Examinando por Autor "De la Fuente, J. L."

Mostrando 1 - 18 de 18

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A Comparative Study on HCN Polymers Synthesized by Polymerization of NH4CN or Diaminomaleonitrile in Aqueous Media: New Perspectives for Prebiotic Chemistry and Materials Science
(Chemistry Europe: European Chemical Societies Publishing, 2019-08-02) Ruiz Bermejo, Marta; De la Fuente, J. L.; Carretero González, J.; García Fernández, L.; Rosa Aguilar, M.; Agencia Estatal de Investigación (AEI); Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
HCN polymers are a group of complex and heterogeneous substances that are widely known in the fields of astrobiology and prebiotic chemistry. In addition, they have recently received considerable attention as potential functional material coatings. However, the real nature and pathways of formation of HCN polymers remain open questions. It is well established that the tuning of macromolecular structures determines the properties and practical applications of a polymeric material. Herein, different synthetic conditions were explored for the production of HCN polymers from NHCN or diaminomaleonitrile in aqueous media with different concentrations of the starting reactants and several reaction times. By using a systematic methodology, both series of polymers were shown to exhibit similar, but not identical, spectroscopic and thermal fingerprints, which resulted in a clear differentiation of their morphological and electrochemical properties. New macrostructures are proposed for HCN polymers, and promising insights are discussed for prebiotic chemistry and materials science on the basis of the experimental results.
Acceso Abierto
A Comprehensive Review of HCN-Derived Polymers
(Multidisciplinary Digital Publishing Institute (MDPI), 2021-03-29) Ruiz Bermejo, Marta; De la Fuente, J. L.; Pérez Fernández, Cristina; Mateo Martí, Eva; Ruiz Bermejo, M. [0000-0002-8059-1335]; Mateo Martí, E. [0000-0003-4709-4676]; Unidad de Excelencia Científica María de Maeztu del Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
HCN-derived polymers are a heterogeneous group of complex substances synthesized from pure HCN; from its salts; from its oligomers, specifically its trimer and tetramer, amino-nalono-nitrile (AMN) and diamino-maleo-nitrile (DAMN), respectively; or from its hydrolysis products, such as formamide, under a wide range of experimental conditions. The characteristics and properties of HCN-derived polymers depend directly on the synthetic conditions used for their production and, by extension, their potential applications. These puzzling systems have been known mainly in the fields of prebiotic chemistry and in studies on the origins of life and astrobiology since the first prebiotic production of adenine by Oró in the early years of the 1960s. However, the first reference regarding their possible role in prebiotic chemistry was mentioned in the 19th century by Pflüger. Currently, HCN-derived polymers are considered keys in the formation of the first and primeval protometabolic and informational systems, and they may be among the most readily formed organic macromolecules in the solar system. In addition, HCN-derived polymers have attracted a growing interest in materials science due to their potential biomedical applications as coatings and adhesives; they have also been proposed as valuable models for multifunctional materials with emergent properties such as semi-conductivity, ferroelectricity, catalysis and photocatalysis, and heterogeneous organo-synthesis. However, the real structures and the formation pathways of these fascinating substances have not yet been fully elucidated; several models based on either computational approaches or spectroscopic and analytical techniques have endeavored to shed light on their complete nature. In this review, a comprehensive perspective of HCN-derived polymers is presented, taking into account all the aspects indicated above.
