STRUCTURAL-ANALYSIS OF HIGHLY ORIENTED POLY(P-PHENYLENE TEREPHTHALAMIDE) BY N-15 SOLID-STATE NUCLEAR-MAGNETIC-RESONANCE

The structure of an aromatic polyamide, poly(p-phenylene-terephthalami de) (PPTA), was studied in the solid state using N-15 nuclear magnetic resonance (NMR) spectroscopy. Spectra of uniaxially aligned molecules placed with the axis of alignment both parallel with and perpendicula r to the applied magnetic field were analyzed to yield the orientation s of specific molecular bonds with. respect to the fiber axis. The N-1 5 chemical shift tensor was characterized by simulating powder pattern spectra of both PPTA and a model compound, benzanilide. Chemical shif t and dipolar coupled chemical shift line shapes were calculated throu gh Euler angle transformations from the principal axis system (PAS) re ference frame to the fiber axis system (FAS) frame. The orientations o f NH and NC' bonds in PPTA are determined as well as the orientational distribution of the PPTA fiber axis. The structural parameters determ ined for PPTA are compared with those obtained by X-ray diffraction.