Polymers with Circularly Polarized Luminescent Properties: Design, Synthesis, and Prospects.

Chiral materials with circularly polarized luminescence (CPL) have garnered significant attention owing to their distinctive luminescent properties and wide array of applications. CPL enables the selective emission of left and right circularly polarized light. The fluorescence quantum yield and dissymmetry factor play pivotal roles in the generation of CPL. Helical polymers exhibit immense promise as CPL materials due to their inherent chirality, structural versatility, modifiability, and capacity to incorporate diverse chromophores. This Review provides a brief review of the synthesis of CPL materials based on helical polymers. The CPL can be realized by aggregation-induced CPL of non-emissive helical polymers, and helices bearing chromophores on the pendants and on the chain end. Furthermore, future challenges and potential applications of CPL materials are summarized and discussed.

Controlled synthesis of cyclic helical polyisocyanides and bottlebrush polymers using a cyclic alkyne-Pd(II) catalyst.

Cyclic polymers have very unique structure and properties, and thus have drawn intense research attention. However, controlled synthesis of cyclic polymers with predictable molar mass and narrow distribution is still a challenging task. In this study, we developed a novel cyclic catalyst that initiates the ring-expansion polymerisation of isocyanides, producing a series of cyclic helical polymers with predictable molecular weight and low dispersity. Interestingly, the ring-expansion polymerization of the isocyanide macromonomers gives well-defined cyclic bottlebrush polymers. The cyclic topology was demonstrated using transmission electron microscopy.

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.

Fabrication of CL-20/HMX Cocrystal@Melamine-Formaldehyde Resin Core-Shell Composites Featuring Enhanced Thermal and Safety Performance via In Situ Polymerization.

Safety concerns remain a bottleneck for the application of 2,4,6,8,10,12-hexanitro- 2,4,6,8,10,12-hexaazaisowurtzitane (CL-20)/1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX) cocrystal. Melamine-formaldehyde (MF) resin was chosen to fabricate CL-20/HMX cocrystal-based core-shell composites (CH@MF composites) via a facile in situ polymerization method. The resulted CH@MF composites were comprehensively characterized, and a compact core-shell structure was confirmed. The effects of the shell content on the properties of the composites were explored as well. As a result, we found that, except for CH@MF-2 with a 1% shell content, the increase in shell content led to a rougher surface morphology and more close-packed structure. The thermal decomposition peak temperature improved by 5.3 °C for the cocrystal enabled in 1.0 wt% MF resin. Regarding the sensitivity, the CH@MF composites exhibited a significantly reduced impact and friction sensitivity with negligible energy loss compared with the raw cocrystal and physical mixtures due to the cushioning and insulation effects of the MF coating. The formation mechanism of the core-shell micro-composites was further clarified. Overall, this work provides a green, facile and industrially potential strategy for the desensitization of energetic cocrystals. The CH@MF composites with high thermal stability and low sensitivity are promising to be applied in propellants and polymer-bonded explosive (PBX) formulations.

Facile synthesis and superior properties of a nitrogen-rich energetic Zn-MOF with a 2D azide-bridged bilayer structure.

Exploring the facile synthesis of Pb-free energetic metal-organic frameworks (EMOFs) with both high nitrogen content and high thermostability is a significant but challenging task in the field of MOF-based green energetic materials. Herein, a new EMOF, [Zn2(atz)3(N3)]n (atz = 5-amino-1H-tetrazole), has been synthesized by simply using a commercial ligand (atz) under mild conditions. A probable mechanism for the formation of azide groups in the product has been proposed, in which the fraction of C-N and N-N bonds in atz is the key. The X-ray single crystal structure analysis reveals the EMOF's unique graphene-like and azide-group-bridged 2D bilayer structure with gourd-type micropores. More impressively, the EMOF shows a high nitrogen content of 59.33% and superior thermostability of up to 362 °C, both among the best of existing EMOFs. In addition, detonation property calculations and sensitivity tests have been carried out, which demonstrate its high-energy and low-sensitivity features. Moreover, [Zn2(atz)3(N3)]n shows the ability to accelerate the thermal decomposition of ammonium perchlorate (AP) and hexanitrohexaazaisowurtzitane (CL-20), making it a potential combustion promoter for green and insensitive propellants.

The Art of Framework Construction: Core-Shell Structured Micro-Energetic Materials.

Weak interfacial interactions remain a bottleneck for composite materials due to their weakened performance and restricted applications. The development of core-shell engineering shed light on the preparation of compact and intact composites with improved interfacial interactions. This review addresses how core-shell engineering has been applied to energetic materials, with emphasis upon how micro-energetic materials, the most widely used particles in the military field, can be generated in a rational way. The preparation methods of core-shell structured explosives (CSEs) developed in the past few decades are summarized herein. Case studies on polymer-, explosive- and novel materials-based CSEs are presented in terms of their compositions and physical properties (e.g., thermal stability, mechanical properties and sensitivity). The mechanisms behind the dramatic and divergent properties of CSEs are also clarified. A glimpse of the future in this area is given to show the potential for CSEs and some suggestions regarding the future research directions are proposed.

Selective reduction of nitrite to nitrogen gas by CO2 anion radical from the activation of oxalate.

