Imide Systems Research Articles

Ab initio thermochemistry study of polymorphism in the Si2N2(NH) analog of Si2N2O

We present a systematic density functional theory (DFT) study of the structural, bonding and electronic properties of the Si2N2(NH) polymorphs. This recently synthesized compound is a direct analog of Si2N2O in which the oxygen is replaced by an NH group. We show that a local-density approximation (LDA) description in the static lattice approximation gives a good account of the lowest energy orthorhombic phase of both the parent oxide and imide analog. In this work we extend our systematic comparisons between Si2N2O and Si2N2(NH) to denser tetragonal and monoclinic polymorphs. For Si2N2(NH) we find that the tetragonal and monoclinic polymorphs have energies 0.8 and 1.8 eV higher than (respectively) that of the orthorhombic ground state, similar to their Si2N2O counterparts (0.6 and 1.4 eV, respectively). We elucidate differences in chemical binding in Si2N2O and Si2N2(NH) polymorphs using Bader charge analysis and conclude that the imide systems possess slightly less ionic character than their oxide counterpart. Using the modified Becke-Johnson (MBJ) meta-LDA approach we find that orthorhombic Si2N2O and Si2N2NH have direct gaps of 5.65 and 5.75 eV, respectively, in excellent agreement with experiment. Relative to the orthorhombic Si2N2O (5.65 eV, direct), the band gaps in the denser polymorphs increase and become indirect (tetragonal: 5.72 eV, monoclinic: 6.06 eV). We find more complex trends in Si2N2NH in which the band gaps are also indirect in character, but decrease to 3.91 eV in the tetragonal phase, and then increase to 4.18 eV (Γ → D) in the monoclinic case.

Recent Progress and New Perspectives on Metal Amide and Imide Systems for Solid-State Hydrogen Storage

Hydrogen storage in the solid state represents one of the most attractive and challenging ways to supply hydrogen to a proton exchange membrane (PEM) fuel cell. Although in the last 15 years a large variety of material systems have been identified as possible candidates for storing hydrogen, further efforts have to be made in the development of systems which meet the strict targets of the Fuel Cells and Hydrogen Joint Undertaking (FCH JU) and U.S. Department of Energy (DOE). Recent projections indicate that a system possessing: (i) an ideal enthalpy in the range of 20–50 kJ/mol H2, to use the heat produced by PEM fuel cell for providing the energy necessary for desorption; (ii) a gravimetric hydrogen density of 5 wt. % H2 and (iii) fast sorption kinetics below 110 °C is strongly recommended. Among the known hydrogen storage materials, amide and imide-based mixtures represent the most promising class of compounds for on-board applications; however, some barriers still have to be overcome before considering this class of material mature for real applications. In this review, the most relevant progresses made in the recent years as well as the kinetic and thermodynamic properties, experimentally measured for the most promising systems, are reported and properly discussed.

Lithium imide systems for high temperature heat storage in concentrated solar thermal systems

Hydrogen is touted as one of the solutions for future energy requirements. Metal hydrides typically studied for their high hydrogen capacity can be used as a thermal storage system by taking advantage of their endothermic/exothermic reactions with hydrogen. This allows the harnessing of solar energy by utilising thermal storage to alleviate its intermittent nature. Lithium amide (LiNH2), imides (Li2NH) and nitrides (Li3N) have been widely studied for their hydrogen storage at relatively low operating temperatures, typically suited for mobile applications. However, little work has been done involving the imide to nitride reaction of lithium-based materials due to their high temperature range. The following techniques were used to characterise this system: temperature programmed desorption (TPD), temperature programmed photographic analysis (TPPA), x-ray diffraction (XRD) and pressure-composition-temperature (PCT) measurements. TPD results revealed that only a single-step reaction occurred between 100 and 600 °C. TPPA revealed that having a molten solid solution of the sample, depreciated the reversibility of hydrogen absorption and desorption. The molten sample behaved quite vigorously in TPPA measurements and consequently blocked sample filters and sintering sample cell walls; creating engineering problems at higher temperatures. The results revealed that for reactions involving Li2NH and lithium hydride (LiH), the temperature range required for thermal storage is above the melting point of the system. The diffusion and absorption of hydrogen through stainless steel would also occur in the sample cells used, resulting in further problems. The reaction pathway of Li2NH and LiH was also found to be far more complex than generally reported: XRD revealed that the expected final product of Li3N could not be identified, instead a lithium imide-nitride hydride phase (Li4‑2xN1‑xH1‑x(NH)x) was identified as the final product of this system. PCT measurements were conducted to identify the kinetic and thermodynamics of this system, but because of the molten solid-solution problem, an accurate result could not be obtained.

