Crystal Structure of Poly(p-Aminohippuric Acid) Produced by Thermal Polymerization.

Abstract

Synthesis of poly (p-aminohippuric acid) (PPAHA) was carried out using two different polymerization techniques: thin-film melt-polymerization and single-crystal thermal-polycondensation. Crystal structure and morphology of PPAHA were examined by means of the electron microscopy. Lamellar crystals were observed on the thin-film melt-polymerized specimen. The electron diffraction pattern from the lamellar crystal suggested the pseudohexagonal lattice structure. Comparing the result with the packing of chains in the unit cell of poly (p-phenylene terephthalamide) crystal, it was concluded that the unit cell of PPAHA was orthorhombic (a=0.48nm, b=0.84nm and c(chain axis)=1.9nm), the space group of which was reasonably assumed to be P212121, and that the diffraction pattern was superimposition of the reflections from the twins with three different orientations (± 60° and ± 120°).In the case of the thermally polymerized material from the p-aminohippuric acid single crystal, numerous fibrils (100-200nm in diameter and 50-200μm in length) appeared over the surface of the specimen after annealing longer than 1000h, in which the molecular chains were considered to be normal to the basal plane, since the diffraction pattern always corresponded to the projection of the a *-b* plane in the reciprocal lattice of PPAHA crystal.