Alkyl Vinyl Imidazolium Ionic Liquids as Fuel Binders for Photo-curable Energetic Propellants

Polymers, made of energetic ionic liquid building blocks, are used as the fuel-binder part in propellant compositions. These compositions exhibit desired mechanical and energetic properties and may serve as a photoactive feed for 3D printable propellants. Quaternary vinyl imidazolium energetic salts, having perchlorate and nitrate counter ions, are used as monomers in fuel-binder polymers, while ammonium perchlorate is used as the heterogeneous oxidizer in the composition. The vinyl groups on the heterocyclic cations provide covalent interconnecting sites for the construction of the polymer backbone and binding sites for in-chain plasticizers, enabling control over mechanical and initiation sensitivity properties in the cured composite product. The advantageous oxygen balance and heat of formation values of these ionic liquid monomers, along with their ability to photo-polymerize, allow both the effective dispersion and reduced ratios of the heterogeneous oxidizer content without compromising the energetic properties of the resultant propellant. An intermolecular interaction between the heterocyclic imidazolium units was identified, which enables noncovalent reinforcement and may explain some of the observed properties of the compositions. Pressure-independent burn rates were achieved in compositions containing 2-ethoxyethyl acrylate plasticizer, thus avoiding the need for additional additives, stratification, and geometrical constraints on the burning bulk.