Syntheses and X‐Ray Structures for Model Compounds of a Pyrimidinediyl‐Based Rigid‐Rod Aromatic Polyamide

A variety of model compounds for the pyrimidinediyl‐based rigid‐rod polyamide poly[imino‐(pyrimidine‐2,5‐diyl)‐imino‐tetraphthaloyl] (PPYMT) was prepared, in order to compare their conformations to several model compounds of the related, fully aromatic polymer poly( p ‐phenyleneterephthalamide) (PPTA). In particular, the structures of N ‐(2‐pyrimidyl)benzamide (PYMB) and its complexed form bis[( N ‐pyrimidin‐2‐yl)benzamide]nickel(II) dichloride (NiPYMB) were determined by X‐ray diffraction. The molecular packing in these crystals provides us with a model for the possible ‘cross‐linking’ of PPYMT fibers. The structures of the trimer model compounds N , N ′ ‐bis(2‐pyrimidyl)terephthalamide (PYTA) and N , N ′ ‐bis(benzoyl)‐2,5‐diaminopyrimidine (BDAP) yield information about the conformation of PPYMT chains and are compared to analogous model compounds of PPTA.