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Description Catalog Number Availability Unit Your Price Price Per QtyEven though a considerable number of various promising energetic polymers structurally containing tetrazole moieties have been devised to date [ 10 ], no studies have been performed so far on the synthesis of energetic polymers based on the glycidyl azide polymer, functionalized partially or completely by a commercially available, high-nitrogen 5-aminotetrazole heterocycle, and of their nitrated derivatives. Thus, with the aim of combining a set of useful properties typical of 5-AT and the energetic merits of GAP, the present study synthesized and evaluated key characteristics of new glycidyl polymers that carry 5-aminotetrazole (p-GAT) units and consolidate explosophoric moieties, such as aminotetrazole heterocycles and Ngroups (p-(GAT--GA)), within the single macromolecule. Moreover, a p-GAT-N polymer structurally containing additional oxidizing elements such as ONOgroups and nitrate anions was synthesized herein by nitration of the p-GAT tetrazole homopolymer. Using p-(GAT--GA) plasticized azide copolymers, we examined rheokinetic and viscosity relationships and demonstrated the feasibility of preparing energy-rich polymeric binders cross-linked with 1,2,3-triazole heterocycles. The structures of all the resultant compounds were characterized by a set of spectroscopic methods (H,C NMR and IR spectroscopies) and elemental and GPC analyses. The basic characteristics of the synthesized polymers (density, nitrogen content, decomposition temperature) were measured.
In particular, 5-Aminotetrazole (5-AT) is among the most high-nitrogen, commercially available, starting tetrazole synthons for the synthesis of a broad array of energetic materials [ 42 46 ]. The 5-AT molecule is made up of linearly conjugated, heterocyclic N&#;N, N=N, C&#;N and C=N bonds and an exocyclic NHgroup and contains 82.3% nitrogen. Having quite a high energetic potential, 5-aminotetrazole is not sensitive to mechanical stimuli [ 42 ]. Moreover, a rather reactive exocyclic amino group being present in the tetrazole heterocycle offers opportunities for chemical modification of the group and for insertion of additional explosophoric groups (for example, =N&#;NO, &#;NH&#;NO, NOanion) into the energy-rich molecule of tetrazole, which provides great opportunities for the molecular construction of novel energy-rich compounds based thereon [ 47 52 ].
In recent time, tetrazole heterocycles, among the series of explosophoric functional groups, have aroused considerable interest in the chemistry of high-energy materials, as well as in the development of energetic polymers [ 28 39 ]. Tetrazoles are a unique class of high-nitrogen, aromatic molecular cages that combine a high positive heat of formation and density and good thermal stability, together with a low toxicity and susceptibility to mechanical stimuli [ 40 41 ].
That said, despite having positive characteristics, GAP is not free of drawbacks that hinder or restrict its practical use in energy-rich materials [ 16 18 ]. To overcome the existing drawbacks, different authors are conducting research on modifying the structural arrangement of the azido polymer in order to create novel GAP-based energetic polymers with improved energetic and performance characteristics [ 19 27 ].
From among the energetic polymers, glycidyl azide polymer (GAP) is one of the most common and widely studied [ 3 4 ]. The structure of GAP represents a linear polyester macromolecule whose side chain carries explosophoric azidomethyl groups. Because of the acceptable density level [ 5 ], good thermal stability [ 6 7 ], positive enthalpy of formation [ 8 ] and good compatibility with constituents of energetic materials [ 9 12 ], the said azido polymer is one of the most promising alternatives to inert polymeric binders (such as HTPB) to achieve a higher energetic performance of systems based thereon [ 13 15 ].
