DETAILED ATOMISTIC SIMULATION OF ORIENTED PSEUDOCRYSTALLINE POLYMERS AND APPLICATION TO A STIFF-CHAIN ARAMID

Atomistic modeling methods are applied to the study of microstructure formation in the solid state of a highly ordered polymer. The calculations are adapted to the consideration of local structural imperfections, with retention of the long-range crystalline contribution to structure compaction and cohesive energy. The simulation technique employs no adjustable parameters and incorporates the simultaneous minimization of total potential energy with respect to both intramolecular and intermolecular degrees of freedom. The method is applied to the analysis of the solid state of the rigid-rod polymer poly(p-phenyl-eneterephthalamide). The simulation results, based solely on a potential energy criterion, suggest that such rodlike polymers may realize local helix distortions and multiple packing geometries of chains as a consequence of the substantial magnitude of intermolecular forces in effect, in conjunction with a disparity in the specificity of interactions in the different spatial directions. However, all predicted structures posses the common features of chain extension and hydrogen-bonded sheet formation, with polymorphism hinging primarily on the nature of packing between sheets.