Scale-up of energetic polyphosphazenes- development of a continuous nitration process.

Abstract

Energetic polyphosphazenes (PPZs) are a recently developed category of energetic polymers in which structural variation can be deliberately employed to vary, and thereby potentially to optimize, phys. and chem. properties for particular applications. These products offer higher energy densities and lower glass transition temps. than existing materials such as GAP, polyNIMMO and polyGLYN, but to date have been prepd. only on a lab. multi-gram scale. This paper now records key elements of the synthetic scale-up of one low hazard product [2,2,2-trifluoroethan-1-oxy/5,6-dinitratohexan-1-oxy polyphosphazene, (1)], leading to construction of a kilogram scale semi-tech nitration plant. Although focussed on the prepn. of a single baseline material (1) this work charts the way, through minor process variations, to a range of different nitrato substituted polyphosphazenes, possessing progressively variable phys. and energetic properties. A primary issue in scaling-up the prodn. of (1) has been its susceptibility to degrdn. by the reaction medium. This has been addressed through the construction of a small-scale flow nitrator to minimize contact time between product and spent acid and to improve temp. control. This technique has reduced batch to batch variation and facilitated larger-scale synthesis. Processing parameters investigated include: temp., residence time, PPZ:acid ratio and PPZ:solvent ratio. Optimization of these parameters has yielded the necessary conditions to produce high quality product where the extent of nitration achieved is 98+%, with a yield of ca 87%. These data have provided the basic information necessary to design and construct a kilo-scale tech. demonstrator plant. The complex phase behavior of reaction and extn. solns. during work up has been explored to facilitate product recovery and prevent its degrdn. Once commissioned the demonstration plant, which is now available, will provide larger quantities of product for evaluation, together with the necessary experience to transfer this material to com. prodn. [on SciFinder(R)]