The starting chlorine polymer p-ECH-BD and GAP were prepared by the reported procedures [ 23 ], and sodium 5-aminotetrazolate, 1,2,3-tris(prop-2-ynyloxy)propane (TPEG) and N-(2-hydroxyethyl)tetrazole (HET) were prepared by the procedures reported in [ 53 55 ], respectively. All the other chemicals used were purchased from commercial suppliers and employed as received. The IR spectra of the synthesized polymers were recorded on a Simex FT-801 IR-Fourier spectrometer.H andC NMR spectra were taken on a Bruker AV-400 (Bruker Corporation, USA) at 400 MHz and 100 MHz, respectively, by using DMSO-d6 signals (δ 2.5 ppm forH and 39.5 ppm forC) as internal standard. Elemental analysis of the polymers was performed on a FlashEA CHNS analyzer (Thermo Fisher Scientific Inc., Milan, Italy). The residual chlorine content was quantified on a Multi EA Cl analyzer (Analytik Jena AG, Jena, Germany). The molecular weight of the polymers was measured by gel-permeation chromatography (GPC) on an LC-20 Prominence high-performance liquid chromatograph (Shimadzu, Japan) with a series of three 300 × 7.5 mm ResiPore columns and a refractive index detector, 3 µm filler particle size (multiparous type) and 7.5 × 50 mm ResiPore Guard pre-columns (Agilent Technologies, Santa Clara, CA, USA). For calibration, polyethylene glycol (PEG) standards with a narrow molecular-weight distribution (M/M= 1.00&#;1.09; Agilent Technologies, Santa Clara, CA, USA) were utilized. Eluent was: DMF for GPC (PanReac AppliChem, Darmstadt, Germany) with added LiBr (0.1% concentration). Chromatographic conditions were: 25 °C thermostat temperature, 1.0 mL/min volumetric elution flowrate, 100 μL sample injection volume, 30 g/L and sample concentration. The densities of the synthesized samples were experimentally measured on an AccuPyc II V1.05 helium pycnometer (Micromeritics, USA). Thermal stability was measured on a DSC 822e (Mettler Toledo, Zurich, Switzerland) instrument at a linear heating rate of 10 °C/min in the range of 20&#;400 °C under nitrogen. The viscosity measurements were performed on a Brookfield LV DV-II viscometer with a cone&#;plate system and a Brookfield CP-52 spindle (Brookfield, WI, USA). The temperature during the experiments was controlled by a TC-150AP circulating bath (Brookfield, WI, USA).
CAUTION! All the azido- and tetrazole-containing compounds and the nitrated derivatives thereof are potentially explosion-hazardous energetic materials, though no hazards were observed while synthesizing and handling these compounds. Nonetheless, additional careful measures of precaution are required when dealing with these compounds (grounded equipment, Kevlar® gloves, Kevlar® sleeves, face shield, leather lab coat, ear plugs and protective shield during the reaction).
Preparation of Glycidyl 5-Aminotetrazole Polymer (p-GAT). Into a three-neck flask (100 mL) equipped with a magnetic stirrer, a thermometer and a reflux condenser with a calcium chloride drying tube was poured DMF (40 mL), and p-ECH-BD (9.25 g, 100 mmol) was added with stirring. The whole was heated to 130 °C, afterwards sodium 5-aminotetrazolate (16.07 g, 150 mmol) was added. The resultant reaction mixture was stirred at 130 °C until the Beilstein test showed no chlorine. Upon reaction completion, the mixture was cooled to room temperature, and the precipitate as salts was collected by filtration. The polymeric solution was poured into isopropanol with vigorous stirring, and the precipitated product was separated by filtration. The resultant polymer was additionally purified by re-precipitation from a water&#;acetone mixture (water/acetone = 30/70 wt.%) into isopropanol. The polymer concentration in the water&#;acetone mixture was 25 wt.%. Following several washings with isopropanol and drying until constant weight at 80 °C in vacuo, the p-GAT homopolymer (7.32 g, 51.9%) was obtained as a white powder. IR spectrum (KBr), ν, cm&#;1 was: &#; (NH2), &#; (CH, CH2 of the polymeric chain), &#; (C=N), &#;, &#;757 (NCN, NN, CN of the tetrazole ring), (C&#;O&#;C of the polymeric chain). 1H NMR (400 MHz, DMSO-d6), δ, ppm was: 6.62 (s, 2H, NH2 N1-isomer of 5-AT), 5.99 (s, 2H, NH2 N2-isomer of 5-AT), 4.51&#;3.30 (proton signal region: &#;CH&#;O, &#;CH2&#;O groups of the chain and &#;CH2 related to the 5-AT heterocycle), 1.52 (s, 2H, &#;CH2 of BDO). 13C NMR (100 MHz, DMSO-d6), δ, ppm was: 167.45 (C&#;NH2 N2-isomer of 5-AT), 156.52 (C&#;NH2 N1-isomer of 5-AT), 78.15&#;77.17 (&#;O&#;CH), 71.86&#;68.12 (&#;O&#;CH2), 53.29 (&#;CH2&#;N of 5-AT), 26.25&#;25.90 (&#;CH2 of BDO). Elemental analysis was: calcd (%) for C4.2H7.5N5.1 (146.49): C 34.76; H 5.15; N 48.29; found (%): C 35.01; H 5.18; N 47.95.
