Burn Rate Modification with Carborane Polymers
Technical Report,01 Jan 2011,31 Dec 2013
ARDEC, METC, RDAR-MEE-W Picatinny Arsenal United States
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In the past, propellants containing boron clusters like n-hexyl carborane demonstrated an improved burn rate, decreased pressure exponent, and maintained a high energy output. However, the technology was hampered by expensive and hazardous synthesis as well as migration issues of the n-hexyl carborane plasticizer. A new, affordable synthesis procedure of decaborate salts was established at the University of Missouri-Columbia, which provides material for alkylation and subsequent synthesis to carboranylmethyl acrylate. In this paper, the investigation of the integration of covalently-bonded boron achieved through copolymerization in various binder polymers is presented. Since pure carboranylmethyl acrylate polymer is a solid crystalline material at room temperature, it was co-polymerized to produce a material suitable for formulations. The co-polymerization investigated was a combination of carboranylmethyl acrylate, butyl acrylate, and 2-hydroxyethyl acrylate. The boron-rich carborane was intended to serve as the high energy fuel portion of the polymer, the butyl acrylate provided a glass transition temperature below room temperature and low viscosity, and the hydroxylethyl acrylate contributed a cross-linkable moiety. The resulting polymer was used in a cast-cure formulation containing aluminum and ammonium perchlorate in order to test the effect of the carborane additive on the formulation burn rate when compared to a hydroxyl-terminated polybutadiene baseline. Strand burn rate testing demonstrated a distinctive increase in the burn rate for the carborane containing formulation. Synthesis and characterization of the carborane-based polymer are discussed along with the designed formulation. Further test data including sensitivity and thermal characterization are presented.
- Ammunition and Explosives
- Inorganic Chemistry
- Organic Chemistry