Two-Peak Mystery of LiNH2–NaH Dehydrogenation Is Solved? A Study of the Analogous Sodium Amide/Lithium Hydride System

Alkali metal amide and imide systems especially NaNH2 and Li2NH have recently been proposed as a catalyst for NH3 cracking. This finding ignites the interest of researchers worldwide to study amide–imide/amide–hydride systems. Although these systems have shown catalytic properties toward NH3 cracking and have also been proposed as a hydrogen storage material, the decomposition mechanism of sodium amide is still unclear due to the complexity and low melting point of NaNH2. Herein, pure NaNH2 and its composite with lithium hydride as well as sodium hydride in a molar ratio 1:1 has been investigated, and a detailed mechanism associated with their decomposition has been suggested. The sodium amide–lithium hydride system is found to be analogous to lithium amide–sodium hydride. It desorbs 4 wt % H2 through cation exchange in a temperature range of 25–200 °C followed by NH3 mediated reaction in the temperature range 200–400 °C. The desorbed product can be rehydrogenated at around 200 °C under 2.0 MPa. An import...

Development of novel cardo-containing phenylethynyl-terminated polyimide with high thermal properties

A phenylethynyl-terminated reactive diluent [Card-4-phenylethynylphthalic anhydride (PEPA)], which contained fluorenyl cardo structures, was successfully synthesized and used as a modifier for flexible phenylethynyl-terminated imide oligomer (PEI-PEPA). The chemical structure, crosslink characterization, molecular weights, and thermal properties of the products were characterized. The imide systems with addition of 10, 20, 30, and 40 wt% Card-PEPA to PEI-PEPA (PEI-PEPA-Card) and their cured resin systems were prepared. The thermal curing behaviors of imide systems at different heating rates were analyzed by using differential scanning calorimetry. Thermal properties such as glass transition temperature (Tg) and char yield at 800°C of the resultant resin systems were studied by differential scanning calorimetry, dynamic mechanical analysis, and thermogravimetric analysis. The rheological properties were also investigated using a dynamic rheometry. These properties were found to be outstanding compared with pure PEI-PEPA. The uncured imide systems exhibited lower Tg and lower isothermal viscosity with addition of Card-PEPA. Furthermore, the Tg and char yield of the cured resin systems increased with addition of Card-PEPA. The cured resin systems containing 40 wt% Card-PEPA exhibited the highest Tg of 359°C and char yield at 800°C of 66.5%. Copyright © 2016 John Wiley & Sons, Ltd.

Thermal degradation behavior of carborane-containing phenylethynyl terminated imide systems

Carborane-containing imide compound (Carb-PEPA) was synthesized and added into fluorinated phenylethynyl terminated imide oligomer (AFR-PEPA). The thermal degradation of Carb-PEPA was studied by thermogravimetric analyzer coupled with Fourier transform infrared analysis (TG-FTIR), in situ FTIR and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS). The results show that the Carb-PEPA possesses high char yield in both air and nitrogen due to the formation of BO bonds in thermal degradation process as identified by TG-FTIR and in situ FTIR. A thermal degradation mechanism for the Carb-PEPA was proposed. The Carb-PEPA crosslinks to form polyimide in the early heating process. Then the degradation of Carb-PEPA happens at higher temperatures, while further degradation could be effectively prevented due to the formation of a protection layer of boron oxide compound. The thermal stabilities of AFR-PEPA and AFR-PEPA containing 15 wt% Carb-PEPA (AFR-PEPA-Carb-15) were also studied by TGA and TG-FTIR. It was observed that AFR-PEPA’s residual weight ratios at 800 °C in air and nitrogen increased by 20% and 13.3% respectively with the addition of 15 wt% Carb-PEPA.

The New Fluorescent Naphthalic Imide Derivatives Having the Inductive Ending Group

the new naphthalic imide systems were synthesized systema-tically and their photophysical properties were studied. We found for the first time that the new imide systems showed a considerable emission regardless of having the electron with-drawing group in the imide systems. Herein, we report the emission results on the new naphthalic imide systems having electron donating group (X = CH

Asymmetric radical carboncarbon bond forming reactions in chiral amides and imides under sulfonyl groups stereocontrol

Asymmetric radical carbon–carbon bond formation was achieved in chiral amide and imide systems under sulfonyl group stereocontrol, providing high diastereoselectivity. The stereochemistry of the products was determined and the mechanism of the stereochemical pathways is rationalized by the formation of chelates of Lewis acid metals between oxygens of acetyl, amide, and imide carbonyls, or sulfonyl groups.