Nitration of Glycidyl 5-Aminotetrazole Polymer (p-GAT-N). The p-GAT-N polymer was prepared by dissolving the p-GAT homopolymer (3.67 g, 26 mmol) in excess concentrated HNO3 (65% conc., 26 mL) with stirring at room temperature. The solution was heated to 96&#;100 °C and stirred for 10 min. The cooled reaction mass was poured into a great amount of ice and washed with distilled water, until neutral wash waters was achieved, and with isopropanol. The filtered product was dried at 50 °C in vacuo until constant weight to furnish a light-yellow powder (1.58 g, 29.7%). IR spectrum (KBr), ν, cm&#;1 was: &#; (NH2), &#; (CH, CH2 of the polymeric chain), , , (ONO2), (C=N), , , (NO3&#;), &#;710 (NCN, NN, CN of the tetrazole ring), (C&#;O&#;C of the polymeric chain) 1H NMR (400 MHz, DMSO-d6), δ, ppm was: 8.90 (s, 6H, NH+NH2 N1-isomer, NH+NH2 N2-isomer), 4.80&#;3.40 (proton signal region: &#;CH&#;O, &#;CH2&#;O groups of the chain and &#;CH2 related to the 5-AT heterocycle), 1.51 (s, 2H, &#;CH2 of BDO). 13C NMR (100 MHz, DMSO-d6), δ, ppm was: 153.62 (C&#;NH2 N2-isomer of 5-AT), 152.50 (C&#;NH2 N1-isomer of 5-AT), 79.31&#;76.15 (&#;O&#;CH), 71.60&#;66.63 (&#;O&#;CH2), 53.56 (&#;CH2&#;N of 5-AT), 25.89 (&#;CH2 of BDO). Elemental analysis was: calcd (%) for C4.2H8.4N6.0 (208.83): C 24.16; H 4.05; N 40.38; found (%): C 25.33; H 4.88; N 40.10.
Preparation of Glycidyl 5-Aminotetrazole and Glycidyl Azide Copolymers (p-(GAT-co-GA)). Into a three-neck flask (100 mL) fitted with a magnetic stirrer, a thermometer and a reflux condenser with a calcium chloride drying tube was poured DMF (40 mL), and p-ECH-BD (9.25 g, 100 mmol) was added with stirring. The whole was heated to 130 °C; afterwards, sodium 5-aminotetrazolate (14.46 g, 135 mmol), NH4Cl (0.80 g, 15 mmol) and NaN3 (0.98 g, 15 mmol) were added successively. The stirring was continued at 130 °C until the Beilstein test showed no chlorine. Upon reaction completion, the reaction mass was cooled down, and the precipitate was collected by filtration. The polymeric solution was poured into isopropanol with vigorous stirring, and the precipitated product was separated by filtration. The resultant polymer was additionally purified by re-precipitation from a water&#;acetone mixture (water/acetone = 30/70 wt.%) into isopropanol. The polymer concentration in the water&#;acetone mixture was 25 wt.%. Several washings with isopropanol and drying at 50&#;55 °C in vacuo until constant weight afforded the p-(GAT-
co
