Generation of Melamine Polymer Condensates upon Hypergolic Ignition of Dicyanamide Ionic Liquids

摘要

Fuels that can be ignited chemically under ambient conditions --upon contact with an oxidizing agent - are referred to as hypergols. Since 2008, a number of ionic liquids (ILs) have been reported to be hypergolic when reacted with common oxidizers, such as HNO_(3). In this study, using electrospray ionization mass spectrometry (ESI-MS), we discovered that the reaction between ILs comprising fuel-rich dicyanamide (DCA) anions and HNO_(3) yields a precipitate that is composed of cyclic triazines, including melamine and its polymers. The concurrent formation of precipitate siphons materials from the hypergolic reaction pathway, limiting the energy capacity of a fuel. The results of model experiments obtained under various experimental conditions suggest that the key components necessary for the formation of the major polymers are DCA anions and nitric acid. Polymerization occurs even at lower concentration of reagents, when neither hypergolic ignition nor notable heating of the reaction mixture take place. The reaction of DCA ILs with aqueous HNO_(3) therefore represents a new, facile, ambient method to synthesize cyclic azines, which can be tuned by choosing various different IL precursors.