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A dual perspective on the microwave-assisted synthesis of HCN polymers towards the chemical evolution and design of functional materials
(Nature Research Journals, 2020-12-18) Hortal, Lucia; Pérez Fernández, Cristina; De la Fuente, J. L.; Valles González, M. P.; Mateo Martí, Eva; Ruiz Bermejo, Marta; Instituto Nacional de Técnica Aeroespacial (INTA); Agencia Estatal de Investigación (AEI); http://dx.doi.org/10.13039/501100011033; http://dx.doi.org/10.13039/501100010687; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
In this paper, the first study on NH4CN polymerization induced by microwave radiation is described, where a singular kinetic behaviour, especially when this reaction is conducted in the absence of air, is found. As a result, a complex conjugated N-heterocyclic polymer system is obtained, whose properties are very different, and even improved according to morphological features, characterized by their X-ray diffraction patterns and scanning electron microscopy analysis, with respect to those produced under conventional thermal treatment. In addition, a wide variety of relevant bioorganics have been identified, such as amino acids, nucleobases, co-factors, etc., from the synthetized NH4CN polymers. These particular families of polymers are of high interest in the fields of astrobiology and prebiotic chemistry and, more recently, in the development of smart multifunctional materials. From an astrobiological perspective, microwave-driven syntheses may simulate hydrothermal environments, which are considered ideal niches for increasing organic molecular complexity, and eventually as scenarios for an origin of life. From an industrial point of view and for potential applications, a microwave irradiation process leads to a notable decrease in the reaction times, and tune the properties of these new series macromolecular systems. The characteristics found for these materials encourage the development of further systematic research on this alternative HCN polymerization.
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Adhesives Based on Poly(glycidyl methacrylate-co-butyl acrylate) with Controlled Structure: Curing Behavior and Adhesion Properties on Metal Substrates
(Wiley, 2023-10-26) Cañamero, Pedro; Fernández García, Marta; De la Fuente, J. L.; Ministerio de Ciencia e Innovación (MICINN); Instituto Nacional de Técnica Aeroespacial (INTA)
The adhesion properties of poly(glycidyl methacrylate (GMA)-co-butyl acrylate (BA)) statistical copolymers, synthesized by atom transfer radical polymerization (ATRP), are investigated employing three different curing agents or hardeners, such as diethanolamine (DEA), dicyandiamide (DICY), and 2-cyanoacetamide (2-CA) on copper, iron, brass, aluminum, and titanium metal surfaces. This work describes the treatment of the different surfaces, establishes the optimal curing conditions from differential scanning calorimetry (DSC) analysis of these novel adhesive systems, and evaluates the results of the single-lap shear test for metal joints. Thus, by dynamic DSC measurements of the mixtures, a low curing temperature of 90 °C is defined when DEA is used as a curative; while systems based on DICY and 2-CA require temperatures of 150 °C and 160 °C, respectively. In addition, the curing process of this controlled acrylic copolymer with DICY exhibits a singular behavior, possibly due to the curing reaction mechanism, where multiple epoxy-amine ring-opening polyaddition reactions take place between DICY's active hydrogens and epoxy groups of poly(GMA-co-BA). This latter curing system shows the highest adhesion features with lap-shear strength at room temperature of 15.5 MPa, using copper as metallic substrate; however, the best results are obtained using 2-CA as curing agent with aluminum and iron.
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Air effect on both polymerization kinetics and thermal degradation properties of novel HCN polymers based on diaminomaleonitrile
(Elsevier, 2022-12) Hortelano, C.; Ruiz Bermejo, Marta; De la Fuente, J. L.; Instituto Nacional de Técnica Aeroespacial (INTA); Ministerio de Ciencia, Innovación y Universidades (MICIN); Agencia Estatal de Investigación (AEI); Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
The impact of air on the bulk polymerization kinetics of diaminomaleonitrile (DAMN), tetramer of HCN, and thermal degradation properties of this resulting conjugated C=N polymeric system is investigated under different temperature regimes and environments. This study shows the effect of exposure to air and oxygen, time, temperature, and evolved gases during DAMN polymerization reactions, which can be suitably monitored by differential scanning calorimetry (DSC) through both dynamic and isothermal measurements. Thus, low heating rates and isothermal scans at 150-170 °C allow us to describe the solid-state polymerization (SSP) of DAMN, and those experiments at 190, 195 and 200 °C and higher heating runs define its melt polymerization (MP) behaviour. Both processes are highly efficient, possibly due to the self-acceleration nature of their kinetics, which is consistent with a three-step Šesták-Berggren (SB) model. The oxygen effect was analysed to determine their tolerance to this variable and confirm the nonradical nature of the mechanism under study. In addition, a detailed thermal characterization by simultaneous DSC/thermogravimetry coupled to mass spectrometry (TG-MS) of these singular polymeric systems obtained under air atmosphere has been completed, and the improvement of the thermal stability of those samples prepared by an SSP at lower temperature was confirmed. The present work offers lower-cost and simpler synthetic methods to obtain this novel class of promising multifunctional polymeric materials through highly efficient and very fast processes.
