a combination of a strong, covalent polymer backbone and interchain hydrogen bonding.

Vitrimers, strong organic glass formers, are covalent networks that are able to change their topology through thermoactivated bond exchange reactions. At high temperatures, vitrimers can flow and behave like viscoelastic liquids. At low temperatures, exchange reactions are very long and vitrimers behave like classical thermosets. The transition from the liquid to the solid is reversible and is, in fact, a glass transition. By changing the content and nature of the catalyst, we can tune the transesterification reaction rate and show that the vitrimer glass transition temperature and the broadness of the transition can be controlled at will in epoxy-based vitrimers. This opens new possibilities in practical applications of thermosets such as healing or convenient processability in a wide temperature range.

Cryo-electron microscopy, atomic force microscopy, and light microscopy investigations provide experimental evidence that amphiphilic emulsion copolymerization particles change their morphology in dependence on concentration. The shape of the particles is spherical at solids content above 1%, but it changes to rod-like, ring-like, and web-like structures at lower concentrations. In addition, the shape and morphology of these particles at low concentrations are not fixed but very flexible and vary with time between spheres, flexible pearl-necklace structures, and stretched rods.

published

A mechanistic study regarding the synthesis of aromatic polyimides (PIs) under hydrothermal conditions is presented. We demonstrate evidence that the first step of the reaction is the formation of a nylon type salt, which can be isolated. Upon heating the salt in the presence of water at 180 °C, polyimides are formed from the salts. Additionally performed DFT calculations substantiate the experimental findings and give evidence that the formation of imides is energetically favorable in hot water. The intermediate salts as well as the resulting PIs are characterized by diverse analytical techniques (SEC, FT-IR, WAXS, SEM). By selective fractionation, it is possible to obtain polyimides of moderate to high molecular weights that form tough films. The polymerization mechanism is discussed, and it is shown that different loci of reaction are possible, namely interfacial polycondensation, heterophase polymerization and topochemical transformations, which seem to occur in parallel. Finally, poloxamers can be used as additives for the fine-tuning of the polymer morphology.