Factors governing the three-dimensional hydrogen-bond network structure of poly(m-phenylene isophthalamide) and a series of its model compounds. 3. Energy terms indispensable to the crystal structure prediction

Abstract

To clarify the factors that govern the complicated three-dimensional hydrogen-bond network structure of poly(m-phenylene isophthalamide) and its model compounds, the packing energy calculations were performed with computer simulation software (Polymorph Predictor) and the important energy terms were extracted successfully. The crystal structures were predicted with and without the various types of interaction terms being taken into consideration and were compared with the X-ray-analyzed structures. Initially, the conformation analysis was made for a single molecule. However, the structure with the lowest energy did not always correspond to the actually observed structure. This finding suggested the importance of intermolecular, as well as intramolecular, interactions. By performing the lattice-energy calculations with and without various types of intermolecular interactions being taken into consideration, and by comparing the results with the observed structures, it has been found that the van der Waals interaction was a primarily important factor in the prediction of the molecular packing structures; however, the electrostatic (and hydrogen-bond) interaction could not be ignored at all. In other words, a good and sensitive balance between these interaction terms was quite important for obtaining a successful reproduction of the observed molecular packing structures of the model compounds.