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Ammonium affects the wet chemical network of HCN: feedback between prebiotic chemistry and materials science
(Royal Society of Chemistry, 2023-06-21) De la Fuente, J. L.; Vega, Jorge; Mateo Martí, Eva; Valles González, M. P.; Ruiz Bermejo, Marta; Pérez Fernández, Cristina; Instituto Nacional de Técnica Aeroespacial (INTA); Universidad Complutense de Madrid (UCM); Agencia Estatal de Investigación (AEI); Consejo Superior de Investigaciones Científicas (CSIC); Ministerio de Ciencia, Innovación y Universidades (MICINN)
Prebiotic chemistry one-pot reactions, such as HCN-derived polymerizations, have been used as stimulating starting points for the generation of new multifunctional materials due to the simplicity of the processes, use of water as solvent, and moderate thermal conditions. Slight experimental variations in this special kind of polymerization tune the final properties of the products. Thus, herein, the influence of NH4Cl on the polymerization kinetics of cyanide under hydrothermal conditions and on the macrostructures and properties of this complex system is explored. The kinetics of the process is consistent with an autocatalytic model, but important variations in the polymerization reaction are observed according to a simple empirical model based on a Hill equation. The differences in the kinetic behaviour against NH4Cl were also revealed when the structural, morphological, thermal, electronic and magnetic properties of the synthesized cyanide polymers were compared, and these properties were evaluated by elemental analysis, FTIR, XPS, UV-vis, and ESR spectroscopies, X-ray diffraction, SEM and thermoanalytical techniques. As a result, this hydrothermal prebiotic polymerization is not only pH dependent, as previously thought, but also ammonium subservient. From this result, a hypothetical reaction mechanism was proposed, which involves the active participation of ammonium cations via formamidine and serves as a remarkable point against previous reports. The results discussed here expand the knowledge on HCN wet chemistry, offer an extended view of the relevant parameters during the simulation of hydrothermal scenarios and describe the production of promising paramagnetic and semiconducting materials inspired by prebiotic chemistry.
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Catalytic effects over formation of functional thermoplastic elastomers for rocket propellants
(Wiley, 2021-11-22) Lucio, B.; De la Fuente, J. L.; Ministerio de Ciencia e Innovación (MICINN); Instituto Nacional de Técnica Aeroespacial (INTA); Gobierno Vasco
Rheometry was the main method to characterize the curing process of binders made of functional polyurethanes (PUs). The macroglycols characterization by means of additional techniques such as nuclear magnetic resonance, size exclusion chromatography and differential scanning calorimetry, provided further information for the chemorheological description. Materials were based on Butacene ((ferrocenylbutyl)dimethylsilane grafted to hydroxyl-terminated polybutadiene (HTPB)), used in the solid propulsion field. First, the flow parameters for the uncured reactive mixtures of Butacene and four different diisocyanates were analysed via viscometry and these were markedly influenced by the chemical structure of the curing agents. Analysing the rheokinetic constant values of the pre-gel stage for Butacene- and HTPB-reactive systems, relevant catalysis caused by the ferrocene moiety was detected when aliphatic reactants were used, such as isophorone diisocyanate or 1,6-hexamethylene diisocyanate (IPDI and HMDI, respectively). No catalytic effect was found for 2,4-toluene diisocyanate (2,4-TDI) or even for 4,4’-methylenediphenyl diisocyanate (4,4’-MDI). Finally, the use of dynamic rheology was useful to evaluate the critical points during gelation process, where the reactivity of curing agents was associated with the achievement of elastic properties. Both techniques agreed the reactivity order of curing agents with Butacene, which is 4,4’-MDI > HMDI >> 2,4-TDI ≥ IPDI. The knowledge of the structure-reactivity relationship and, moreover, the kinetics of the urethane network formation for these metallo-PUs is paramount in manufacturing processes for advanced thermoplastic elastomer applications.
