Bis‐propargylhydroquinone (BPHQ) is an alkyne functionalized isocyanate‐free curing agent for hydroxyl terminated azido polymers. Conventionally, glycidyl azide polymer (GAP) is cured by isocyanate based curatives, which are toxic and hygroscopic in nature. The reaction between hydroxyl end group of GAP and isocyanate is highly sensitive to moisture causing voids in the propellant, leading to poor mechanical properties. Herein, an alternate approach was adapted to exploit 1,3‐dipolar cycloaddition reaction between azido group of GAP and the triple bond (–C≡CH) of BPHQ without catalyst at 50 °C forming triazole crosslinked polymer. The curing behavior of GAP‐BPHQ system was studied by rheological method and based on the results the gel time was determined. In addition, the reaction between GAP and BPHQ was carried out with various GAP/BPHQ ratios (0.9 to 2.5) and effects on mechanical properties of resulting triazole polymers were investigated. Post curing hardness of GAP‐BPHQ binder system was tested by surface Shore‐A hardness measurement. The compatibility of BPHQ with energetic oxidizers such as ammonium dinitramide (ADN) and hydrazinium nitroformate (HNF) were also studied by differential scanning calorimetery (DSC) technique and showed good compatibility. The activation energy (Ea) of cured GAP‐BPHQ binder was evaluated by DSC using Ozawa and Kissinger methods and are found to be 33.55 and 33.16 kcal mol–1, respectively. The advantage of this curing system between GAP and BPHQ is unaffected by moisture as compared to isocyanate based urethane systems and also no need to control humidity during the processing of propellant. The experimental results reveal that triazole crosslinked polymer system could be a better choice to develop novel energetic binder systems for explosives as well as propellants composition with improved performance and eco‐friendly nature.
This paper discusses the synthesis and characterisation of cobalt (Co), nickel (Ni) and copper (Cu) carbohydrazide nitrates. In differential scanning calorimetry (DSC), the complexes exhibited exothermic decomposition indicating their energetic nature. The commencement of decomposition was observed at 220 °C for Ni complex, and at 160 °C for Co complex whereas that of Cu complex occurred at 75 °C. In view of the better thermal stability, Ni and Co complexes were selected for further study. The activation energy of decomposition of Ni and Co complexes were found to be 47 kcal/mol and 60 kcal/mol respectively. Impact and friction sensitivity test results revealed relatively lower vulnerability of carbohydrazide cobalt nitrate. Its incorporation in an ammonium perchlorate (AP)-based composite propellant led to 9-19 per cent enhancement whereas that of carbohydrazide nickel nitrate resulted in 28-74 per cent enhancement in burning rates in the pressure range 1.9 MPa to 8.8 MPa. Exothermic decomposition of the coordination complexes on propellant surface and involvement of metal at molecular level formed on decomposition of the complexes in combustion environment of composite propellant may be attributed to the catalytic effect of this class of compounds on the lines of reported literature.
This study reports the synthesis and characterization of a novel class of non-isocyanate curing agents based on bis-propargyl aromatic esters 2a–e and ethers 4a–c.
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