Burning-rate enhancement of a high-energy rocket composite solid propellant based on ferrocene-grafted hydroxyl-terminated polybutadiene binder

Research progress of EMOFs-based burning rate catalysts for solid propellants

Energetic Metal Organic Frameworks (EMOFs) have been a hotspot of research on solid propellants in recent years. In this paper, research on the application of EMOFs-based burning rate catalysts in solid propellants was reviewed and the development trend of these catalysts was explored. The catalysts analyzed included monometallic organic frameworks-based energetic burning rate catalysts, bimetallic multifunctional energetic burning rate catalysts, carbon-supported EMOFs burning rate catalysts, and catalysts that can be used in conjunction with EMOFs. The review suggest that monometallic organic frameworks-based burning rate catalysts have relatively simple catalytic effects, and adding metal salts can improve their catalytic effect. Bimetallic multifunctional energetic burning rate catalysts have excellent catalytic performance and the potential for broad application. The investigation of carbon-supported EMOFs burning rate catalysts is still at a preliminary stage, but their preparation and application have become a research focus in the burning rate catalyst field. The application of catalysts that can be compounded with EMOFs should be promoted. Finally, environmental protection, high energy and low sensitivity, nanometerization, multifunctional compounding and solvent-free are proposed as key directions of future research. This study aims to provide a reference for the application of energetic organic burning rate catalysts in solid propellants.

Catalytic Effect of Ferrocenyl Energetic Catalysts for N-Guanylurea Dinitramide (GUDN or FOX-12) Decomposition

Four N,N-dimethylaminomethylferrocene polynitrogen catalysts were applied to the thermal decomposition of FOX-12, and their catalytic effect on FOX-12 was investigated by TG-DSC. The kinetic parameters and kinetic model of the mixed system were revealed by the Kissinger method, Freidman method, and combined kinetic analysis. The results showed that MAFcTAZ is the catalyst with the strongest effect on FOX-12, the decomposition peak temperature of FOX-12 is reduced, and the decomposition weight loss is higher than those for other catalysts, which prove that the decomposition of FOX-12 is more thorough under the catalysis of MAFcTAZ. The introduction of the four catalysts reduced the thermal decomposition peak temperature of FOX-12. MAFcTAZ was the most active catalyst for the decomposition of FOX-12, and the maximum heat release of catalyzing the decomposition of FOX-12 can reach 1236.76 J·g^-1. The activation energy (E _a) of FOX-12 decomposition decreased from 217.91 to 128.19, 137.85, 157.65, and 151.91 kJ·mol^-1 under the effect of MAFcNO₃, MAFcPA, MAFcNTO, and MAFcTAZ. The Freidman analysis illustrated that MAFcTAZ reduced the activation energy during the entire decomposition process of FOX-12. The physical model of the decomposition reaction of FOX-12 transformed from the random nucleation and two-dimensional growth of nuclei model (A2) to the random scission model (L2) in the presence of MAFcNO₃ and two-dimensional diffusion (D2) under the effect of MAFcPA, MAFcNTO, and MAFcTAZ. By analyzing the molecular structures, MAFcTAZ has a higher iron content and nitrogen content, which are the essence of its excellent catalytic performance. From the perspective of interaction energy, the strong catalytic effect of MAFcTAZ is attributed to its large interaction energy with FOX-12 by energy decomposition analysis.

Glycidyl azide polymer-based polyurethane vitrimers with disulfide chain extenders

Glycidyl azide polymer-based polyurethane vitrimers were synthesized. By optimizing the parameters, the vitrimers showed decent mechanical properties, healability and reprocessability. Fillers were loaded to synthesize healable composites.