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Chemorheology and Kinetics of High-Performance Polyurethane Binders Based on HMDI
(Wiley Online Library, 2021-01-21) Lucio, B.; De la Fuente, J. L.; Agencia Estatal de Investigación (AEI); Gobierno Vasco
Aliphatic diisocyanates, such as 1,6-hexamethylene diisocyanate (HMDI), are preferred curing agents for the formation of polyurethanes (PUs) in applications where resistance to abrasion or degradation by ultraviolet light takes precedence. Aside from the final properties, the curing agent plays a key role in the bulk manufacturing of such materials, and it mainly affects the polymerization kinetics and their rheology. The copolymerization of HMDI and a metallo-prepolymer derivative from hydroxyl-terminated polybutadiene (HTPB) is studied under isothermal conditions (50–80 °C). This study is carried out by means of an indirect method, using both rotational viscometry and dynamic rheometry. At the beginning of the process, the viscosity growth fit well to a first-order kinetic model. Afterward, the reactive system passes through gelation, from which only rheology is allowed for the investigation of the entire polymerization process. This transition is analyzed in depth together with predictions from percolation theory. The conversion degree is determined from rheological measurements, and then an autocatalytic kinetic model is applied to describe the overall process. Finally, an isoconversional method allows the evolution of activation energy to be studied. This analysis merits attention for the development of high-performance binders that are of great interest in aerospace propulsion technology.
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HCN-derived polymers from thermally induced polymerization of diaminomaleonitrile: A non-enzymatic peroxide sensor based on prebiotic chemistry
(Elsevier, 2021-11-24) Ruiz Bermejo, Marta; García Armada, Pilar; Mateo Martí, Eva; De la Fuente, J. L.; Ministerio de Ciencia e Innovación (MICINN); Instituto Nacional de Técnica Aeroespacial (INTA); Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
HCN-derived polymers have recently attracted considerable attention due to their promising applications as multifunctional materials. This study, inspired by plausible early Earth geochemical conditions, describes a strategy to synthesize them from the self-initiated thermal bulk polymerization of the HCN tetramer, diaminomaleonitrile (DAMN), with outstanding sensing properties. These conjugated polymers were obtained through noncatalysed and simple isothermal reactions at 170 °C in the solid-state, and experiments at 190 °C permitted polymerization in the melt. Both processes are highly efficient, allowing quantitative yields of the end products. The conductivity properties of both polymers have been explored to show their high potential, especially DAMN polymers synthesized in melt, as nonenzymatic peroxide sensors. To better understand the differences found between the two series, structural characterisation was carried out using compositional data, Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR) and X-ray photoelectron (XPS) spectroscopies, and X-ray diffraction (XRD) measurements. The interpretation of the structural data suggests that a two-dimensional (2-D) macrostructure based on N-heterocyclics is predominant regardless of the state of monomer aggregation during the course of polymerization, but preferably formed in the melt. The morphological and thermal stability properties of the polymers based on DAMN were also evaluated. Finally, the most likely mechanisms based on the dehydrocyanation and deamination reactions that take place during the polymerization reaction are proposed. This study demonstrates the robust and straightforward character of these thermally activated polymerizations, which are of interest to chemical evolution research and to current materials and surface science.
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Highly efficient melt polymerization of diaminomaleonitrile
(Elsevier BV, 2021-01-15) Mas, I.; Hortelano, C.; Ruiz Bermejo, Marta; De la Fuente, J. L.; Agencia Estatal de Investigación (AEI); 0000-0002-8059-1335; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
HCN polymers are of great interest in research on the origin of life and, currently, in materials science because they have shown potential for the design of electrical devices, (photo)catalysts and biomedicine. Herein, calorimetric measurements have successfully described the bulk polymerization of HCN tetramer, diaminomaleonitrile (DAMN). Two series of nonisothermal experiments were carried out by differential scanning calorimetry (DSC), and low-heating rate (β) the thermograms (β ≤ 5 °C/min) indicated that the polymerization is initiated at temperatures lower than the DAMN melting point, ~180 °C; while higher heating rates results in a rapid polymerization reaction, which occurs entirely in the liquid phase. The DSC data were analysed using model-free linear iso-conversional methods to estimate kinetic parameters, such as activation energy, and a suitable kinetic model was proposed for these thermal polymerizations in the melt. A preliminary structural and morphological characterization by means of Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) was also completed. This study demonstrated the autocatalytic, highly efficient and straightforward character of this stimulated thermal polymerization of DAMN and, to the best of our knowledge, describes for the first time a systematic and extended kinetic analysis to gain mechanistic insights into this process. The latter was done through the help of simultaneous thermogravimetry (TG)-DSC and in situ mass spectrometry (MS) technique to investigate the gas products generated during these melt polymerizations. These analyses revealed that deamination and dehydrocyanation processes are two relevant reactions involved in DAMN polymerization mechanism.
