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.