8-Aminoquinoline-Assisted Synthesis and Crystal Structure Studies of Ferrocenyl Aryl Sulfones

A copper-catalyzed 8-aminoquinoline-directed oxidative cross-coupling of the C-H bond of ferrocene with sodium arylsulfinates has been achieved. The robust copper catalyst tolerates a range of methyl, tert-butyl, bromo, chloro, iodo and nitro functional groups in the phenyl ring, and set the stage for the synthesis of substituted ferrocene sulfones. Furthermore, X-ray crystal structure study on several ferrocenyl sulfones reveals the tetrahedral geometry around sulfur; interestingly, the O-S-O angle is larger than the electropositive substituent C-S-C angle which could be explained by Bent's rule. Further, unusual intramolecular O(S)⋅⋅⋅N(amide) short contacts (2.925-3) and O(S)⋅⋅⋅C=O were also noticed in ferrocenyl sulfones.

Study on the thermal decomposition mechanism of graphene oxide functionalized with triaminoguanidine (GO-TAG) by molecular reactive dynamics and experiments

Graphene oxide (GO) has a catalytic effect on the thermal decomposition of energetic materials above the melting point. To further enhance the catalytic activity of GO, it has been functionalized with the high nitrogen ligand triaminoguanidine (TAG). However, theoretical studies on the reactivity of functionalized GO (e.g., GO-TAG) have not been carried out. Therefore, the thermal decomposition of each TAG, GO and GO-TAG is studied by molecular dynamic simulations using a reactive force-field (ReaxFF) with experimental verification, and the results are reported herein. The results show that the GO nanolayer has a tendency to aggregate into a large carbon cluster during its degradation. The main decomposition products of TAG are NH₃, N₂ and H₂. For GO-TAG, the main decomposition products are H₂O, NH₃, N₂ and H₂. GO has a significant acceleration effect on the decomposition process of TAG by decreasing the decomposition temperature of TAG. This phenomenon is in agreement with the experimental results. The initial decomposition of TAG is mainly caused by hydrogen transfer in the molecule. The edge carbon atoms of GO promote the decomposition of TAG molecules and reduce the decomposition activation energy of TAG by 15.4 kJ mol⁻¹. Therefore, TAG will quickly decompose due to the catalytic effect of GO. This process produces a “new” GO that catalyzes the decomposition of components such as TAG. At the same time, many free radicals (HN₂, H₂N and free H) are generated during the decomposition of TAG to catalyze the decomposition of other components, which in turn, enhance the catalytic capability of GO.

The edge carbon atoms on the GO promote the decomposition of TAG.

Effect of Solvent and Functionality on the Physical Properties of Hydroxyl-Terminated Polybutadiene (HTPB)-Based Polyurethane

The present article reports the investigation on the effects of solvent and position of functionality on various physical properties of polyurethanes (PUs) based on hydroxyl-terminated polybutadiene (HTPB). The PU films (curative)  were prepared by coupling HTPB (P0) with isophorone diisocyanate (IPDI) in various solvent media. The PUs obtained in different solvent media displayed similar thermal profile and glass transition temperature (T _g), but their tensile properties varied significantly. Optimized tensile properties were observed when tetrahydrofuran was used as the solvent media. In the course, the investigation of the functionality effect, tetrazole (M1, M2, and M3) were covalently attached at the terminal carbon of HTPB to obtain three modified HTPBs (P1, P2, and P3), thereby coupling with IPDI to obtain the corresponding tetrazole functional PUs films. Pristine (P0-PU) and functional PU (P1-PU, P2-PU, and P3-PU) films have similar thermal profile and T _g (-76 °C), but they have a notable enhancement in tensile properties; for example, tensile strength and elongation at break of P0-PU were found to be 3.21 MPa and 727%, respectively, whereas these values were 4.84 MPa and 958%, respectively, in the case of P3-PU. It was observed that on increasing the number of methylene group from 1 to 3 between HTPB and tetrazole moiety, the strength of hydrogen bonding increases, which facilitates better packing of urethane network in the PU and hence improves the tensile properties. Also, modification of pristine HTPB with tetrazole derivatives enhanced the calorific values of the resulting PUs.