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Kinetic and chemorheological modelling of the polymerization of 2,4- Toluenediisocyanate and ferrocene-functionalized hydroxyl-terminated polybutadiene
(Elsevier, 2018-02-26) Lucio, B.; De la Fuente, J. L.; Ministerio de Economía y Competitividad (MINECO)
The reaction of 2,4-toluenediisocyanate (2,4-TDI) and a metallocenic-prepolymer derived from hydroxyl-terminated polybutadiene (HTPB) was studied in bulk and under isothermal conditions (50–80 °C) by rheological methods. Two regions distinguished and limited by the gel point, identified as the crossover of loss tangent (tan δ) at different frequencies, were analysed from different rheological properties during the curing process of this novel metallo-polyurethane (PU). The initial part of this polymerization, dominated by the viscous behaviour (from η0 ≈ 5 Pa s to η = 250 Pa s), was modelled through the Arrhenius isothermal model, in which the presence of two rheokinetic stages, due to different isocyanate groups in the 2 and 4 positions for this asymmetric monomer, was found until the gelation is reached. The contributions of the main reactions for the region analysed, before the gel point of this polyaddition, are discussed. The gel transition was identified, and the viscoelastic behaviour of the gelation process was studied in depth. In addition, from the evolution of the storage modulus (G′) recorded, the overall polymerization reaction was described by a Kamal-Sourour kinetic expression for the reaction rate. The different kinetic parameters obtained for the autocatalytic model used yielded predictions that agree very well with the experimental data, finding a significant autocatalytic effect. An isoconversional method allowed the determination of the dependence of the activation energy on the conversion degree during the network formation of this advanced functional ferrocene-PU, which is of great interest in rocket technology research for the development of the aerospace industry.
Acceso Abierto
Kinetic Study of the Effective Thermal Polymerization of a Prebiotic Monomer: Aminomalononitrile
(Multidisciplinary Digital Publishing Institute, 2023-01-17) Hortelano, C.; Ruiz Bermejo, Marta; De la Fuente, J. L.; Agencia Estatal de Investigación (AEI); Ministerio de Ciencia e Innovación (MICINN)
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Modelling the kinetics and structural property evolution of a versatile reaction: aqueous HCN polymerization
(Royal Society of Chemistry (RSC), 2018-05-29) Fernández, Amparo; Ruiz Bermejo, Marta; De la Fuente, J. L.; Ministerio de Economía y Competitividad (MINECO); Instituto Nacional de Técnica Aeroespacial (INTA)
The kinetics of the reaction of the synthesis of HCN polymers in aqueous medium at high temperatures have been analysed to ascertain a suitable model for this material, for which it was recently demonstrated that prebiotic chemistry may now be adapted in the development of a new generation of high performance coatings and adhesives with biomedical applications. These experimental conditions were chosen for the simplicity of the reagents, being particularly convenient in regard to potential industrial scale-up of coating technology, where these polymers have revealed an interesting field of application. The kinetics of the precipitation polymerization of HCN in water were studied under isothermal conditions at four different temperatures between 75 °C and 90 °C throughout gravimetric measurements. The use of the Kamal–Sourour autocatalytic kinetic model was proposed, properly describing the overall formation process of this insoluble HCN polymer. All of the kinetic parameters, including reaction orders, kinetic constants and activation energy, were determined for the cross-linking polymerization reaction under study, and a relevant autocatalysis effect was observed. An isoconversion method was also used to analyse the variation of the global activation energy with conversion; and characterization by means of elemental analysis, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) was carried out. This study demonstrates the autocatalytic, robust and straightforward character of this heterogeneous aqueous HCN polymerization, and to the best of our knowledge, this report describes the first time that a systematic and extended kinetic analysis has been conducted to obtain a more comprehensive and deeper understanding of this complex reaction, which is of great interest to the origin of life and, currently, to materials science.