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-GA)-14 copolymer as a cream-colored powder (7.57 g, 56.9%). IR spectrum (KBr), ν, cm&#;1 was: &#; (NH2), &#; (CH, CH2 of the polymeric chain), (N3), &#; (C=N), &#;, &#;759 (NCN, NN, CN of the tetrazole ring), (C&#;O&#;C of the polymeric chain). 1H NMR (400 MHz, DMSO-d6), δ, ppm was: 6.62 (s, 2H, NH2 N1-isomer of 5-AT), 5.99 (s, 2H, NH2 N2-isomer of 5-AT), 4.52&#;3.30 (proton signal region: &#;CH&#;O, &#;CH2&#;O groups of the chain and &#;CH2 associated with N3 and the 5-AT heterocycle), 1.52 (s, 2H, &#;CH2 of BDO). 13C NMR (100 MHz, DMSO-d6), δ, ppm was: 167.46 (C&#;NH2 N2-isomer of 5-AT), 156.52 (C&#;NH2 N1-isomer of 5-AT), 78.19&#;77.19 (&#;O&#;CH), 71.00&#;69.14 (&#;O&#;CH2), 53.30 (&#;CH2&#;N of 5-AT), 51.37 (&#;CH2&#;N3) 26.26&#;25.90 (&#;CH2 of BDO). Elemental analysis was: calcd (%) for C4.1H7.1N4.7 (139.19): C 35.03; H 5.17; N 47.50; found (%): C 35.42; H 5.23; N 46.98.The p-(GAT-
co
-GA)-22 copolymer was synthesized and purified under the same conditions as for p-(GAT-co
-GA)-14, except the fact that to the solution of p-ECH-BD (9.25 g, 100 mmol) in DMF (40 mL) were added sodium 5-aminotetrazolate (13.39 g, 125 mmol), NH4Cl (1.34 g, 25 mmol) and NaN3 (1.63 g, 25 mmol). The result was the p-(GAT-co
-GA)-22 copolymer as a cream-colored powder (8.00 g, 61.7%). IR spectrum (KBr), ν, cm&#;1 was: &#; (NH2), &#; (CH, CH2 of the polymeric chain), (N3), &#; (C=N), &#;, &#;758 (NCN, NN, CN of the tetrazole ring), (C&#;O&#;C of the polymeric chain). 1H NMR (400 MHz, DMSO-d6), δ, ppm was: 6.64 (s, 2H, NH2 N1-isomer of 5-AT), 6.00 (s, 2H, NH2 N2-isomer of 5-AT), 4.51&#;3.12 (proton signal region: &#;CH&#;O, &#;CH2&#;O groups of the chain and &#;CH2 associated with N3 and the 5-AT heterocycle), 1.52 (s, 2H, &#;CH2 of BDO). 13C NMR (100 MHz, DMSO-d6), δ, ppm was: 167.48 (C&#;NH2 N2-isomer of 5-AT), 156.52 (C&#;NH2 N1-isomer of 5-AT), 78.28&#;77.20 (&#;O&#;CH), 71.86&#;69.12 (&#;O&#;CH2), 53.30 (&#;CH2&#;N of 5-AT), 51.38 (&#;CH2&#;N3) 26.26&#;25.90 (&#;CH2 of BDO). Elemental analysis was: calcd (%) for C4.0H7.0N4.6 (136.40): C 35.22; H 5.18; N 46.93; found (%): C 35.76; H 5.26; N 46.23.The p-(GAT-
co
-GA)-56 copolymer was synthesized under the same temperature&#;time conditions as for p-(GAT-co
-GA)-14, except for the fact that to the solution of p-ECH-BD (9.25 g, 100 mmol) in DMF (40 mL) were added sodium 5-aminotetrazolate (9.63 g, 90 mmol), NH4Cl (3.21 g, 60 mmol) and NaN3 (3.90 g, 60 mmol). Upon reaction completion, the reaction mass was cooled down, the precipitate was collected by filtration and DMF was evaporated at 85&#;90 °C in vacuo. The residue was mixed with acetone in a ratio of 50/50 wt.%, and the resulting suspension was passed through a Captiva premium syringe filter having a polytetrafluoroethylene membrane and a pore size of 0.45 µm (Agilent Technologies, USA). The polymeric solution was poured into water with vigorous stirring. Several washings with water and drying at 90 °C in vacuo until constant weight furnished the p-(GAT-co