Anti-migration and burning rate catalytic performances of novel ferrocene-based porphyrins and their transition-metal complexes

Novel ferrocene-based porphyrins and metal porphyrins exhibited non-migratory ability and excellent burning rate catalytic performance for composite solid propellants.

Effects of electrochemical properties of ferrocenylpyrazolylnickel(ii) and palladium(ii) compounds on their catalytic activities in ethylene oligomerisation reactions

Palladium complexes of ferrocenylpyrazolylpyridine and ferrocenylpyrazolylamine were synthesised and screened as pre-catalysts (1–4) for olefin polymerisation. The pre-catalysts 1–4 on activation with EtAlCl₂ in the presence of ethylene with chlorobenzene or hexane as solvent were highly active with 1 being the most active, with an activity of 360 kg mol Pd⁻¹ h⁻¹. The major product from the reaction was 1-butene and high carbon content oligomers. The molecular weight (m/z) of the high carbon content oligomers is as high as 623.0. When toluene is used as solvent, the products obtained were ethyltoluene and butyltoluene and 1-butene. The electronic properties of the ligands (L1–L7) and complexes (1–10) were determined by cyclic voltammetry (CV) and molecular modelling. The CV results show that the ferrocenyl is easily oxidized upon the introduction of pyrazolyl derivatives, the process is quasi-reversible. However, complexation of the ligands with palladium or nickel results in difficulty in oxidizing the ferrocenyl moiety. This is an indication of the electrophilic nature of both the palladium and nickel centres. The mechanism of the oxidation was observed to be diffusion-controlled and is independent of scan rate. Molecular modelling experiments show that nickel and palladium complexes have lower HOMO–LUMO gaps and high global descriptors, an indication of a highly electrophilic metal centre. A plot of the electrophilicity indices of the pre-catalysts against yield of the oligomers show a linear correlation, an indication that the electrophilicity of the metal centre plays an important role in the activity of these pre-catalysts.

Studying the correlation between the electrophilicity of the metal centre and the activity of the resulting catalyst using electrochemistry and computation modelling.

N-alkyl-2-(1,2-diferrocenylvinyl)-4,5-dihydrooxazolinium salts, multi-component synthesis and breaking of their heterocyclic systems

A new multicomponent method for the synthesis of N-alkyl-2-(Z-1,2-diferrocenylvinyl)-4,5-dihydrooxazolinium salts 3a–f, 5-(N-alkyl-2′,3′-diferrocenyl-acryloylamido)-3-aza-3-alkylpentanols 4a–d, (E)-N-alkyl-N-(2-morpholinoethyl)-2,3-diferrocenylacrylamides 9a,b,e,f and (E)-N-alkyl-N-(2-piperidinoethyl)-2,3-diferrocenylacrylamides 10a,c from reactions of 2,3-diferrocenylcyclopropenone 1 with bis-1,4-N,O-nucleophiles in the presence of triethyloxonium tetrafluoroborate, alkyl iodides, morpholine, piperidine and Et3N is described. The characterization of the new compounds was done by IR, 1H- and 13C-NMR spectroscopy, mass-spectrometry, elemental analysis and X-ray diffraction studies.

Synthesis of ferrocene-based saccharides and their anti-migration and burning rate catalytic properties

In the search for ferrocene-based burning rate catalysts (BRCs) with good burning rate catalytic properties and low migration, we synthesized four ferrocene-based saccharides (S-Fcs).

Ferrocene and [3]ferrocenophane-based β-diketonato copper(ii) and zinc(ii) complexes: synthesis, crystal structure, electrochemistry and catalytic effect on thermal decomposition of ammonium perchlorate

Ferrocene and [3]ferrocenophane-based β-diketonato Cu(ii) complexes exhibit enhanced electrochemical behaviors and burning rate catalytic effects compared with the Zn(ii) complexes.

Effects of metal organic framework Fe-BTC on the thermal decomposition of ammonium perchlorate

Fe-BTC effectively enhances the thermal decomposition of AP and improves the combustion properties of BAMO–THF propellant with AP as the oxidizer.