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Rheological kinetics of ferrocenylsilane functionalized polyurethanes based on 4,4'-methylenediphenyl diisocyanate for advanced energetic materials
(Wiley, 2021-10-18) Lucio, B.; De la Fuente, J. L.; Ministerio de Ciencia e Innovación (MICINN); Gobierno Vasco
4,4’-Methylenediphenyl diisocyanate (4,4’-MDI) is a symmetric aromatic isocyanate commonly used as a curing agent in the production of polyurethanes (PUs). The chemorheology and kinetics of its reaction with a metallocenic-prepolymer derivative from hydroxyl-terminated polybutadiene (HTPB) is studied in bulk and under isothermal conditions at 50-80 °C by means of rheological measurements. The viscosity of the initial part of the PU formation, the pre-gel stage governed by viscous behaviour, is modelled through the Arrhenius rheokinetic model. This thermoplastic elastomer undergoes gelation, a transition that is analysed in depth together with predictions according to percolation theory. The gel point (tgel) is determined from the intersection in tan δ versus curing time for different shear frequencies. From the viscoelastic properties, like the elastic storage modulus (G´), the conversion degree is determined, and the entire polymerization process is modelled through the Kamal-Sourour and Sato kinetic expressions. Significant variation in the reaction orders and the activation energies might reveal a change in the process mechanism, depending on the temperature. This work demonstrates that an indirect method makes it possible to gain relevant knowledge about the chemistry of these thermoplastic PUs during curing, which is essential for their manufacturing. This study merits attention for the development of a new generation of high-performance binders with great potential in aerospace propulsion.
Acceso Abierto
Semiconducting Soft Submicron Particles from the Microwave-Driven Polymerization of Diaminomaleonitrile
(Multidisciplinary Digital Publishing Institute (MDPI), 2022-08-24) Ruiz Bermejo, Marta; García Armada, Pilar; Valles González, M. P.; De la Fuente, J. L.; Ministerio de Ciencia e Innovación (MICINN); Instituto Nacional de Técnica Aeroespacial (INTA); Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
The polymers based on diaminomaleonitrile (DAMN polymers) are a special group within an extensive set of complex substances, namely HCN polymers (DAMN is the formal tetramer of the HCN), which currently present a growing interest in materials science. Recently, the thermal polymerizability of DAMN has been reported, both in an aqueous medium and in bulk, offering the potential for the development of capacitors and biosensors, respectively. In the present work, the polymerization of this plausible prebiotic molecule has been hydrothermally explored using microwave radiation (MWR) via the heating of aqueous DAMN suspensions at 170–190 °C. In this way, polymeric submicron particles derived from DAMN were obtained for the first time. The structural, thermal decomposition, and electrochemical properties were also deeply evaluated. The redox behavior was characterized from DMSO solutions of these highly conjugated macromolecular systems and their potential as semiconductors was described. As a result, new semiconducting polymeric submicron particles were synthetized using a very fast, easy, highly robust, and green-solvent process. These results show a new example of the great potential of the polymerization assisted by MWR associated with the HCN-derived polymers, which has a dual interest both in chemical evolution and as functional materials.
