Recrystallization of CL-20 and HNFX from Solution for Rigorous Control of the Polymorph Type: Part I, Mathematical Modeling using Molecular Dynamics Method

Abstract

The recrystallization of CL-20 and HNFX to form different polymorphs was investigated by employing combinations of computations (polymorph predictions with and without the presence of the solvent molecules in the molecular dynamics based calculations) and experimental analyses, including micro-crystallization under a myriad of conditions, novel means of crystallization, analysis of polymorphs using X-ray powder diffraction, and Rietveld analysis, and the use of conventional methods including DSC, TGA, polarized microscopy and SEM (with the experimental results reported in Part II of this paper). In the investigation all three groups of solvents: polar protic, non-polar aprotic, and dipolar aprotic solvents were employed. Our computations have revealed (in agreement with earlier studies) that polymorphs with various densities for both CL-20 and HNFX are possible. However, as part II of this paper will show although the experiments revealed different polymorph types, α, β, γ, ϵ for CL-20 under different recrystallization conditions all of our experimental work for HNFX have resulted in crystals pertaining to Ci R-3, which is the only known polymorph of HNFX.