Nitrite (NO2-) reduction by carbon dioxide anion radical (CO2•-) from the activation of small molecule carboxylic acid was investigated to selectively reduce nitrite to nitrogen gas (N2). However, the CO2•- generation efficiency from the activation of small molecule carboxylic acid needs to be enhanced to increase the NO2- reduction efficiency. In this study, a novel and promising process for selective NO2- reduction was proposed based on activation of oxalic acid (OA) by UV radiation coupled with Fe3+. In Fe(III)/OA/UV system, the activation of OA by photo-induced electron transfer process of Fe(III)-oxalate complex and by •OH radical from the photolysis of Fe3+ or NO2- could promote the generation of CO2•- radical, which enhanced the NO2- reduction. The 100% removal efficiency of NO2-, 94.72% of total nitrogen (TN) and 94.72% of selectivity for N2 were achieved in Fe(III)/OA/UV/NO2- system, at the Fe3+ dosage of 8 mmol/L, initial pH of 1.70, OA dosage of 16 mmol/L, initial NO2- concentration of 30 mg N/L, and reaction time of 180 min. CO2•- radical played a significant role in the reduction of NO2- by Fe(III)/OA/UV system based on the inhibition experiments in which methyl violet was used as a quenching agent of CO2•- radical. Based on the results from batch experiments and FTIR analysis, the activation mechanism of OA and selective reduction mechanism of NO2- in Fe(III)/OA/UV system was proposed.

Screening for energetic compounds based on 1,3-dinitrohexahydropyrimidine skeleton and 5-various explosopheres: molecular design and computational study.

In this paper, twelve 1,3-dinitrohexahydropyrimidine-based energetic compounds were designed by introducing various explosopheres into hexahydropyrimidine skeleton. Their geometric and electronic structures, heats of formation (HOFs), energetic performance, thermal stability and impact sensitivity were discussed. It is found that the incorporation of electron-withdrawing groups (-NO2, -NHNO2, -N3, -CH(NO2)2, -CF(NO2)2, -C(NO2)3) improves HOFs of the derivatives and all the substituents contribute to enhancing the densities and detonation properties (D, P) of the title compounds. Therein, the substitution of -C(NO2)3 features the best energetic performance with detonation velocity of 9.40 km s-1 and detonation pressure of 40.20 GPa. An analysis of the bond dissociation energies suggests that N-NO2 bond may be the initial site in the thermal decompositions for most of the derivatives. Besides, -ONO2 and -NF2 derivatives stand out with lower impact sensitivity. Characters with striking detonation properties (D = 8.62 km s-1, P = 35.08 GPa; D = 8.81 km s-1, P = 34.88 GPa), good thermal stability, and acceptable impact sensitivity (characteristic height H50 over 34 cm) lead novel compounds 5,5-difluoramine-1,3-dinitrohexahydropyrimidine (K) and 5-fluoro-1,3,5-trinitrohexahydropyrimidine (L) to be very promising energetic materials. This work provides the theoretical molecular design and a reasonable synthetic route of L for further experimental synthesis and testing.

Comparative Theoretical Studies on a Series of Novel Energetic Salts Composed of 4,8-Dihydrodifurazano[3,4-b,e]pyrazine-based Anions and Ammonium-based Cations.

4,8-Dihydrodifurazano[3,4-b,e]pyrazine (DFP) is one kind of parent compound for the synthesis of various promising difurazanopyrazine derivatives. In this paper, eleven series of energetic salts composed of 4,8-dihydrodifurazano[3,4-b,e]pyrazine-based anions and ammonium-based cations were designed. Their densities, heats of formation, energetic properties, impact sensitivity, and thermodynamics of formation were studied and compared based on density functional theory and volume-based thermodynamics method. Results show that ammonium and hydroxylammonium salts exhibit higher densities and more excellent detonation performance than guanidinium and triaminoguanidinium salts. Therein, the substitution with electron-withdrawing groups (-NO2, -CH2NF2, -CH2ONO2, -C(NO2)3, -CH2N3) contributes to enhancing the densities, heats of formation, and detonation properties of the title salts, and the substitution of -C(NO2)3 features the best performance. Incorporating N-O oxidation bond to difurazano[3,4-b,e]pyrazine anion gives a rise to the detonation performance of the title salts, while increasing their impact sensitivity meanwhile. Importantly, triaminoguanidinium 4,8-dihydrodifurazano[3,4-b,e]pyrazine (J4) has been successfully synthesized. The experimentally determined density and H50 value of J4 are 1.602 g/cm3 and higher than 112 cm, which are consistent with theoretical values, supporting the reliability of calculation methods. J4 proves to be a thermally stable and energetic explosive with decomposition peak temperature of 216.7 °C, detonation velocity 7732 m/s, and detonation pressure 25.42 GPa, respectively. These results confirm that the derivative work in furazanopyrazine compounds is an effective strategy to design and screen out potential candidates for high-performance energetic salts.

Comparative studies on structure, sensitivity and mechanical properties of CL-20/DNDAP cocrystal and composite by molecular dynamics simulation.

Molecular dynamics simulation was performed on 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), 2,4-dinitro-2,4-diazapentane (DNDAP), and CL-20/DNDAP cocrystal and composite under COMPASS force field at different temperatures. The binding energy (E bind), radial distribution function (RDF), trigger bond length, cohesive energy density (CED) and mechanical properties were studied and compared. The results show that the binding energy of the cocrystal is evidently higher than that of the composite at the same temperature. RDF analysis reveals that hydrogen bonds and vdW forces between CL-20 and DNDAP exist in both CL-20/DNDAP cocrystal and composite, and the interactions in the cocrystal are stronger than those in the composite. The maximum trigger bond length decreases in the order ε-CL-20 > CL-20/DNDAP composite > CL-20/DNDAP cocrystal. Moreover, the rigidity and stiffness of the cocrystal and composite decrease compared to that of CL-20, while the ductility and elasticity are better than that of the two pure components. These results demonstrate that CL-20/DNDAP cocrystal might be very promising in explosive applications.