-GA)-56 copolymer as a high-viscosity mass (8.25 g, 71.0%). IR spectrum (film), ν, cm&#;1 was: &#; (NH2), &#; (CH, CH2 of the polymeric chain), (N3), &#; (C=N), &#;, &#;757 (NCN, NN, CN of the tetrazole ring), (C&#;O&#;C of the polymeric chain). 1H NMR (400 MHz, DMSO-d6), δ, ppm was: 6.61 (s, 2H, NH2 N1-isomer of 5-AT), 6.00 (s, 2H, NH2 N2-isomer of 5-AT), 4.52&#;3.14 (proton signal region: &#;CH&#;O, &#;CH2&#;O groups of the chain and &#;CH2 associated with N3 and the 5-AT heterocycle), 1.53 (s, 2H, &#;CH2 of BDO). 13C NMR (100 MHz, DMSO-d6), δ, ppm was: 167.50 (C&#;NH2 N2-isomer 5-AT), 156.51 (C&#;NH2 N1-isomer of 5-AT), 78.49&#;77.32 (&#;O&#;CH), 71.89&#;69.13 (&#;O&#;CH2), 53.30 (&#;CH2&#;N of 5-AT), 51.48 (&#;CH2&#;N3) 26.29&#;25.90 (&#;CH2 of BDO). Elemental analysis was: calcd (%) for C3.7H6.4N3.9 (122.52): C 35.98; H 5.22; N 44.70; found (%): C 36.71; H 5.33; N 43.81.The p-(GAT-
co
-GA)-75 copolymer was synthesized under the same temperature&#;time conditions as for p-(GAT-co
-GA)-14, except for the fact that to the solution of p-ECH-BD (9.25 g, 100 mmol) in DMF (40 mL) were added sodium 5-aminotetrazolate (8.03 g, 75 mmol), NH4Cl (4.01 g, 75 mmol) and NaN3 (4.88 g, 75 mmol). Upon reaction completion, the mass was cooled down, the precipitate was collected by filtration and the solvent was evaporated at 85&#;90 °C in vacuo. The residue was mixed with dichloromethane (50 mL), and the resulting suspension was passed through a Captiva premium syringe filter having a polytetrafluoroethylene membrane and a pore size of 0.45 µm (Agilent Technologies, Santa Clara, CA, USA). The polymeric solution was washed thrice with water. After it was dried over MgSO4, and the solvent was evaporated at 80&#;90 °C in vacuo until constant weight, the p-(GAT-co
-GA)-75 copolymer was obtained as a viscous mass (6.65 g, 61.2%). IR spectrum (film), ν, cm&#;1 was: &#; (NH2), &#; (CH, CH2 of the polymeric chain), (N3), &#; (C=N), &#;, &#;748 (NCN, NN, CN of the tetrazole ring), (C&#;O&#;C of the polymeric chain). 1H NMR (400 MHz, DMSO-d6), δ, ppm was: 6.62 (s, 2H, NH2 N1-isomer of 5-AT), 6.01 (s, 2H, NH2 N2-isomer of 5-AT), 4.53&#;3.14 (proton signal region: &#;CH&#;O, &#;CH2&#;O groups of the chain and &#;CH2 associated with N3 and the 5-AT heterocycle), 1.54 (s, 2H, &#;CH2 of BDO). 13C NMR (100 MHz, DMSO-d6), δ, ppm was: 167.51 (C&#;NH2 N2-isomer of 5-AT), 156.50 (C&#;NH2 N1-isomer of 5-AT), 78.50&#;77.34 (&#;O&#;CH), 71.90&#;69.14 (&#;O&#;CH2), 53.35 (&#;CH2&#;N of 5-AT), 51.50 (&#;CH2&#;N3) 26.72&#;26.22 (&#;CH2 of BDO). Elemental analysis was: calcd (%) for C3.3H5.6N3.3 (107.60): C 36.49; H 5.26; N 43.17; found (%): C 37.27; H 5.37; N 42.26.Want more information on 5-Aminotetrazole Monohydrate? Feel free to contact us.