Oxetane Monomers Based On the Powerful Explosive LLM-116: Improved Performance, Insensitivity, and Thermostability.

3-Bromomethyl-3-hydroxymethyloxetane represents an inexpensive and versatile precursor for the synthesis of 3,3-disubstituted oxetane derivatives. In the present work, its synthesis was improved and energetic oxetanes based on the explosive LLM-116 (4-amino-3,5-dinitro-1H-pyrazole) prepared. Reaching detonation velocities and pressures of up to 7335 ms-1 and 20.9 GPa in combination with a high thermostability and insensitivity, these surpass the prior art by far. Next to a symmetric LLM-116 derivative, three asymmetric compounds were prepared using azido-, nitrato- and tetrazolyl-moieties. All compounds were intensively characterized by vibrational-, mass- and multinuclear (1 H, 13 C, 14 N) NMR spectroscopy, differential scanning calorimetry and elemental analysis. The molecular structures were elucidated by single crystal X-ray diffraction. Hirshfeld analysis allowed to estimate their sensitivity next to a practical evaluation using BAM standard procedures. Their performance was calculated using the EXPLO5 V6.04 code and a small-scale shock reactivity test and initiation test demonstrated their insensitivity and performance.

A GAP Replacement, Part 2: Preparation of Poly(3-azidooxetane) via Azidation of Poly(3-tosyloxyoxetane) and Poly(3-mesyloxyoxetane).

Despite the variety of energetic polyoxetane binders, the oxirane-based glycidyl azide polymer (GAP) has largely succeeded in the market due to its advantageous properties. Nevertheless, it suffers from various drawbacks such as non-uniform chain termination, possible chlorine content (flame retardant), and toxic epichlorohydrin required for its synthesis. These problems can be bypassed using the structurally related poly(3-azidooxetane). Unfortunately, it is only accessible in moderate yield by polymerization of 3-azidooxetane. Herein, we describe its synthesis by polymer-analogous transformation using the new polymers poly(3-tosyloxyoxetane) and poly(3-mesyloxyoxetane) as precursors. This results in a significantly increased yield and improved safety as handling of the very sensitive 3-azidooxetane is avoided. The aforementioned prepolymers were prepared using boron trifluoride etherate as well as triisobutylaluminum as catalysts. The latter provides polymers of particularly high molecular weight, and the corresponding poly(3-azidooxetane) species was obtained and studied for the first time. In order to shed light on the applicability of poly(3-azidooxetane) as a GAP substitute, it was thoroughly studied with regard to thermal behavior, energetic performance (EXPLO5), plasticizer compatibility, and curing. Moreover, the aquatic toxicity of all involved monomers was analyzed and compared to epichlorohydrin. Here, poly(3-azidooxetane) turned out as a fully adequate, if not more environmentally benign, substitute.

A GAP Replacement: Improved Synthesis of 3-Azidooxetane and Its Homopolymer Based on Sulfonic Acid Esters of Oxetan-3-ol.

In the field of energetic binders, only hydroxy-terminated glycidyl azide polymer (GAP) has found widespread application and prevailed in the market. However, oxiranes such as glycidyl azide (GA) allow two ring-opening modes during polymerization and thus lead to polymers of different termination causing inhomogeneous curing results. An elegant solution is the polymerization of 3-azidooxetane as only terminating primary hydroxyl groups are formed. Beyond this, poly(3-azidooxetane) and GAP are equal in other aspects due to the similar repetition unit. Since literature methods for the preparation of 3-azidooxetane either employed toxic solvents, gave low yields or impurified product, or could not be reproduced, a new synthesis method was developed to afford pure material and satisfying yields. The syntheses of toluene- and methanesulfonic acid esters of oxetan-3-ol as precursors were also significantly improved in comparison to the literature and their molecular structures elucidated by single-crystal X-ray diffraction. The aforementioned compounds and poly(3-azidooxetane) were intensively studied by vibrational and multinuclear NMR spectroscopy (1H, 13C, 14N), differential scanning calorimetry, and elemental analysis. The key compound, 3-azidooxetane, was compared to glycidyl azide regarding performance using the EXPLO5 V6.04 thermochemical code and their sensitivity toward external stimuli like shock and friction assessed according to BAM standard procedures.

3,3-Dinitratooxetane - an important leap towards energetic oxygen-rich monomers and polymers.

3-Substituted oxetanes are valuable monomers for modern ring-opening polymerizations. A new solid-state oxidizer, 3,3-dinitratooxetane (C3H4N2O7), which has an oxygen content of 62.2% was synthesized by the addition of N2O5 to oxetan-3-one. Monoclinic single crystals suitable for X-ray diffraction (ρ 1.80 g cm-3) were obtained by recrystallization from dichloromethane. In addition, 3-nitratooxetane was prepared by an improved method and 3-nitrato-3-methyloxetane was synthesized for the first time. Theoretical calculations were computed by the EXPLO5 software and additionally sensitivities towards impact and friction were determined.