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Solid-state polymerization of diaminomaleonitrile: Toward a new generation of conjugated functional materials
(Elsevier BV, 2021-05-03) Hortelano, C.; Ruiz Bermejo, Marta; De la Fuente, J. L.; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
The solid-state polymerization (SSP) of organic molecules to form two-dimensional (2D) materials remains a challenge, especially when these reactions are performed in one pot using a single reagent. As will be shown, the SSP of the HCN tetramer diaminomaleonitrile (DAMN) may be an excellent example of these reactions. Dynamic experiments by differential scanning calorimetry (DSC) allow the analysis of the thermally initiated bulk polymerization of DAMN. Under nonisothermal measurements at low heating rates, a multiple-step polymerization reaction takes place. The SSP of DAMN is highly efficient, possibly due to the autocatalytic nature of its kinetics, which are consistent with the two-parameter Šesták-Berggren (SB) model and describe the three stages found in its complicated mechanism, confirmed also from an analysis of the variation in the apparent activation energy with the conversion degree. Relevant mechanistic aspects, such as the dehydrocyanation and deamination processes during SSP, are extracted by thermogravimetry-mass spectrometry (TG-MS). Moreover, some structural and morphological properties of these materials are characterized by Fourier-transform infrared (FTIR) spectroscopy and microscopy. All this information allows us to propose hypothetical pathways for the production of a complex conjugated system, predominantly constituted by a 2D macrostructure based on imidazole rings. This work opens up new possibilities for the synthesis of functional poly(heterocycle) systems, expanding our view of a plausible prebiotic chemical reaction space and providing the foundation for systematic studies of the structure-property relationships of novel HCN-derived polymers, which are currently of great interest in the fields of materials and surface science.
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Temperature effect on aqueous NH4CN polymerization: Relationship between kinetic behaviour and structural properties
(Elsevier BV, 2020-06-05) Mas, I.; De la Fuente, J. L.; Ruiz Bermejo, Marta; Agencia Estatal de Investigación (AEI); De la Fuente, J. L. [https://orcid.org/0000-0002-1855-0153]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Herein, a kinetic analysis for aqueous NH4CN polymerizations is presented, which is consistent with an autocatalytic model when polymerizations are performed at relatively high temperatures, 80–90 °C. Further experiments at lower polymerization temperatures, approximately 50 °C, have demonstrated that this relevant prebiotic reaction follows nth-order kinetics rather than an autocatalytic mechanism. In addition, the sol fractions of these precipitation polymerizations have been evaluated by UV–Vis measurements, which also show a mechanistic shift with the reaction temperature. This change in the kinetic behaviour led to the proposal of a simple empirical methodology to describe both chemical- and diffusion-controlled regions. Despite the simplicity of the approach based on the Hill equation, fundamental kinetic parameters, such as the activation energy, can be determined in the diffusion-free zone. These results motivated a systematic structural characterization study of the respective insoluble polymers by means of elemental analysis, FT-IR and NMR spectroscopies and XRD. All these kinetic and structural analyses confirmed that the temperature has a significant effect on the polymerization kinetic of the system, on the macrostructural features and properties of the HCN-based polymers, and presumably also on the polymerization pathways. These data increase our knowledge about the chemistry of this particular family of HCN polymers, which is currently of interest both in the field of materials science and in prebiotic chemistry and astrobiology.
Acceso Abierto
Tuning the Morphology in the Nanoscale of NH4CN Polymers Synthesized by Microwave Radiation: A Comparative Study
(Multidisciplinary Digital Publishing Institute (MDPI), 2021-12-24) Pérez Fernández, Cristina; Valles González, M. P.; González Toril, Elena; Mateo Martí, Eva; De la Fuente, J. L.; Ruiz Bermejo, Marta; Instituto Nacional de Técnica Aeroespacial (INTA); Ministerio de Ciencia e Innovación (MICINN); Agencia Estatal de Investigación (AEI); Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
A systematic study is presented to explore the NH4CN polymerization induced by microwave (MW) radiation, keeping in mind the recent growing interest in these polymers in material science. Thus, a first approach through two series, varying the reaction times and the temperatures between 130 and 205 °C, was conducted. As a relevant outcome, using particular reaction conditions, polymer conversions similar to those obtained by means of conventional thermal methods were achieved, with the advantage of a very significant reduction of the reaction times. The structural properties of the end products were evaluated using compositional data, spectroscopic measurements, simultaneous thermal analysis (STA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). As a result, based on the principal component analysis (PCA) from the main experimental results collected, practically only the crystallographic features and the morphologies in the nanoscale were affected by the MW-driven polymerization conditions with respect to those obtained by classical syntheses. Therefore, MW radiation allows us to tune the morphology, size and shape of the particles from the bidimensional C=N networks which are characteristic of the NH4CN polymers by an easy, fast, low-cost and green-solvent production. These new insights make these macromolecular systems attractive for exploration in current soft-matter science.