Generation of Crystallographic Packing Candidates with Fixed Helical Symmetry and Axial Advance: Application to Pi-2 Polyimide

A normal coordinate approach was used to generate ciystallographic packing candidates of a multitorsional polyimide synthesized from 3,3′,4,4′-benzophenonetetracarboxylic acid (BTDA) and 2,2-dimethyl-l,3-(4-aminophenoxy)propane (DMDA) (PI-2). Candidates were obtained under conditions of fixed axial advance of 24.6 Å per monomer, and imposed 2/1 helical or 1/0 transiational symmetry, consistent with the observed WAXD meridional layer line spacing [1]. The ability of comb in atori ally generated torsional states to adopt the desired geometry was examined. Necessary corrections to die conformational parameter equations originally derived by Kusanagi, et al. [2|, have been made. The procedure described allowed crystallographic conformations satisfying explicit geometric and MM3 intramolecular energy criteria to be generated for a linear multitorsional polyimide prior to the application of crystallographic screening or refinement procedures.