An Update to the Combined Vibrational- Diffraction Experimental and Theoretical Studies of Small Biologically Important Cyclic Imides:Reference to Saccharin

The small-sized cyclic imides and amides have been for a long time known as convenient models for study of numerous biochemical processes. In addition, owing to the structural resemblance with their naturally occurring analogues, biological activity has been documented for a number of these compounds. Recent development of the experimental and especially high-level theoretical structural methods has provided new evidences for their structure and properties. The present review aims to summarize the vibrational, structural and combined data published during the last decade on selected five- and six-membered ring imides and derivatives thereof, in the attempt to update the existing knowledge for this class of compounds. As an exceptionally suitable and thoroughly studied model system that has also been a subject for research to the authors for quite some time, the vibrational-structural results for sulfobenzimide (saccharin) and its compounds are also reviewed. The inferences are designed to be applied to other, less-studied imide systems. In spite of the recent vast progress of the analytical methods, simultaneous use of vibrational and diffraction experimental/theoretical results has proven to be far more reliable for better structural interpretation than any of these alone.

Epoxy–imide resins from N‐(4‐ and 3‐carboxyphenyl)trimellitimides. I. Adhesive and thermal properties

Epoxy–imide resins were obtained by curing Araldite GY 250 (diglycidyl ether of bisphenol-A and epichlorohydrin; difunctional) and Araldite EPN 1138 (Novolac–epoxy resin; polyfunctional) with N-(4- and 3-carboxyphenyl)trimellitimides derived from 4- and 3-aminobenzoic acids and trimellitic anhydride. The adhesive lap shear strength of epoxy–imide systems at room temperature and at 100, 125, and 150°C was determined on stainless-steel substrates. Araldite GY 250-based systems give a room-temperature adhesive lap shear strength of about 23 MPa and 49–56% of the room-temperature adhesive strength is retained at 150°C. Araldite EPN 1138-based systems give a room-temperature adhesive lap shear strength of 16–19 MPa and 100% retention of room-temperature adhesive strength is observed at 150°C. Glass transition temperatures of the Araldite GY 250-based systems are in the range of 132–139°C and those of the Araldite EPN 1138-based systems are in the range of 158–170°C. All these systems are thermally stable up to 360°C. The char residues of Araldite GY 250- and Araldite EPN 1138-based systems are in the range of 22–26% and 41–42% at 900°C, respectively. Araldite EPN 1138-based systems show a higher retention of adhesive strength at 150°C and have higher thermal stability and Tg when compared to Araldite GY 250-based systems. This has been attributed to the high crosslinking possible with Araldite EPN 1138-based systems arising due to the polyfunctional nature of Araldite EPN 1138. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1729–1736, 2000

Solid state lithium ion conduction in pyrrolidinium imide–lithium imide salt mixtures

The properties of the binary salt system based on mixtures of methyl ethyl pyrrolidinium bis(trifluoromethane sulfonyl) imide (P 12) and lithium bis(trifluoromethane sulfonyl) imide (Li imide) are reported. The lithium containing mixtures were found to be more than two orders of magnitude more conductive than the parent P 12 phase and the 33 mol% Li imide systems showed a solid state conductivity around 1×10 −4 S/cm at 20°C. This solid state conductivity is believed to take place in plastic crystal phases of the P 12 compound.

Epoxy-imide resins from N-(4- and 3-carboxyphenyl)trimellitimides. I. Adhesive and thermal properties

Epoxy–imide resins were obtained by curing Araldite GY 250 (diglycidyl ether of bisphenol-A and epichlorohydrin; difunctional) and Araldite EPN 1138 (Novolac–epoxy resin; polyfunctional) with N-(4- and 3-carboxyphenyl)trimellitimides derived from 4- and 3-aminobenzoic acids and trimellitic anhydride. The adhesive lap shear strength of epoxy–imide systems at room temperature and at 100, 125, and 150°C was determined on stainless-steel substrates. Araldite GY 250-based systems give a room-temperature adhesive lap shear strength of about 23 MPa and 49–56% of the room-temperature adhesive strength is retained at 150°C. Araldite EPN 1138-based systems give a room-temperature adhesive lap shear strength of 16–19 MPa and 100% retention of room-temperature adhesive strength is observed at 150°C. Glass transition temperatures of the Araldite GY 250-based systems are in the range of 132–139°C and those of the Araldite EPN 1138-based systems are in the range of 158–170°C. All these systems are thermally stable up to 360°C. The char residues of Araldite GY 250- and Araldite EPN 1138-based systems are in the range of 22–26% and 41–42% at 900°C, respectively. Araldite EPN 1138-based systems show a higher retention of adhesive strength at 150°C and have higher thermal stability and Tg when compared to Araldite GY 250-based systems. This has been attributed to the high crosslinking possible with Araldite EPN 1138-based systems arising due to the polyfunctional nature of Araldite EPN 1138. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1729–1736, 2000